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{{short description|Concept of collecting solar power in outer space and distributing it to Earth}}{{Distinguish|Solar panels on spacecraft}}{{Speculation|date=May 2016}}
{{essay|date=May 2011}}
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{{Sustainable energy}}
{{Renewable energy sources}}


], for fixed flat-plate collectors) due to the Earth's rotation.</div>]] '''Space-based solar power''' ('''SBSP''' or '''SSP''') is the concept of collecting ] in ] with solar power satellites (SPS) and distributing it to ]. Its advantages include a higher collection of energy due to the lack of ] and absorption by the ], the possibility of very little night, and a better ability to orient to face the Sun. Space-based solar power systems convert ] to some other form of energy (such as ]s) which can be transmitted through the atmosphere to receivers on the Earth's surface.


] have been in use since 1958, when ] used them to power one of its radio transmitters; however, the term (and acronyms) above are generally used in the context of large-scale transmission of energy for use on Earth.
'''Space-based solar power''' ('''SBSP''') is the concept of collecting ] in ] for use on ]. It has been in research since the early 1970s.


Various SBSP proposals have been researched since the early 1970s,<ref name="ESA-SBSP">{{cite web |date=15 April 2013 |url=http://www.esa.int/gsp/ACT/projects/sps.html |title=Space-based solar power |work=]–Advanced Concepts Team |access-date=August 23, 2015}}</ref><ref name="DOE-SBSP">{{cite web |date=6 March 2014 |url=https://www.energy.gov/articles/space-based-solar-power |title=Space-Based Solar Power |work=] (DOE)}}</ref> but {{asof|2014|lc=y}} none is economically viable with the space launch costs. Some technologists propose lowering launch costs with ] or with radical new space launch technologies ].
SBSP would differ from current solar collection methods in that the means used to collect energy would reside on an ]ing ] instead of on Earth's surface. Some projected benefits of such a system are:
* Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of ]. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth's surface.
* Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar ], generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most.<ref name="ReferenceB">Collection at Earth's ] can take place for 24 hours per day, but not consistently, and only for 6 months of the year.</ref>
* Elimination of ] concerns, since the collecting satellite would reside well outside of any atmospheric gasses, ] cover, wind, and other weather events.
* Elimination of ] and ] interference.
* Redirectable power transmission: A collecting satellite could possibly direct power on demand to different surface locations based on geographical ] or ] power needs.


SBSP also introduces several new hurdles, primarily the problem of transmitting energy from orbit to Earth's surface for use. Since ] are neither practical nor feasible with current technology, SBSP designs generally include the use of some manner of ]. The collecting satellite would convert solar energy into electrical energy on-board, powering a ] transmitter or ] emitter, and focus its beam toward a collector (]) on the Earth's surface. ] and ] damage could also become concerns for SBSP. Besides cost, SBSP also introduces several technological hurdles, including the problem of transmitting energy from orbit. Since wires extending from ] to an orbiting satellite are not feasible with current technology, SBSP designs generally include the ] with its associated conversion inefficiencies, as well as land use concerns for antenna stations to receive the energy at Earth's surface. The collecting satellite would convert solar energy into electrical energy, power a ] transmitter or ] emitter, and transmit this energy to a collector (or microwave ]) on Earth's surface. Contrary to appearances in fiction, most designs propose beam energy densities that are not harmful if human beings were to be inadvertently exposed, such as if a transmitting satellite's beam were to wander off-course. But the necessarily vast size of the receiving antennas would still require large blocks of land near the end users. The service life of space-based collectors in the face of long-term exposure to the space environment, including degradation from ] and ] damage, could also become a concern for SBSP.

As of 2020, SBSP is being actively pursued by Japan, China,<ref>{{cite web|url=https://www.cnbc.com/2019/03/15/china-plans-a-solar-power-play-in-space-that-nasa-abandoned-long-ago.html |title=China plans a solar power play in space that NASA abandoned decades ago |author1=Eric Rosenbaum |author2=Donovan Russo |date=March 17, 2019 |website=CNBC.com |access-date=19 March 2019 }}</ref> Russia, India, the United Kingdom,<ref>{{cite press release |url=https://www.gov.uk/government/news/uk-government-commissions-space-solar-power-stations-research|title=UK government commissions space solar power stations research |publisher=UK Space Agency |date=14 November 2020 |website=gov.uk|access-date=30 November 2020}}</ref> and the US.

In 2008, Japan passed its Basic Space Law which established space solar power as a national goal.<ref>{{Cite web|url=http://www.kantei.go.jp/jp/singi/utyuu/basic_plan.pdf|title=Basic Plan for Space Policy|date=June 2, 2009|access-date=May 21, 2016}}</ref> ] has a roadmap to commercial SBSP.

In 2015, the ] (CAST) showcased its roadmap at the International Space Development Conference. In February 2019, '']'' (科技日报, Keji Ribao), the official newspaper of the ], reported that construction of a testing base had started in Chongqing's Bishan District. CAST vice-president Li Ming was quoted as saying China expects to be the first nation to build a working space solar power station with practical value. Chinese scientists were reported as planning to launch several small- and medium-sized space power stations between 2021 and 2025.<ref>{{Cite web|title=我国有望率先建成空间太阳能电站-科技新闻-中国科技网首页 |url=http://www.stdaily.com/index/kejixinwen/2019-02/14/content_750019.shtml|access-date=2021-08-18|website=www.stdaily.com}}</ref><ref>{{Cite web|last=Needham|first=Kirsty|date=2019-02-15|title=Plans for first Chinese solar power station in space revealed |url=https://www.smh.com.au/world/asia/plans-for-first-chinese-solar-power-station-in-space-revealed-20190214-p50xtg.html|access-date=2021-08-18|website=The Sydney Morning Herald|language=en}}</ref> In December 2019, ] reported that China plans to launch a 200-tonne SBSP station capable of generating megawatts (MW) of electricity to Earth by 2035.<ref>{{Cite web |title=China to build space-based solar power station by 2035 - Xinhua {{!}} English.news.cn |url=http://www.xinhuanet.com/english/2019-12/02/c_138599015.htm|archive-url=https://web.archive.org/web/20191202081144/http://www.xinhuanet.com/english/2019-12/02/c_138599015.htm|url-status=dead|archive-date=December 2, 2019|access-date=2021-08-18|website=www.xinhuanet.com}}</ref>

In May 2020, the ] conducted its first test of solar power generation in a satellite.<ref>{{Cite web|url=https://www.forbes.com/sites/scottsnowden/2020/05/27/solar-power-experiment-launches-on-secret-space-plane/|date=May 27, 2020|title=Solar Power Experiment Launched by Navy Research Lab on X-37B Space Plane|website=]}}</ref> In August 2021, the ] (Caltech) announced that it planned to launch a SBSP test array by 2023, and at the same time revealed that ] and his wife Brigitte, both Caltech trustees, had been since 2013 funding the institute's Space-based Solar Power Project, donating over $100 million.<ref>{{Cite web|title=Caltech Announces Breakthrough $100 Million Gift to Fund Space-based Solar Power Project|url=https://www.caltech.edu/about/news/caltech-announces-breakthrough-100-million-gift-to-fund-space-based-solar-power-project|access-date=2021-08-18|website=California Institute of Technology|date=3 August 2021|language=en}}</ref><ref name=caltech2023edu>{{Cite web|title=In a First, Caltech's Space Solar Power Demonstrator Wirelessly Transmits Power in Space|url=https://www.caltech.edu/about/news/in-a-first-caltechs-space-solar-power-demonstrator-wirelessly-transmits-power-in-space|access-date=2023-06-01|website=California Institute of Technology|date=1 June 2023|language=en}}</ref> A Caltech team successfully demonstrated beaming power to earth in 2023.<ref name=caltech2023edu/>


]
]
== History == == History ==
]
The SBSP concept, originally known as Satellite Solar Power System (SSPS), was first described in November 1968.<ref>{{cite journal|first=Peter E.| last=Glaser| title=Power from the Sun: Its Future | journal=Science Magazine |date=22 November 1968 |volume=162 |issue=3856 |pages=857–861 |format=PDF |url=http://www.sciencemag.org/cgi/reprint/162/3856/857.pdf}}</ref> In 1973 ] was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g., from an SPS to Earth's surface) using ]s from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a ], on the ground.<ref name="Glaser"/>


In 1941, science fiction writer ] published<!--where?--> the science fiction short story "]", in which a space station transmits energy collected from the Sun to various planets using microwave beams. The SBSP concept, originally known as satellite solar-power system (SSPS), was first described in November 1968.<ref>{{cite journal |doi=10.1126/science.162.3856.857 |pmid=17769070 |title=Power from the Sun: Its Future |journal=Science |volume=162 |issue=3856 |pages=857–61 |year=1968 |last1=Glaser |first1=P. E. |bibcode=1968Sci...162..857G }}</ref> In 1973 ] was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g. from an SPS to Earth's surface) using ]s from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a ], on the ground.<ref name="Glaser" />
Glaser then was a vice president at ], Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems—chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research.<ref name="FS">], Maynard, O. E., Mackovciak, J., and Ralph, E. L, Arthur D. Little, Inc., "Feasibility study of a satellite solar power station", NASA CR-2357, NTIS N74-17784, February 1974</ref>


Glaser then was a vice president at ], Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems&nbsp;– chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space&nbsp;– it showed enough promise to merit further investigation and research.<ref name="FS">], Maynard, O. E., Mockovciak, J., and Ralph, E. L, Arthur D. Little, Inc., "Feasibility study of a satellite solar power station", NASA CR-2357, NTIS N74-17784, February 1974</ref>
Between 1978 and 1981, the ] authorized the ] and ] to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program.<ref></ref><ref></ref> The study remains the most extensive performed to date (budget 50 millions $).<ref name="Mankins"> U.S. House Subcommittee on Space and Aeronautics Committee on Science, Sep 7, 2000</ref> Several reports were published investigating the engineering feasibility of such an engineering project. They include:

* Resource Requirements (Critical Materials, Energy, and Land)<ref></ref>
=== Concept development and evaluation ===
]
]
* Financial/Management Scenarios<ref></ref><ref></ref>

* Public Acceptance<ref></ref>
Between 1978 and 1986, the ] authorized the ] (DoE) and ] to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program.<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-ProgramPlanJuly1977-August1980.pdf|title=Satellite Power System Concept Development and Evaluation Program July 1977 - August 1980. DOE/ET-0034, February 1978. 62 pages|access-date=2009-02-20|archive-date=2017-03-13|archive-url=https://web.archive.org/web/20170313135341/http://www.nss.org/settlement/ssp/library/1978DOESPS-ProgramPlanJuly1977-August1980.pdf|url-status=dead}}</ref><ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-ReferenceSystemReport.pdf|title=Satellite Power System Concept Development and Evaluation Program Reference System Report. DOE/ER-0023, October 1978. 322|access-date=2009-02-20|archive-date=2017-03-13|archive-url=https://web.archive.org/web/20170313135400/http://www.nss.org/settlement/ssp/library/1978DOESPS-ReferenceSystemReport.pdf|url-status=dead}}</ref> The study remains the most extensive performed to date (budget $50 million).<ref name="Mankins"> {{Webarchive|url=https://web.archive.org/web/20140419224918/http://www.nss.org/settlement/ssp/library/2000-testimony-JohnMankins.htm |date=2014-04-19 }} U.S. House Subcommittee on Space and Aeronautics Committee on Science, Sep 7, 2000</ref> Several reports were published investigating the engineering feasibility of such a project. They include:
* State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities<ref></ref>

* Student Participation<ref></ref>
* Potential of Laser for SBSP Power Transmission<ref></ref> * Resource Requirements (Critical Materials, Energy, and Land)<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-ResourceRequirements.pdf|title=Satellite Power System (SPS) Resource Requirements (Critical Materials, Energy, and Land). HCP/R-4024-02, October 1978.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208220252/http://www.nss.org/settlement/ssp/library/1978DOESPS-ResourceRequirements.pdf|url-status=dead}}</ref>
* International Agreements<ref></ref><ref></ref> * Financial/Management Scenarios<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-FinancialManagementScenarios(Vajk).pdf|title=Satellite Power System (SPS) Financial/Management Scenarios. Prepared by J. Peter Vajk. HCP/R-4024-03, October 1978. 69 pages|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208220033/http://www.nss.org/settlement/ssp/library/1978DOESPS-FinancialManagementScenarios(Vajk).pdf|url-status=dead}}</ref><ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-FinancialManagementScenarios(Kierolff).pdf|title=Satellite Power System (SPS) Financial/Management Scenarios. Prepared by Herbert E. Kierulff. HCP/R-4024-13, October 1978. 66 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208223021/http://www.nss.org/settlement/ssp/library/1978DOESPS-FinancialManagementScenarios(Kierolff).pdf|url-status=dead}}</ref>
* Centralization/Decentralization<ref></ref> * Public Acceptance<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-PublicAcceptance.pdf|title=Satellite Power System (SPS) Public Acceptance. HCP/R-4024-04, October 1978. 85 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208222459/http://www.nss.org/settlement/ssp/library/1978DOESPS-PublicAcceptance.pdf|url-status=dead}}</ref>
* Mapping of Exclusion Areas For Rectenna Sites<ref></ref> * State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-StateAndLocalRegulations.pdf|title=Satellite Power System (SPS) State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities. HCP/R-4024-05, October 1978. 92 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208222317/http://www.nss.org/settlement/ssp/library/1978DOESPS-StateAndLocalRegulations.pdf|url-status=dead}}</ref>
* Economic and Demographic Issues Related to Deployment<ref></ref> * Student Participation<ref>{{Cite web |url=http://www.nss.org/settlement/ssp/library/1978DOESPS-StudentParticipation.pdf |title=Satellite Power System (SPS) Student Participation. HCP/R-4024-06, October 1978. 97 pages. |access-date=2009-02-20 |archive-date=2013-12-08 |archive-url=https://web.archive.org/web/20131208220426/http://www.nss.org/settlement/ssp/library/1978DOESPS-StudentParticipation.pdf |url-status=dead }}</ref>
* Potential of Laser for SBSP Power Transmission<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-PotentialOfLaserForSPSPowerTransmission.pdf|title=Potential of Laser for SPS Power Transmission. HCP/R-4024-07, October 1978. 112 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208221443/http://www.nss.org/settlement/ssp/library/1978DOESPS-PotentialOfLaserForSPSPowerTransmission.pdf|url-status=dead}}</ref>
* Some Questions and Answers<ref></ref>
* International Agreements<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-InternationalAgreements(Christol).pdf|title=Satellite Power System (SPS) International Agreements. Prepared by Carl Q. Christol. HCP-R-4024-08, October 1978. 283 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208222703/http://www.nss.org/settlement/ssp/library/1978DOESPS-InternationalAgreements(Christol).pdf|url-status=dead}}</ref><ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-InternationalAgreements(Grove).pdf|title=Satellite Power System (SPS) International Agreements. Prepared by Stephen Grove. HCP/R-4024-12, October 1978. 86 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208220843/http://www.nss.org/settlement/ssp/library/1978DOESPS-InternationalAgreements(Grove).pdf|url-status=dead}}</ref>
* Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers<ref></ref>
* Public Outreach Experiment<ref></ref> * Centralization/Decentralization<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-CentralizationDecentralization.pdf|title=Satellite Power System (SPS) Centralization/Decentralization. HCP/R-4024-09, October 1978. 67 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208220132/http://www.nss.org/settlement/ssp/library/1978DOESPS-CentralizationDecentralization.pdf|url-status=dead}}</ref>
* Mapping of Exclusion Areas For Rectenna Sites<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-MappingOfExclusionAreasForRectennaSites.pdf|title=Satellite Power System (SPS) Mapping of Exclusion Areas For Rectenna Sites. HCP-R-4024-10, October 1978. 117 pages.|access-date=2009-02-20|archive-date=2014-02-24|archive-url=https://web.archive.org/web/20140224074932/http://www.nss.org/settlement/ssp/library/1978DOESPS-MappingOfExclusionAreasForRectennaSites.pdf|url-status=dead}}</ref>
* Power Transmission and Reception Technical Summary and Assessment <ref>http://www.nss.org/settlement/ssp/library/1981NASASPS-PowerTransmissionAndReception.pdf
* Economic and Demographic Issues Related to Deployment<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1978DOESPS-EconomicAndDemographicIssues.pdf|title=Economic and Demographic Issues Related to Deployment of the Satellite Power System (SPS). ANL/EES-TM-23, October 1978. 71 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208221703/http://www.nss.org/settlement/ssp/library/1978DOESPS-EconomicAndDemographicIssues.pdf|url-status=dead}}</ref>
* Some Questions and Answers<ref>{{Cite web |url=http://www.nss.org/settlement/ssp/library/1980DOESPS-QuestionsAndAnswersAboutSPS.pdf |title=Some Questions and Answers About the Satellite Power System (SPS). DOE/ER-0049/1, January 1980. 47 pages. |access-date=2009-02-20 |archive-date=2013-12-08 |archive-url=https://web.archive.org/web/20131208220102/http://www.nss.org/settlement/ssp/library/1980DOESPS-QuestionsAndAnswersAboutSPS.pdf |url-status=dead }}</ref>
* Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1980NASASPS-LaserStudies-MeteorologicalEffects.pdf|title=Satellite Power Systems (SPS) Laser Studies: Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers for the SPS. NASA Contractor Report 3347, November 1980. 143 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208222651/http://www.nss.org/settlement/ssp/library/1980NASASPS-LaserStudies-MeteorologicalEffects.pdf|url-status=dead}}</ref>
* Public Outreach Experiment<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1980DOESPS-PublicOutreachExperiment.pdf|title=Satellite Power System (SPS) Public Outreach Experiment. DOE/ER-10041-T11, December 1980. 67 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208222311/http://www.nss.org/settlement/ssp/library/1980DOESPS-PublicOutreachExperiment.pdf|url-status=dead}}</ref>
* Power Transmission and Reception Technical Summary and Assessment<ref>http://www.nss.org/settlement/ssp/library/1981NASASPS-PowerTransmissionAndReception.pdf {{Webarchive|url=https://web.archive.org/web/20131208222600/http://www.nss.org/settlement/ssp/library/1981NASASPS-PowerTransmissionAndReception.pdf |date=2013-12-08 }}
"Satellite Power System Concept Development and Evaluation Program: Power Transmission and Reception Technical Summary and Assessment" NASA Reference Publication 1076, July 1981. 281 pages.</ref> "Satellite Power System Concept Development and Evaluation Program: Power Transmission and Reception Technical Summary and Assessment" NASA Reference Publication 1076, July 1981. 281 pages.</ref>
* Space Transportation<ref></ref> * Space Transportation<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1981NASASPS-SpaceTransportation.pdf|title=Satellite Power System Concept Development and Evaluation Program: Space Transportation. NASA Technical Memorandum 58238, November 1981. 260 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208215755/http://www.nss.org/settlement/ssp/library/1981NASASPS-SpaceTransportation.pdf|url-status=dead}}</ref>

==== Discontinuation ====

The project was not continued with the change in administrations after the ]. The ] concluded that "Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture."<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1981-OTA-SolarPowerSatellites.pdf|title=Solar Power Satellites. Office of Technology Assessment, August 1981. 297 pages.|access-date=2009-02-20|archive-date=2013-12-08|archive-url=https://web.archive.org/web/20131208220917/http://www.nss.org/settlement/ssp/library/1981-OTA-SolarPowerSatellites.pdf|url-status=dead}}</ref>


In 1997, NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that the "US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO '''' transportation down dramatically. This is, of course, an absolute requirement of space solar power."<ref>{{Cite web|url=http://www.nss.org/settlement/ssp/library/1997-Mankins-FreshLookAtSpaceSolarPower.pdf|title=A Fresh Look at Space Solar Power: New Architectures, Concepts, and Technologies. John C. Mankins. International Astronautical Federation IAF-97-R.2.03. 12 pages.|access-date=2009-02-20|archive-date=2017-10-26|archive-url=https://web.archive.org/web/20171026141520/http://www.nss.org/settlement/ssp/library/1997-Mankins-FreshLookAtSpaceSolarPower.pdf|url-status=dead}}</ref>
The project was not continued with the change in administrations after the 1980 US Federal elections.


Conversely, ] of NASA claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Worden referred to possible solutions as speculative and not available for decades at the earliest.<ref name="ReferenceA">{{cite web|title= Dr. Pete Worden on thespaceshow|url= http://www.thespaceshow.com/detail.asp?q=1127|publisher= thespaceshow.com|date= 23 March 2009|url-status= dead|archive-url= https://web.archive.org/web/20120707205702/http://www.thespaceshow.com/detail.asp?q=1127|archive-date= 7 July 2012}}</ref>
The ]<ref></ref> concluded
<blockquote> Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture.</blockquote>


On November 2, 2012, China proposed a space collaboration with India that mentioned SBSP, "may be Space-based Solar Power initiative so that both India and China can work for long term association with proper funding along with other willing space faring nations to bring space solar power to earth."<ref>{{cite news| url=https://timesofindia.indiatimes.com/india/China-proposes-space-collaboration-with-India/articleshow/17066537.cms | archive-url=https://web.archive.org/web/20130523152006/http://articles.timesofindia.indiatimes.com/2012-11-02/india/34877401_1_space-solar-power-space-collaboration-v-ponraj | url-status=live | archive-date=2013-05-23 | work=] | title=China proposes space collaboration with India |date=2012-11-02}}</ref>
In 1997 NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility.<ref></ref> In assessing "What has changed" since the DOE study, NASA asserted that:


=== Exploratory Research and Technology program ===
<blockquote>US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO '''' transportation down dramatically. This is, of course, an absolute requirement of space solar power.</blockquote>


{{main|Space Solar Power Exploratory Research and Technology program}}
Conversely, Dr. Pete Worden claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Dr. Worden referred to possible solutions as speculative, and that would not be available for decades at the earliest.<ref name="ReferenceA">Dr. Pete Worden on thespaceshow.com in the edition of the 23rd of March, 2009</ref>


] ]


In 1999, NASA initiated its Space Solar Power Exploratory Research and Technology program (SERT) for the following purposes:
=== SERT ===
In 1999, NASA's ] (SERT) (budget 22 millions $)<ref name="Mankins" /> was initiated for the following purposes:


* Perform design studies of selected flight demonstration concepts. * Perform design studies of selected flight demonstration concepts.
Line 60: Line 72:
* Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications. * Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
* Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative. * Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
* Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements. * Construct technology development and demonstration roadmaps for critical space solar power (SSP) elements.


SERT went about developing a solar power satellite (SPS) concept for a future ] space power system, to provide electrical power by converting the Sun’s energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an ] ] ] structure with ] or ] ]s to convert ] into electricity. The program looked both at systems in ] and ]. SERT went about developing a solar power satellite (SPS) concept for a future ] space power system, to provide electrical power by converting the Sun's energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an ] ] ] structure with concentrator lenses or ] ]s to convert ] into electricity. The program looked both at systems in ] and ]. Some of SERT's conclusions:


* The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
Some of SERT's conclusions:

* The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
* The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic. * The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic.
* Renewable energy is a compelling approach, both philosophically and in engineering terms. * Renewable energy is a compelling approach, both philosophically and in engineering terms.
Line 73: Line 83:
* Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin. * Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin.
* Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches. * Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
* The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of much lower cost access to space than has been available), however, the same can be said of many other advanced power technologies options. * The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of much lower cost access to space than has been available); however, the same can be said of many other advanced power technologies options.
* Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.<ref> James E. Dudenhoefer and Patrick J. George, NASA ], Cleveland, Ohio</ref> * Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.<ref>Space Solar Power Satellite Technology Development at the Glenn Research Center—An Overview. James E. Dudenhoefer and Patrick J. George, NASA ], Cleveland, Ohio.</ref>
* ] in the range of $100-$200 per kilogram of payload to low-Earth orbit are needed if SPS are to be economically viable.<ref name="Mankins" /> * ] in the range of $100–$200 per kilogram of payload from ] to ] are needed if SPS is to be economically viable.<ref name="Mankins" />


=== Japan Aerospace Exploration Agency ===
== Advantages ==
The May 2014 ] Spectrum magazine carried a lengthy article "It's Always Sunny in Space" by Susumu Sasaki.<ref>{{cite web|url=https://spectrum.ieee.org/how-japan-plans-to-build-an-orbital-solar-farm|title=How Japan Plans to Build an Orbital Solar Farm|date=24 April 2014}}</ref> The article stated, "It's been the subject of many previous studies and the stuff of sci-fi for decades, but space-based solar power could at last become a reality—and within 25 years, according to a proposal from researchers at the ]-based ] (JAXA)."
The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power.


JAXA announced on 12 March 2015 that they wirelessly beamed 1.8 kilowatts 50 meters to a small receiver by converting electricity to microwaves and then back to electricity. This is the standard plan for this type of power.<ref name="ATarantola">{{cite magazine|first=Andrew | last=Tarantola| title=Scientists make strides in beaming solar power from space |date=12 March 2015 |magazine=Engadget |volume=162 |issue=3856 |pages=857–861 |format=PDF |url=https://www.engadget.com/2015/03/12/scientists-make-strides-in-beaming-solar-power-from-space/}}</ref><ref name="PKT">{{Cite web|url=https://www.thenews.com.pk/latest/2372-japan-space-scientists-make-wireless-energy-breakthrough|title=Japan space scientists make wireless energy breakthrough|website=www.thenews.com.pk}}</ref> On 12 March 2015 Mitsubishi Heavy Industries demonstrated transmission of 10 kilowatts (kW) of power to a receiver unit located at a distance of 500 meters (m) away.<ref>{{Cite web|url=http://www.mhi-global.com/news/story/1503121879.html|title=MHI Successfully Completes Ground Demonstration Testing of Wireless Power Transmission Technology for SSPS|date=12 March 2015|access-date=20 March 2015|archive-date=15 March 2015|archive-url=https://web.archive.org/web/20150315115134/http://www.mhi-global.com/news/story/1503121879.html|url-status=dead}}</ref>
* There is no ] in space, so the collecting surfaces could receive much more intense sunlight, unobstructed by weather.
* A satellite could be illuminated over 99% of the time, and be in Earth's ] on only 75 minutes per night at the spring and fall ]es.<ref>{{Cite book|date=August 1981| title = Solar Power Satellites| page=66| place = Washington, D.C.| publisher = Congress of the U.S., Office of Technology Assessment| id = LCCN 81600129}}</ref>
* Relatively quick redirecting of power directly to areas that need it most.
* Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of ]. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth's surface.
* Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar ], generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most.<ref name="ReferenceB"/>
* Elimination of ] concerns, since the collecting satellite would reside well outside of any atmospheric gasses, ] cover, wind, and other weather events.
* Elimination of ] and ] interference.
* Redirectable power transmission: A collecting satellite could possibly direct power on demand to different surface locations based on geographical ] or ] power needs.


== Advantages and disadvantages ==
== Disadvantages ==
The SBSP concept also has a number of problems.


=== Advantages ===
* The space environment is hostile; panels suffer about 10 times the degradation they would on Earth.<ref>In space, panels suffer rapid erosion due to high energy particles, whereas on Earth, commercial panels degrade at a rate around 0.25% a year.</ref> System lifetimes on the order of a decade would be expected, which makes it difficult to produce enough power to be economical.
* ] are a major hazard to large objects in space, and SBSP systems have been singled out as a particularly hazardous activity.<ref>"Some of the most environmentally dangerous activities in space include large structures such as those considered in the late-1970s for building solar power stations in Earth orbit.</ref>
* Only about half the power generated by the SSP would be delivered to the grid, once all losses are factored in. These losses are on the same order as modern fossil fuel plants.


The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power:
== Design ==
* It is always ] in space and full sun.
].]]
* Collecting surfaces could receive much more intense sunlight, owing to the lack of obstructions such as ], ]s, dust and other weather events. Consequently, the intensity in orbit is approximately 144% of the maximum attainable intensity on Earth's surface.{{citation needed|date=March 2013}}
Space-based solar power essentially consists of three elements:
* A satellite could be illuminated over 99% of the time and be in Earth's ] a maximum of only 72 minutes per night at the spring and fall equinoxes at local midnight.<ref>{{Cite book|date=August 1981| title = Solar Power Satellites| page=66| place = Washington, D.C.| publisher = Congress of the U.S., Office of Technology Assessment| lccn = 81600129}}</ref> Orbiting satellites can be exposed to a consistently high degree of solar ], generally for 24 hours per day, whereas earth surface solar panels currently collect power for an average of 29% of the day.<ref name="ReferenceB">Collection at Earth's ] can take place for 24 hours per day, but there are very small loads demanded at the poles.</ref>
* Power could be relatively quickly redirected directly to areas that need it most. A collecting satellite could possibly direct power on demand to different surface locations based on geographical ] or ] power needs.
* Reduced ] and ] interference.
* SBSP does not emit greenhouse gases unlike oil, gas, ethanol, and coal plants. Space based solar power also does not depend on or compete with scarce fresh water resources, unlike coal and nuclear plants. <ref>{{Cite web |title=Space Solar Power Info: Limitless clean energy from space – NSS |date=11 August 2017 |url=https://nss.org/space-solar-power-info/ |access-date=2024-05-03 |language=en-US}}</ref>
* SBSP generates forty times more than solar panels, and bring almost zero percent of hazardous waste to our environment. It also allows for electricity to be generated continuously, twenty four hours a day, ninety nine percent of the year. <ref>{{Cite web |title=Is Space-Based Solar Power Our Future? (2024) {{!}} GreenMatch |url=https://www.greenmatch.co.uk/blog/2020/02/space-based-solar-power |access-date=2024-05-03 |website=GreenMatch.co.uk |language=en-GB}}</ref>
* If the clean energy that is provided from space-based solar power account for just five percent of our national energy consumption, our carbon footprint would be significantly reduced. <ref>{{Cite web |last=Steitz |first=David |date=2024-01-19 |title=NASA study: clean, space-based solar power beaming is possible |url=https://spacenews.com/nasa-study-clean-space-based-solar-power-beaming-possible/ |access-date=2024-05-03 |website=SpaceNews |language=en-US}}</ref>


=== Disadvantages ===
* a means of collecting solar power in space, for example via ]s or a ]
* a means of transmitting power to earth, for example via microwave or laser
* a means of receiving power on earth, for example via a microwave antenna (rectenna)


The SBSP concept also has a number of problems:
The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as ]s and ].
* The large cost of launching a satellite into space. For 6.5&nbsp;kg/kW, the cost to place a power satellite in geosynchronous orbit (GEO) cannot exceed $200/kg if the power cost is to be competitive.
* Microwave optic requires gigawatt scale to compensate for ] beam spreading. Typically a 1&nbsp;km disk in geosynchronous orbit transmitting at 2.45&nbsp;GHz spreads out to 10&nbsp;km at Earth distance.<ref>{{cite web|url= https://www.esa.int/Enabling_Support/Space_Engineering_Technology/SOLARIS/Space-Based_Solar_Power_overview |website= esa.int |title= Space-Based Solar Power overview |date=2022-08-08 |access-date=2024-04-03}}</ref>
* Inability to constrain power transmission inside tiny beam angles. For example, a beam of 0.002 degrees (7.2 arc seconds) is required to stay within a one kilometer receiving antenna target from geostationary altitude. The most advanced directional ] systems as of 2019 spread their ] across at least 0.9 arc degrees.<ref>{{cite journal |last1=Shen |first1=G. |last2=Liu |first2=Y. |last3=Sun |first3=G. |last4=Zheng |first4=T. |last5=Zhou |first5=X. |last6=Wang |first6=A. |title=Suppressing Sidelobe Level of the Planar Antenna Array in Wireless Power Transmission |journal=IEEE Access |date=2019 |volume=7 |pages=6958–6970 |doi=10.1109/ACCESS.2018.2890436 |issn=2169-3536|doi-access=free |bibcode=2019IEEEA...7.6958S }}</ref><ref>{{cite journal |last1=Wang |first1=Wen-Qin |title=Retrodirective Frequency Diverse Array Focusing for Wireless Information and Power Transfer |journal=IEEE Journal on Selected Areas in Communications |date=2019 |volume=37 |issue=1 |pages=61–73 |doi=10.1109/JSAC.2018.2872360 |s2cid=56594774 |issn=0733-8716}}</ref><ref>{{cite journal |last1=Shinohara |first1=Naoki |title=Beam Control Technologies With a High-Efficiency Phased Array for Microwave Power Transmission in Japan |journal=Proceedings of the IEEE |date=June 2013 |volume=101 |issue=6 |pages=1448–1463 |doi=10.1109/JPROC.2013.2253062 |s2cid=9091936 |doi-access=free |hdl=2433/174333 |hdl-access=free }}</ref><ref>{{cite arXiv |last1=Fartookzadeh |first1=Mahdi |title=On the Time-Range Dependency of the Beampatterns Produced by Arbitrary Antenna Arrays: Discussions on the Misplaced Expectations from Frequency Diverse Arrays |date=7 March 2019 |class=physics.class-ph |eprint=1903.03508}} {{bibcode|2019arXiv190303508F}}</ref>
* Inaccessibility: Maintenance of an earth-based solar panel is relatively simple, but construction and maintenance on a solar panel in space would typically be done telerobotically. In addition to cost, astronauts working in GEO are exposed to unacceptably high radiation dangers and risk and cost about one thousand times more than the same task done telerobotically.
* The space environment is hostile; PV panels (if used) suffer about eight times the degradation they would on Earth (except at orbits that are protected by the magnetosphere).<ref>In space, panels suffer rapid erosion from high energy particles, {{webarchive|url=https://web.archive.org/web/20110929152905/http://www.solarstorms.org/Svulnerability.html |date=2011-09-29 }} whereas on Earth, commercial panels degrade at a rate around 0.25% a year.</ref>
* ] is a major hazard to large objects in space, particularly for large structures such as SBSP systems in transit through the debris below 2000&nbsp;km. Already in 1978, astrophysicist ] warned against a self-propagating collision cascade during the assembly of the SPS modules in LEO, which is now known as ].<ref>{{Cite web |date=2009-03-08 |title=The Kessler Syndrome |url=http://webpages.charter.net/dkessler/files/KesSym.html |url-status=dead |archive-url=https://web.archive.org/web/20180622033619/http://webpages.charter.net/dkessler/files/KesSym.html |archive-date=2018-06-22 |access-date=2010-05-26}}</ref><ref>{{Cite journal |last=Thanei |first=Luca |date=August 2024 |title=The Solar Power Satellite and NASA's Changing Perception of Near-Earth Space, 1976–1982 |journal=] |volume=31 |issue=3 |pages=9–24}}</ref> Collision risk is much reduced in GEO since all the satellites are moving in the same direction at very close to the same speed.
* The broadcast frequency of the microwave downlink (if used) would require isolating the SBSP systems away from other satellites. GEO space is already well used and would require coordinating with the ].<ref>{{cite web | url=http://www.ieice.org/proceedings/EMC09/pdf/21Q1-4.pdf | title=Space Solar Power Satellite/Station and the Politics | work=EMC'09/Kyoto | date=2009 | access-date=August 7, 2021 | author=Matsumoto, Hiroshi|archive-url=https://web.archive.org/web/20190808024723/https://www.ieice.org/proceedings/EMC09/pdf/21Q1-4.pdf|archive-date=August 8, 2019}}</ref>
* The large size and corresponding cost of the receiving station on the ground. The cost has been estimated at a billion dollars for 5 GW by SBSP researcher ].
* Energy losses during several phases of conversion from photons to electrons to photons back to electrons.<ref>{{Cite web |date=2012-10-04 |title=Elon Musk on SpaceX, Tesla, and More |url=https://www.popularmechanics.com/technology/a8101/elon-musk-on-spacex-tesla-and-why-space-solar-power-must-die-13386162/ |access-date=2023-06-15 |website=Popular Mechanics |language=en-US}}</ref><ref>{{Cite book |last=Swan |first=Philip |title=2019 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW) |chapter=Wireless Power At-A-Distance Technology – A Strategy for Nurturing Ecosystem Development |date=2019 |chapter-url=https://ieeexplore.ieee.org/document/9030683 |journal=Institute of Electrical and Electronics Engineers |publisher=IEEE |pages=99–104 |doi=10.1109/WoW45936.2019.9030683 |isbn=978-1-5386-7514-4|s2cid=212703930 }}</ref>
* ] disposal in space power systems is difficult to begin with, but becomes intractable when the entire spacecraft is designed to absorb as much solar radiation as possible. Traditional ] systems such as radiative vanes may interfere with solar panel occlusion or power transmitters.
* Decommissioning costs: The cost of deorbiting the satellites at the end of their ] to prevent them from exacerbating the orbital ] problem due to impacts with asteroidal, cometary, and planetary debris<ref>{{Citation |last1=Zolensky |first1=Michael |title=Flux of Extraterrestrial Materials |date=2006-07-01 |url=http://dx.doi.org/10.2307/j.ctv1v7zdmm.46 |work=Meteorites and the Early Solar System II |pages=869–888 |access-date=2023-06-15 |publisher=University of Arizona Press |last2=Bland |first2=Phil |last3=Brown |first3=Peter |last4=Halliday |first4=Ian|doi=10.2307/j.ctv1v7zdmm.46 }}</ref> is likely to be significant. While the future cost of imparting ] is difficult to estimate, the amount of Delta-V that must be imparted to transfer a satellite from GEO to GTO is 1472 m/s<sup>2</sup>. If, upon reentry, the disintegrating satellite would release hazardous chemicals into the Earth's atmosphere, then the additional expenses of disassembling the satellite and deorbiting the environmentally hazardous components within a space vehicle with ] capabilities must be factored into the decommissioning costs.
* Since these systems would be in space, they obviously would not be able to be controlled hands-on. Researchers, will need to create a way to maintain these systems autonomously, which could create some technical issues.<ref>{{Cite web |date=2024-01-11 |title=New Study Updates NASA on Space-Based Solar Power - NASA |url=https://www.nasa.gov/organizations/otps/space-based-solar-power-report/ |access-date=2024-05-06 |language=en-US}}</ref>
* Research has also shown that an increase in population can increase congestion and ultimately could cause pieces of orbital debris, which was concluded from a test China had done with their satellite. <ref>{{Cite journal |last=Caton Mr. |first=Jeffery L. |date=2015-01-04 |title=Space-Based Solar Power: A Technical, Economic, and Operational Assessment |url=https://press.armywarcollege.edu/cgi/viewcontent.cgi?article=1456&context=monographs |journal=US Army War College}}</ref>


== Design ==
Two basic methods of conversion have been studied: ] (PV) and ] (SD). Most analyses of SBSP have focused on photovoltaic conversion (commonly known as “]”). Photovoltaic conversion uses ] cells to directly convert photons into electrical power.
].]]


Space-based solar power essentially consists of three elements:<ref name="DOE-SBSP" />
] was proposed early on as a means to transfer energy from collection to the Earth's surface, using either microwave or laser radiation at a variety of ].

# collecting solar energy in space with reflectors or inflatable mirrors onto ]s or heaters for thermal systems
# ] to Earth via ] or ]
# receiving power on Earth via a ], a microwave antenna

The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as ]s and ]. Two basic methods of conversion have been studied: ] (PV) and ] (SD). Most analyses of SBSP have focused on photovoltaic conversion using solar cells that directly convert sunlight into electricity. Solar dynamic uses mirrors to concentrate light on a boiler. The use of solar dynamic could reduce mass per watt. ] was proposed early on as a means to transfer energy from collection to the Earth's surface, using either microwave or laser radiation at a variety of frequencies.


=== Microwave power transmission === === Microwave power transmission ===
] demonstrated in 1964, during ]'s ] News program, a microwave-powered model ] that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a ] ] program that beamed 30 ] of power over a distance of {{convert|1|mi|km|adj=on}} at 84% efficiency.<ref name="Brown">{{cite journal |doi= 10.1109/TMTT.1984.1132833 |first= W. C.| last= Brown.| title= The History of Power Transmission by Radio Waves | journal= ] |volume= 32| date=September 1984 |pages= 1230 | issue= Volume: 32, Issue: 9 On page(s): 1230- 1242 + ISSN: 0018-9480 |url=http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1132833 | bibcode=1984ITMTT..32.1230B}}</ref>


] demonstrated in 1964, during ]'s ] News program, a microwave-powered model ] that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a ] ] program that beamed 30 ] of power over a distance of {{convert|1|mi|km}} at 9.6% efficiency.<ref>{{cite book |last1=Dickenson |first1=R.M. |title=Evaluation of a Microwave High-Power Reception-Conversion Array for Wireless Power Transmission |date=1 September 1975 |publisher=NASA Jet Propulsion Laboratory |pages=8–24 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760004119.pdf |access-date=2 June 2019 |format=JPL Technical Memorandum 33-741 |quote=Because of the small size of the array relative to the 26-m-diameter antenna tubular beam, only about 11.3% of the klystron transmitter output is incident on the array (see Fig. 12) and is thus available for collection and conversion to DC output.}}</ref><ref name="Brown">{{cite journal |doi=10.1109/TMTT.1984.1132833 |title=The History of Power Transmission by Radio Waves |journal=IEEE Transactions on Microwave Theory and Techniques |volume=32 |issue=9 |pages=1230–1242 |year=1984 |last1=Brown |first1=W.C. |bibcode=1984ITMTT..32.1230B |s2cid=73648082 }}</ref>
Microwave power transmission of tens of kilowatts has been well proven by existing tests at ] in California (1975) <ref name="Brown"/><ref></ref><ref></ref> and Grand Bassin on ] (1997).<ref> 48th International Astronautical Congress, Turin, Italy, 6–10 October 1997 - IAF-97-R.4.08 J. D. Lan Sun Luk, A. Celeste, P. Romanacce, L. Chane Kuang Sang, J. C. Gatina - University of La Réunion - Faculty of Science and Technology.</ref>


Microwave power transmission of tens of kilowatts has been well proven by existing tests at ] in California (1975)<ref name="Brown"/><ref>{{cite web|url=https://www.youtube.com/watch?v=sy1vqRT-vqI |archive-url=https://ghostarchive.org/varchive/youtube/20211219/sy1vqRT-vqI |archive-date=2021-12-19 |url-status=live|title=Wireless Power Transmission 34kw over 1 mile at 82.5% efficiency Goldstone 1975|date=13 March 2008|via=YouTube}}{{cbignore}}</ref><ref>{{Cite web|url=http://www.sspi.gatech.edu/wptshinohara.pdf|title=Wireless Power Transmission for Solar Power Satellite (SPS) (Second Draft by N. Shinohara), Space Solar Power Workshop, Georgia Institute of Technology}}</ref> and Grand Bassin on ] (1997).<ref> {{webarchive|url=https://web.archive.org/web/20051023080942/http://www2.univ-reunion.fr/~lcks/Old_Version/PubIAF97.htm |date=2005-10-23 }} 48th International Astronautical Congress, Turin, Italy, 6–10 October 1997&nbsp;– IAF-97-R.4.08 J. D. Lan Sun Luk, A. Celeste, P. Romanacce, L. Chane Kuang Sang, J. C. Gatina&nbsp;– University of La Réunion&nbsp;– Faculty of Science and Technology.</ref>
]


]
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountain top in Maui and the main island of Hawaii (92 miles away), by a team under John C. Mankins.<ref>.</ref><ref> by Loretta Hidalgo, September 12, 2008</ref>

Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it is demonstrated by the upcoming Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" to be held in the 2010 ] Symposium on Antennas and Propagation.<ref></ref>
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountaintop in Maui and the island of Hawaii (92 miles away), by a team under ].<ref> {{Webarchive|url=https://web.archive.org/web/20100620042655/http://nss.org/news/releases/pc20080912.html |date=2010-06-20 }}.</ref><ref> by Loretta Hidalgo, September 12, 2008</ref> Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it was demonstrated by the Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" held during the 2010 ] Symposium on Antennas and Propagation.<ref>{{Cite web|url=http://www.apsursi2010.org/?m=page&id=47|title=2010 APS/URSI|date=July 26, 2009|archive-url=https://web.archive.org/web/20090726090427/http://www.apsursi2010.org/?m=page&id=47|archive-date=2009-07-26}}</ref> In 2013, a useful overview was published, covering technologies and issues associated with microwave power transmission from space to ground. It includes an introduction to SPS, current research and future prospects.<ref name= Sasaki>{{cite journal |doi=10.1109/JPROC.2013.2246851 |title=Microwave Power Transmission Technologies for Solar Power Satellites |journal=Proceedings of the IEEE |volume=101 |issue=6 |pages=1438 |year=2013 |last1=Sasaki |first1=Susumu |last2=Tanaka |first2=Koji |last3=Maki |first3=Ken-Ichiro |s2cid=23479022 }}</ref> Moreover, a review of current methodologies and technologies for the design of antenna arrays for microwave power transmission appeared in the Proceedings of the IEEE.<ref name= MASSA>{{cite journal |doi=10.1109/JPROC.2013.2245491 |title=Array Designs for Long-Distance Wireless Power Transmission: State-of-the-Art and Innovative Solutions |journal=Proceedings of the IEEE |volume=101 |issue=6 |pages=1464 |year=2013 |last1=Massa |first1=Andrea |last2=Oliveri |first2=Giacomo |last3=Viani |first3=Federico |last4=Rocca |first4=Paolo |s2cid=2990114 }}</ref>


=== Laser power beaming === === Laser power beaming ===
] power beaming was envisioned by some at NASA as a stepping stone to further industrialization of space. In the 1980s, researchers at NASA worked on the potential use of lasers for space-to-space power beaming, focusing primarily on the development of a solar-powered laser. In 1989 it was suggested that power could also be usefully beamed by laser from Earth to space. In 1991 the SELENE project (SpacE Laser ENErgy) had begun, which included the study of laser power beaming for supplying power to a lunar base. The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project ended in 1993 before reaching a space-based demonstration.<ref> NASA Glenn Research Center</ref>


] power beaming was envisioned by some at NASA as a stepping stone to further industrialization of space. In the 1980s, researchers at NASA worked on the potential use of lasers for space-to-space power beaming, focusing primarily on the development of a solar-powered laser. In 1989, it was suggested that power could also be usefully beamed by laser from Earth to space. In 1991, the SELENE project (SpacE Laser ENErgy) had begun, which included the study of ] for supplying power to a lunar base. The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project ended in 1993 before reaching a space-based demonstration.<ref> {{webarchive|url=https://web.archive.org/web/20061117234426/http://powerweb.grc.nasa.gov/pvsee/programs/pvlaser_overview.html |date=2006-11-17 }} NASA Glenn Research Center</ref>
In 1988 the use of an Earth-based laser to power an electric thruster for space propulsion was proposed by Grant Logan, with technical details worked out in 1989. He proposed using diamond solar cells operating at 600 degrees to convert ] laser light, a technology that has yet to be demonstrated even in the laboratory.

=== Laser Solar Satellites ===
Laser Solar Satellites are smaller in size, meaning that they have to work as a group with other similar satellites. There are many pros to Laser Solar Satellites, specifically regarding their lower overall costs in comparison to other satellites. While the cost is lower than other satellites, there are various safety concerns, and other concerns regarding this satellite. <ref>{{Cite web |title=Space-Based Solar Power |url=https://www.energy.gov/space-based-solar-power |access-date=2024-03-12 |website=Energy.gov |language=en}}</ref> Laser-emitting solar satellites only need to venture about 400 km into space, but because of their small generation capacity, hundreds or thousands of laser satellites would need to be launched in order to create a sustainable impact. A single satellite launch can range from fifty to four hundred million dollars. Lasers could be helpful for the energy from the sun harvested in space, to be returned back to Earth in order for terrestrial power demands to be met. <ref>{{Cite web |last=Cohen |first=Ariel |title=How Space Lasers Could Soon Beam Clean Power Down To Earth |url=https://www.forbes.com/sites/arielcohen/2021/03/29/space-lasers-the-truth/ |access-date=2024-05-03 |website=Forbes |language=en}}</ref>


=== Orbital location === === Orbital location ===
The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit; other space-based power stations have much longer start-up times before they are producing nearly continuous power.


The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit, LEO requires several satellites before they are producing nearly continuous power.
A collection of LEO (]) space power stations has been proposed as a precursor to GEO (]) space-based solar power.<ref>{{Cite book

| last1=Komerath
Power beaming from ] by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1 km diameter transmitting antenna and a 10&nbsp;km diameter receiving rectenna for a microwave beam at ]. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased ] and even potential beam blockage by rain or water droplets. Because of the ], it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.{{Original research inline|date=March 2017}}
| first1=N.M

| last2=Boechler
A collection of LEO (]) space power stations has been proposed as a precursor to GEO (]) space-based solar power.<ref>{{Cite book | last1=Komerath | first1=N.M | last2=Boechler | first2=N. | title=The Space Power Grid | publisher=57th International Astronautical Federation Congress | place=Valencia, Spain | id=IAC-C3.4.06 | date=October 2006 }}</ref>
| first2=N.
| title=The Space Power Grid
| publisher=57th International Astronautical Federation Congress
| place=Valencia, Spain
| id=IAC-C3.4.06
| month=October
| year=2006
}}
</ref>


=== Earth-based receiver === === Earth-based receiver ===

The Earth-based ] would likely consist of many short ] antennas connected via ]s. Microwaves broadcasts from the satellite would be received in the dipoles with about 85% efficiency.<ref></ref> With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity is also considerably greater. Rectennas would likely be multiple kilometers across.
The Earth-based ] would likely consist of many short ]s connected via ]s. Microwave broadcasts from the satellite would be received in the dipoles with about 85% efficiency.<ref>{{Cite web|url=https://www.hq.nasa.gov/webaccess/CommSpaceTrans/SpaceCommTransSec38/CommSpacTransSec38.html|title=CommSpacTransSec38.html|website=www.hq.nasa.gov}}</ref> With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity are also considerably greater. Rectennas would likely be several kilometers across.


=== In space applications === === In space applications ===
A laser sbsp could also power a base or vehicules on the surface of the moon or mars, saving on mass costs to land the power source.A spacecraft or another satellite could also be powered by the same means.<ref>{{cite web | url=http://www.nss.org/settlement/ssp/library/1989-SecondBeamedSpacePowerWorkshop.pdf | title=Second Beamed Space-Power Workshop | publisher=Nasa | date=1989 | pages=near page 290}}</ref>


A laser SBSP could also power a base or vehicles on the surface of the Moon or Mars, saving on mass costs to land the power source. A spacecraft or another satellite could also be powered by the same means. In a 2012 report presented to NASA on space solar power, the author mentions another potential use for the technology behind space solar power could be for solar electric propulsion systems that could be used for interplanetary human exploration missions.<ref>{{cite web|last=Mankins|first=John|title=SPS-ALPHA: The First Practical Solar Power Satellite via Arbitrarily Large Phased Array|url=http://www.nss.org/settlement/ssp/library/SPS_Alpha_2012_Mankins.pdf|access-date=24 April 2014|archive-date=23 May 2013|archive-url=https://web.archive.org/web/20130523075630/http://www.nss.org/settlement/ssp/library/SPS_Alpha_2012_Mankins.pdf|url-status=dead}}</ref><ref>{{cite web | url=http://www.nss.org/settlement/ssp/library/1989-SecondBeamedSpacePowerWorkshop.pdf | title=Second Beamed Space-Power Workshop | publisher=Nasa | year=1989 | pages=near page 290 | access-date=2011-11-08 | archive-date=2012-04-02 | archive-url=https://web.archive.org/web/20120402184139/http://www.nss.org/settlement/ssp/library/1989-SecondBeamedSpacePowerWorkshop.pdf | url-status=dead }}</ref><ref>{{cite web | url=http://spirit.as.utexas.edu/~fiso/telecon/Brandhorst_10-27-10/Brandhorst_10-27-10.pdf | title=Options for Lunar Power Beaming | publisher=FISO group | work=Brandhorst | date=October 27, 2010 | author=Henry W. Brandhorst, Jr. | access-date=January 5, 2012 | archive-date=December 9, 2013 | archive-url=https://web.archive.org/web/20131209010800/http://spirit.as.utexas.edu/~fiso/telecon/Brandhorst_10-27-10/Brandhorst_10-27-10.pdf | url-status=dead }}</ref>
== Dealing with launch costs ==
One problem for the SBSP concept is the cost of space launches and the amount of material that would need to be launched.


== Launch costs ==
]s are predicted to provide lower launch costs to low Earth orbit (LEO).<ref>Dr. Lee Valentine in conversation on ''The Space Show'' aired on the 6th of October 2010 said there is a potential for a hundred times cost reduction in the cost of Earth to orbit transportation by using reusable vehicles. </ref><ref>http://www.reactionengines.co.uk/downloads/ssp_skylon_ver2.pdf</ref>


One problem with the SBSP concept is the cost of space launches and the amount of material that would need to be launched.
Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at an acceptable cost. Examples include ]s or ].


Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at an acceptable cost. Examples include ]s or ]. Infrastructure including solar panels, power converters, and power transmitters will have to be built in order to begin the process. This will be extremely expensive and maintaining them will cost even more.
Power beaming from ] by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1-km diameter transmitting antenna, and a 10&nbsp;km diameter receiving rectenna, for a microwave beam at 2.45&nbsp;GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased ] and even potential beam blockage by rain or water droplets. Because of the ], it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.


To give an idea of the scale of the problem, assuming a solar panel mass of 20&nbsp;kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 ], all of which would, in current circumstances, be launched from the Earth. Very lightweight designs could likely achieve 1&nbsp;kg/kW,<ref>{{cite web| url=http://www.you.com.au/news/2005.htm| title= Case For Space Based Solar Power Development| month=August| year=2003| accessdate=2006-03-14}}</ref> meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. This would be the equivalent of between 40 and 150 ] (HLLV) launches to send the material to low earth orbit, where it would likely be converted into subassembly solar arrays, which then could use high-efficiency ion-engine style rockets to (slowly) reach GEO (]). With an estimated serial launch cost for shuttle-based HLLVs of $500 million to $800 million, and launch costs for alternative HLLVs at $78 million, total launch costs would range between $11 billion (low cost HLLV, low weight panels) and $320 billion ('expensive' HLLV, heavier panels). {{Citation needed|date=May 2010}} For comparison, the direct cost of a new coal or nuclear power plant ranges from $3 billion to $6 billion dollars per GW (not including the full cost to the environment from CO2 emissions or storage of spent nuclear fuel, respectively); another example is the ] to the Moon cost a grand total of $24 billion (1970's dollars), taking inflation into account, would cost $140 billion today, more expensive than the construction of the ]. To give an idea of the scale of the problem, assuming a solar panel mass of 20&nbsp;kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 ],<ref>{{cite web|url=https://energy.gov/articles/space-based-solar-power|title=Space-Based Solar Power|work=energy.gov}}</ref> all of which would, in current circumstances, be launched from the Earth. This is, however, far from the state of the art for flown spacecraft, which as of 2015 was 150&nbsp;W/kg (6.7&nbsp;kg/kW), and improving rapidly.<ref>{{cite web|url=https://www.lpi.usra.edu/opag/meetings/aug2015/presentations/day-2/11_beauchamp.pdf|title=Solar Power and Energy Storage for Planetary Missions|date=August 25, 2015}}</ref> Very lightweight designs could likely achieve 1&nbsp;kg/kW,<ref>{{cite web| url=http://www.you.com.au/news/2005.htm| title= Case For Space Based Solar Power Development|date=August 2003| access-date=2006-03-14}}</ref> meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. Beyond the mass of the panels, overhead (including boosting to the desired orbit and stationkeeping) must be added.


{| class="wikitable"
=== Non-conventional launch methods ===
|+ Launch costs for 4 GW to LEO
{{Main|Non-rocket spacelaunch}}
!
! 1&nbsp;kg/kW
! 5&nbsp;kg/kW
! 20&nbsp;kg/kW
|-
! scope=row | $1/kg (Minimum cost at ~$0.13/kWh power, 100% efficiency)
| $4M || $20M || $80M
|-
! scope=row | $2000/kg (ex: ])
| $8B || $40B || $160B
|-
! scope=row | $10000/kg (ex: ])
| $40B || $200B || $800B
|}


To these costs must be added the environmental impact of heavy space launch missions, if such costs are to be used in comparison to earth-based energy production. For comparison, the direct cost of a new coal<ref>{{cite web|url=http://www.netl.doe.gov/technologies/coalpower/cctc/ccpi/pubs/2006_program_update.pdf|archive-url=https://web.archive.org/web/20070110050309/http://www.netl.doe.gov/technologies/coalpower/cctc/ccpi/pubs/2006_program_update.pdf|url-status=dead|archive-date=2007-01-10|title=2006_program_update}}</ref> or nuclear power plant ranges from $3 billion to $6 billion per GW (not including the ] to the environment from {{CO2}} emissions or storage of spent nuclear fuel, respectively).
SBSP costs might be reduced if a means of putting the materials into orbit were developed that did not rely on rockets. Some possible technologies include ground launch systems such as ]s or ]s, which would launch using electrical power, or the geosynchronous orbit ]. However, these require technology that is yet to be developed. ] of Quicklaunch is working on commercialising the 'Hydrogen Gun', a new form of mass driver which proposes to deliver unmanned payloads to orbit for around 5% of regular launch costs (i.e. $500/lb or US$1,000/kg) and perform 5 launches per day.<ref></ref>


== Building from space == == Building from space ==
=== From lunar materials launched in orbit ===
], noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the ].<ref>], "The High Frontier, Human Colonies in Space", ISBN 0-688-03133-1, P.57</ref> ] from the Moon are potentially much lower than from Earth, due to the lower ]. This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial up front capital investment to establish ]s on the Moon.<ref>http://www.youtube.com/watch?v=EgrdAUFFMrA</ref>


=== From lunar materials launched in orbit ===
Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty Solar Power Satellites of 10GW capacity each.<ref>{{cite book| url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19830077470_1983077470.pdf|format=PDF| title=Lunar Resources Utilization for Space Construction| year=1979| author=General Dynamics Convair Division| id=GDC-ASP79-001}}</ref>


], noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the ].<ref>], "The High Frontier, Human Colonies in Space", {{ISBN|0-688-03133-1}}, P.57</ref> ] from the Moon are potentially much lower than from Earth because of the lower ] and lack of ]. This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial upfront capital investment to establish ]s on the Moon.<ref>{{cite web|url=https://www.youtube.com/watch?v=EgrdAUFFMrA |archive-url=https://ghostarchive.org/varchive/youtube/20211219/EgrdAUFFMrA |archive-date=2021-12-19 |url-status=live|title=Colonizing Space - '70s Style!|date=11 December 2009|via=YouTube}}{{cbignore}}</ref> Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty solar power satellites of 10&nbsp;GW capacity each.<ref>{{cite book| url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19830077470_1983077470.pdf| title=Lunar Resources Utilization for Space Construction| year=1979| author=General Dynamics Convair Division| id=GDC-ASP79-001}}</ref>
In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al. published another route to manufacturing using lunar materials with much lower startup costs.<ref>]; Driggers, G.; and ]: New Routes to Manufacturing in Space. Astronautics and Aeronautics, vol. 18, October 1980, pp. 46-51.Several scenarios for the buildup of industry in space are described. One scenario involves a manufacturing facility, manned by a crew of three, entirely on the lunar surface. Another scenario involves a fully automated manufacturing facility, remotely supervised from the earth, with provision for occasional visits by repair crews. A third case involves a manned facility on the Moon for operating a mass-driver launcher to transport lunar materials to a collection point in space and for replicating mass-drivers.</ref> This 1980s SPS concept relied less on human presence in space and more on partially ] on the lunar surface under ] of workers stationed on Earth. The high ] of this proposal derives from the Moon's much shallower ].


In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al. published another route to manufacturing using lunar materials with much lower startup costs.<ref>{{cite journal | last1 = O'Neill | first1 = Gerard K. | author-link = Gerard K. O'Neill | author-link3 = Brian O'Leary | last2 = Driggers | first2 = G. | last3 = O'Leary | first3 = B. | year = 1980 | title = New Routes to Manufacturing in Space | journal = Astronautics and Aeronautics | volume = 18 | pages = 46–51 | bibcode = 1980AsAer..18...46G }} Several scenarios for the buildup of industry in space are described. One scenario involves a manufacturing facility, with a crew of three, entirely on the lunar surface. Another scenario involves a fully automated manufacturing facility, remotely supervised from the earth, with provision for occasional visits by repair crews. A third case involves a crewed facility on the Moon for operating a mass-driver launcher to transport lunar materials to a collection point in space and for replicating mass-drivers.</ref> This 1980s SPS concept relied less on human presence in space and more on partially ] on the lunar surface under ] of workers stationed on Earth. The high ] of this proposal derives from the Moon's much shallower ].
Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in O'Neill's vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites.


Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the ], first described by Jerome Pearson.<ref>Pearson, Jerome; Eugene Levin, John Oldson and Harry Wykes (2005). Lunar Space Elevators for Cislunar Space Development Phase I Final Technical Report (PDF).</ref> It would require establishing ] mining and solar cell manufacturing facilities on the ].{{Citation needed|date=October 2010}} Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in O'Neill's vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites. Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the ], first described by Jerome Pearson.<ref>Pearson, Jerome; Eugene Levin, John Oldson and Harry Wykes (2005). Lunar Space Elevators for Cislunar Space Development Phase I Final Technical Report (PDF).</ref> It would require establishing ] mining and solar cell manufacturing facilities on the ].{{Citation needed|date=October 2010}}


=== On the Moon === === On the Moon ===

] suggests the Moon is the optimum location for solar power stations, and promotes '''lunar solar power'''.<ref></ref><ref></ref> The main advantage he envisions is construction largely from locally available lunar materials, using ], with a ] mobile factory, a crane to assemble the microwave reflectors, and rovers to assemble solar cells, which would significantly reduce launch costs compared to SBSP designs. Power relay satellites orbiting around earth and the Moon reflecting the microwave beam are also part of the project.<ref>http://www.moonbase-italia.org/PAPERS/D1S2-MB%20Assessment/D2S2-06EnergySupport/D2S2-06EnergySupport.Criswell.pdf</ref> Another design combined the rovers with the factory and directly paves the Moon with a thin film of solar cells.<ref>http://www.cam.uh.edu/SpaRC/ISRU%202p%20v1%20022007.pdf</ref> The ] proposed using combination of lasers and microwave for the lunar ring concept, along with power relay satellites.<ref>http://lunarscience.arc.nasa.gov/articles/the-luna-ring-concept</ref><ref>http://ssi.org/ssi-conference-abstracts/space-manufacturing-8/</ref>
Physicist Dr ] suggests the Moon is the optimum location for solar power stations, and promotes lunar-based solar power.<ref>{{cite web|url=http://www.uh.edu/news-events/tip-sheets/spaceexploration-tips.php|title=UH Mobile - Space-Related Centers at UH Target Next 50 Years of Exploration}}</ref><ref>{{cite web|url=http://www.isso.uh.edu/criswell/papers.html |title=Criswell - Publications and Abstracts|url-status=dead|archive-url=https://web.archive.org/web/20100622063857/http://www.isso.uh.edu/criswell/papers.html|archive-date=2010-06-22}}</ref><ref>{{cite magazine |url=https://www.wired.co.uk/article/moon-solar-energy-power |title=Beaming solar energy from the Moon could solve Earth's energy crisis |author=David Warmflash |date=29 March 2017 |magazine=Wired UK |publisher=Condé Nast |access-date=February 27, 2018 }}</ref> The main advantage he envisions is construction largely from locally available lunar materials, using ], with a ] mobile factory and crane to assemble the microwave reflectors, and rovers to assemble and pave solar cells,<ref>{{cite web |url=http://www.cam.uh.edu/SpaRC/ISRU%202p%20v1%20022007.pdf |title=Lunar Solar Cell Manufacturing |website=www.cam.uh.edu |access-date=12 January 2022 |archive-url=https://web.archive.org/web/20100622143653/http://www.cam.uh.edu/SpaRC/ISRU%202p%20v1%20022007.pdf |archive-date=22 June 2010 |url-status=dead}}</ref> which would significantly reduce launch costs compared to SBSP designs. Power relay satellites orbiting around earth and the Moon reflecting the microwave beam are also part of the project. A demo project of 1 GW starts at $50 billion.<ref>{{cite conference |author=DAVID R. CRISWEL |url=http://www.moonbase-italia.org/PAPERS/D1S2-MB%20Assessment/D2S2-06EnergySupport/D2S2-06EnergySupport.Criswell.pdf |title=LUNAR SOLAR POWER SYSTEM: INDUSTRIAL RESEARCH, DEVELOPMENT, AND DEMONSTRATION |publisher=World Energy Council |conference=18th Congress, Buenos Aires, October 2001 |via=www.moonbase-italia.org |access-date=12 January 2022 |archive-url=https://web.archive.org/web/20120326081335/http://www.moonbase-italia.org/PAPERS/D1S2-MB%20Assessment/D2S2-06EnergySupport/D2S2-06EnergySupport.Criswell.pdf |archive-date=26 March 2012 |url-status=dead}}</ref> The ] use combination of lasers and microwave for the ] concept, along with power relay satellites.<ref>{{Cite web|url=https://sservi.nasa.gov/articles/the-luna-ring-concept/|title=The Luna Ring concept|website=Solar System Exploration Research Virtual Institute}}</ref><ref>{{cite web | url=http://justsap.org/wp-content/uploads/28_Shigeru-Aoki_Luna_Ring.pdf | title=Lunar Solar Power Generation, "The LUNA RING", Concept and Technology | publisher=Japan-U.S. Science, Technology & Space Applications Program | year=2009 | url-status=dead | archive-url=https://web.archive.org/web/20131208175506/http://justsap.org/wp-content/uploads/28_Shigeru-Aoki_Luna_Ring.pdf | archive-date=2013-12-08 }}</ref>


=== From an asteroid === === From an asteroid ===
] has also been seriously considered. A NASA design study<ref>Space Resources, NASA SP-509, Vol 1.</ref> evaluated a 10,000 ton mining vehicle (to be assembled in orbit) that would return a 500,000 ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition.<ref>http://settlement.arc.nasa.gov/spaceres/IV-2.html</ref>


] has also been seriously considered. A NASA design study<ref>Space Resources, NASA SP-509, Vol 1.</ref> evaluated a 10,000-ton mining vehicle (to be assembled in orbit) that would return a 500,000-ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition.<ref>{{cite web |url=http://settlement.arc.nasa.gov/spaceres/IV-2.html |archive-date=2010-05-31|archive-url=https://web.archive.org/web/20100531192813/http://settlement.arc.nasa.gov/spaceres/IV-2.html|url-status=dead |title=Retrieval of Asteroidal Materials}}</ref> One proposal is to capture the asteroid ] into Earth orbit and convert it into 150 solar power satellites of 5 GW each or the larger asteroid 1999 AN10, which is 50 times the size of Apophis and large enough to build 7,500 5-gigawatt solar power satellites<ref>{{cite web |title=Technologies for Asteroid Capture into Earth Orbit |date=May 2011 |author=Stephen D. Covey |url=http://www.nss.org/settlement/asteroids/capture.html |access-date=2012-01-29 |archive-date=2011-12-12 |archive-url=https://web.archive.org/web/20111212205647/http://www.nss.org/settlement/asteroids/capture.html |url-status=dead}}</ref>
=== Gallery ===
<gallery>
Image:Lunar base concept drawing s78 23252.jpg|A Lunar base with a mass driver (the long structure that goes toward the horizon). NASA conceptual illustration
Image:Advanced Automation for Space Missions figure 5-19.jpg|An artist's conception of a "self-growing" robotic lunar factory.
File:Lunar solar power.jpg|Microwave reflectors on the moon and teleoperated robotic paving rover and crane.
File:Lunar solar crawler 2.png| “Crawler” traverses Lunar surface, smoothing, melting a top layer of regolith, then depositing elements of silicon PV cells directly on surface
File:Lunar solar crowler.png| Sketch of the Lunar Crawler to be used for fabrication of lunar solar cells on the surface of the Moon.
File:Autonomous solar-powered lunar photovoltaic cell production rover.png|Autonomous solar-powered lunar photovoltaic cell production rover
File:Solar.GIF|Shown here is an array of solar collectors that convert power into microwave beams directed toward Earth.
File:Solar power satellite from an asteroid.jpg|A solar power satellite built from a mined asteroid.
</gallery>


==Counter arguments== == Safety ==
=== Safety ===


The potential exposure of humans and animals on the ground to the high power microwave beams is a significant concern with these systems. At the Earth's surface, a suggested SPSP microwave beam would have a maximum intensity at its center, of 23&nbsp;mW/cm<sup>2</sup>.<ref name="intensity">{{cite journal| first= G.M.. .| last= Hanley. | title= Satellite Concept Power Systems (SPS) Definition Study | journal= NASA CR 3317, Sept 1980 | url= https://ntrs.nasa.gov/api/citations/19800022396/downloads/19800022396.pdf }}</ref> While this is less than 1/4 the ], microwaves penetrate much deeper into tissue than sunlight, and at this level would exceed the current United States ] (OSHA) workplace exposure limits for microwaves at 10&nbsp;mW/cm<sup>2</sup><ref> interpretation of General Industry (29 CFR 1910) 1910 Subpart G, Occupational Health and Environmental Control 1910.97, Non-ionizing radiation.</ref> At 23&nbsp;mW/cm<sup>2</sup>, studies show humans experience significant deficits in spatial learning and memory.<ref name="Zhi Wang Hu 2017 p. ">{{cite journal | last1=Zhi | first1=Wei-Jia | last2=Wang | first2=Li-Feng | last3=Hu | first3=Xiang-Jun | title=Recent advances in the effects of microwave radiation on brains | journal=Military Medical Research | volume=4 | issue=1 | date=2017 | issn=2054-9369 | pmid=29502514 | pmc=5607572 | doi=10.1186/s40779-017-0139-0 | doi-access=free | page=29}}</ref> If the diameter of the proposed SPSP array is increased by 2.5x, the energy density on the ground increases to 1&nbsp;W/cm<sup>2</sup>.{{efn| 1=An increase in space array diameter of 2.5x increases the array element count by 6.25x, which increases total power transmitted by this factor. In addition for a coherent microwave beam, the ground spot area decreases by 6.25x, therefore the power density on ground increases by 6.25<sup>2</sup> = 40x. This increases the proposed 23&nbsp;W/cm<sup>2</sup> to about 1&nbsp;W/cm<sup>2</sup>}} At this level, the ] for mice is 30-60 seconds of microwave exposure.<ref name="apps.dtic.mil f957">{{cite web | title=Defense Technical Information Center | website=apps.dtic.mil | url=https://apps.dtic.mil/sti/citations/AD0774823 | access-date=31 March 2024}}</ref> While designing an array with 2.5x larger diameter should be avoided, the ] military potential of such a system is readily apparent.
The use of ] has been the most controversial issue in considering any SPS design.


With good array sidelobe design, outside the receiver may be less than the OSHA long-term levels <ref>2081 A Hopeful View of the Human Future, by ], {{ISBN|0-671-24257-1}}, P. 182-183</ref> as over 95% of the beam energy will fall on the rectenna. However, any accidental or intentional mis-pointing of the satellite could be deadly to life on Earth within the beam.
At the Earth's surface, a suggested microwave beam would have a maximum intensity at its center, of 23&nbsp;mW/cm<sup>2</sup> (less than 1/4 the ]), and an intensity of less than 1&nbsp;mW/cm<sup>2</sup> outside of the rectenna fenceline (the receiver's perimeter).<ref name="intensity">{{cite journal| first= G.M.. .| last= Hanley. | title= Satellite Concept Power Systems (SPS) Definition Study
| journal= NASA CR 3317, Sept 1980 | url= http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800022396_1980022396.pdf|format=PDF}}
</ref> These compare with current United States ] (OSHA) workplace exposure limits for microwaves, which are 10&nbsp;mW/cm<sup>2</sup>,<ref> interpretation of General Industry (29 CFR 1910) 1910 Subpart G, Occupational Health and Environmental Control 1910.97, Non-ionizing radiation.</ref> - the limit itself being expressed in voluntary terms and ruled unenforceable for Federal OSHA enforcement purposes.{{Citation needed|date=October 2009}} A beam of this intensity is therefore at its center, of a similar magnitude to current safe workplace levels, even for long term or indefinite exposure. Outside the receiver, it is far less than the OSHA long-term levels<ref>2081 A Hopeful View of the Human Future, by ], ISBN 0-671-24257-1, P. 182-183</ref> Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world.<ref>IEEE, 01149129.pdf</ref> It is important for system efficiency that as much of the microwave radiation as possible be focused on the rectenna. Outside of the rectenna, microwave intensities rapidly decrease, so nearby towns or other human activity should be completely unaffected.<ref name="IEEE 602864"/>


Exposure to the beam is able to be minimized in other ways. On the ground, physical access is controllable (e.g., via fencing), and typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a ]), which will intercept the microwaves. Other aircraft (]s, ], etc.) can avoid exposure by observing airflight control spaces, as is currently done for military and other controlled airspace. Exposure to the beam can be minimized in various ways. On the ground, assuming the beam is pointed correctly, physical access must be controllable (e.g., via fencing). Typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a ]), which will intercept the microwaves.{{Original research inline|date=March 2017}} Other aircraft (]s, ], etc.) can avoid exposure by using controlled airspace, as is currently done for military and other controlled airspace. In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Suggestions have been made to locate rectennas offshore,<ref>{{cite journal |title=Solar power satellite offshore rectenna study |journal=Final Report Rice Univ |year=1980 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810004047.pdf |bibcode=1980ruht.reptT..... }}</ref><ref>{{cite journal |hdl=2060/19820014867 |first=J. W. | last=Freeman | display-authors=etal | title=Offshore rectenna feasibility | journal=In NASA, Washington the Final Proc. of the Solar Power Satellite Program Rev. P 348-351 (SEE N82-22676 13-44) |pages=348 | bibcode=1980spsp.nasa..348F| year=1980 }}</ref> but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.


A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective ] antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. If the phase offset to the pilot is chosen the same for all elements, the transmitted beam should be centered precisely on the rectenna and have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused.<ref name="IEEE 602864">{{cite book |doi=10.1109/MWSYM.1997.602864 |chapter=Automatic beam steered active antenna receiver |title=1997 IEEE MTT-S International Microwave Symposium Digest |volume=2 |pages=599–602 |year=1997 |last1=Gupta |first1=S. |last2=Fusco |first2=V.F. |isbn=978-0-7803-3814-2 |s2cid=21796252 }}</ref> Such a system would not focus its power beam very effectively anywhere that did not have a pilot beam transmitter. The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied.
The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe levels, even in principle.


== Timeline ==
In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations.<ref></ref>


=== In the 20th century ===
Some have suggested locating rectennas offshore,<ref>"Solar power satellite offshore rectenna study", Final Report Rice Univ., Houston, TX., 11/1980, Abstract: http://adsabs.harvard.edu/abs/1980ruht.reptT.....</ref><ref>{{cite journal|first= J. W.; .| last=Freeman, et al. | title=Offshore rectenna feasbility | journal=In NASA, Washington the Final Proc. of the Solar Power Satellite Program Rev. p 348-351 (SEE N82-22676 13-44) | bibcode=1980spsp.nasa..348F}}</ref> but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.

A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective ] antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused.<ref name="IEEE 602864">IEEE Article No: 602864, Automatic Beam Steered Antenna Receiver&nbsp;— Microwave</ref> Such a system would be physically incapable of focusing its power beam anywhere that did not have a pilot beam transmitter.

The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied, but nothing has been suggested which might lead to any significant effect.

=== Atmospheric damage due to launches ===

When hot rocket exhaust reacts with atmospheric ], it can form nitrogen compounds.{{Citation needed|date=October 2010}} These nitrogen compounds are problematic when they form in the stratosphere, as they can damage the ozone layer. However, the environmental effect of rocket launches is negligible compared to higher volume polluters, such as airplanes and automobiles.{{Citation needed|date=August 2011}}

== Timeline ==
*'''1968''': Dr. ] introduces the concept of a "solar power satellite" system with square miles of solar collectors in high ] for collection and conversion of sun's energy into a ] beam to transmit usable energy to large receiving antennas (]s) on Earth for distribution.


* 1941: Isaac Asimov published the science fiction short story "Reason," in which a space station transmits energy collected from the sun to various planets using microwave beams. "Reason" was published in the "Astounding Science Fiction" magazine. <ref>{{Cite web |title=Reason |url=https://www.goodreads.com/book/show/18216196-reason |access-date=2024-02-29 |website=Goodreads |language=en}}</ref>
*'''1973''': Dr. Peter Glaser is granted ] number 3,781,647 for his method of transmitting power over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.<ref name="Glaser">{{cite journal|first=Peter E.| last=Glaser| title=Method And Apparatus For Converting Solar Radiation To Electrical Power | journal=United States Patent 3,781,647 |date=December 25, 1973 |
*1968: ] introduces the concept of a "solar power satellite" system with square miles of solar collectors in high ] for collection and conversion of sun's energy into a ] beam to transmit usable energy to large receiving antennas (]s) on Earth for distribution.
* 1973: Peter Glaser is granted ] number 3,781,647 for his method of transmitting power over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.<ref name="Glaser">{{cite journal|first=Peter E.| last=Glaser| title=Method And Apparatus For Converting Solar Radiation To Electrical Power | journal=United States Patent 3,781,647 |date=December 25, 1973 |
url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=3,781,647.PN.&OS=PN/3,781,647&RS=PN/3,781,647}}</ref> url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=3,781,647.PN.&OS=PN/3,781,647&RS=PN/3,781,647}}</ref>
* 1978–1981: The ] and ] examine the solar power satellite (SPS) concept extensively, publishing design and feasibility studies.
* 1987: ] a Canadian experiment
* 1995–1997: NASA conducts a "Fresh Look" study of space solar power (SSP) concepts and technologies.
* 1998: The Space Solar Power Concept Definition Study (CDS) identifies credible, commercially viable SSP concepts, while pointing out technical and programmatic risks.
* 1998: Japan's space agency begins developing a space solar power system (SSPS), a program that continues to the present day.<ref>{{cite web|title=Introduction of Research: About the SSPS|url=https://www.kenkai.jaxa.jp/eng/research/ssps/ssps-ssps.html|publisher=JAXA | access-date=25 November 2022}}</ref>
* 1999: NASA's ] ('']'') begins.
* 2000: John Mankins of NASA testifies in the ], saying "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities. A technology roadmap has been developed that lays out potential paths for achieving all needed advances&nbsp;— albeit over several decades.<ref name="Mankins" />


=== In the 21st century ===
*'''1978-81''': The ] and ] examine the solar power satellite (SPS) concept extensively, publishing design and feasibility studies.
*'''1982''': ] proposal <ref>http://www.boeing.com/history/boeing/solarsat.html</ref>
*'''1987''': ] a canadian experiment
*'''1994''': The ] conducts the ] using a satellite launched into low Earth orbit by a ].
*'''1995–97''': NASA conducts a “Fresh Look” study of space solar power (SSP) concepts and technologies.
*'''1998''': The Space Solar Power Concept Definition Study (CDS) identifies credible, commercially viable SSP concepts, while pointing out technical and programmatic risks.
*'''1998''': Japan's space agency begins developing a Space Solar Power System (SSPS), a program that continues to the present day.
*'''1999''': NASA's ] ('']'') begins.


* 2001: ] (One of Japan's national space agencies before it became part of ]) announces plans to perform additional research and prototyping by launching an experimental satellite with 10 kilowatts and 1 megawatt of power.<ref>{{cite web|url=http://www.space.com/businesstechnology/technology/nasda_solar_sats_011029.html|title=Controversy Flares Over Space-Based Solar Power Plans|website=]|date=2 December 2009}}</ref><ref>Presentation of relevant technical background with diagrams: http://www.spacefuture.com/archive/conceptual_study_of_a_solar_power_satellite_sps_2000.shtml</ref>
*'''2000''': John Mankins of NASA testifies in the ], saying "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities. A technology roadmap has been developed that lays out potential paths for achieving all needed advances&nbsp;— albeit over several decades.<ref name="Mankins" />
* 2003: ] studies<ref>{{cite web|url= http://www.esa.int/gsp/ACT/nrg/op/SPS/History.htm|title= History of research on SPS|url-status= dead|archive-url= https://web.archive.org/web/20121022004245/http://www.esa.int/gsp/ACT/nrg/op/SPS/History.htm|archive-date= 2012-10-22}}</ref>
* 2007: The ]'s ] (NSSO) issues a report<ref>{{Cite web |url=http://www.nss.org/settlement/ssp/library/final-sbsp-interim-assessment-release-01.pdf |title=National Security Space Office Interim Assessment Phase 0 Architecture Feasibility Study, October 10, 2007 |access-date=October 20, 2007 |archive-date=October 25, 2007 |archive-url=https://web.archive.org/web/20071025092316/http://www.nss.org/settlement/ssp/library/final-sbsp-interim-assessment-release-01.pdf |url-status=dead }}</ref> on October 10, 2007 stating they intend to collect solar energy from space for use on Earth to help the United States' ongoing relationship with the ] and the battle for oil. A demo plant could cost $10 billion, produce 10 megawatts, and become operational in 10 years.<ref>{{cite web |title= Making the case, again, for space-based solar power|url= http://www.thespacereview.com/article/1978/1 |publisher= thespacereview.com |date= November 28, 2011}}</ref>
* 2007: In May 2007, a workshop is held at the US ] to review the current state of the SBSP market and technology.<ref> Date: May 14–16, 2007; Location: MIT, Cambridge MA</ref>
* 2010: Professors Andrea Massa and Giorgio Franceschetti announce a special session on the "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" at the 2010 ] International Symposium on Antennas and Propagation.<ref>{{citation | url=http://www.apsursi2010.org/?m=page&id=47 | title=Special Session list | publisher=IEEE International Symposium on Antennas and Propagation | date=April 20, 2010}}</ref>
* 2010: The Indian Space Research Organisation and US' National Space Society launched a joint forum to enhance partnership in harnessing solar energy through space-based solar collectors. Called the Kalam-NSS Initiative after the former Indian President ], the forum will lay the groundwork for the space-based solar power program which could see other countries joining in as well.<ref>{{citation | url=http://ecopolitology.org/2010/11/10/us-india-launch-space-based-solar-energy-initiative/ | title=US, India launch space based solar energy initiative | author=Mridul Chadha | date=November 10, 2010 | url-status=dead | archive-url=https://web.archive.org/web/20120731010405/http://ecopolitology.org/2010/11/10/us-india-launch-space-based-solar-energy-initiative/ | archive-date=July 31, 2012 }}</ref>
* 2010: ''Sky's No Limit: Space-Based solar power, the next major step in the Indo-US strategic partnership?'' written by USAF Lt Col Peter Garretson was published at the Institute for Defence Studies and Analysis.<ref>{{Cite web|url=http://www.idsa.in/occasionalpapers/SkysNoLimit_pgarretson_2010|title=Sky's No Limit: Space-based solar power, the next major step in the Indo-US strategic partnership? {{!}} Institute for Defence Studies and Analyses|website=www.idsa.in|access-date=2016-05-21}}</ref>
*2012: China proposed joint development between India and China towards developing a solar power satellite, during a visit by former Indian President ].<ref>{{citation | url=https://timesofindia.indiatimes.com/india/China-proposes-space-collaboration-with-India/articleshow/17066537.cms | archive-url=https://web.archive.org/web/20130523152006/http://articles.timesofindia.indiatimes.com/2012-11-02/india/34877401_1_space-solar-power-space-collaboration-v-ponraj | url-status=live | archive-date=May 23, 2013 | title=US, China proposes space collaboration with India | author=PTI | work=] | date= November 2, 2012 }}</ref>
*2015: The is established between Caltech and Northrop Grumman Corporation. An estimated $17.5 million is to be provided over a three-year project for development of a space-based solar power system.
*2015: JAXA announced on 12 March 2015 that they wirelessly beamed 1.8 kilowatts 50 meters to a small receiver by converting electricity to microwaves and then back to electricity.<ref name="ATarantola" /><ref name="PKT" />
* 2016: Lt Gen. Zhang Yulin, deputy chief of the armament development department of the Central Military Commission, suggested that China would next begin to exploit Earth-Moon space for industrial development. The goal would be the construction of space-based solar power satellites that would beam energy back to Earth.<ref>{{Cite web|title=Exploiting earth-moon space: China's ambition after space station|url=http://news.xinhuanet.com/english/2016-03/07/c_135164574.htm|archive-url=https://web.archive.org/web/20160308013331/http://news.xinhuanet.com/english/2016-03/07/c_135164574.htm|url-status=dead|archive-date=March 8, 2016|access-date=2016-05-21|website=]}}</ref>
* 2016: A with membership from the Naval Research Laboratory (NRL), Defense Advanced Projects Agency (DARPA), Air Force Air University, Joint Staff Logistics (J-4), Department of State, Makins Aerospace and Northrop Grumman won the Secretary of Defense (SECDEF) / Secretary of State (SECSTATE) / USAID Director's agency-wide D3 (Diplomacy, Development, Defense) Innovation Challenge with a that the US must lead in space solar power. The proposal was followed by a
* 2016: has transformed the D3 proposal into active petitions on the White House Website "America Must Lead the Transition to Space-Based Energy"and Change.org "USA Must Lead the Transition to Space-Based Energy" along with the following .
* 2016: Erik Larson and others from NOAA produce a paper "Global atmospheric response to emissions from a proposed reusable space launch system"<ref>{{cite journal |doi=10.1002/2016EF000399 |title=Global atmospheric response to emissions from a proposed reusable space launch system |journal=Earth's Future |volume=5 |issue=1 |pages=37–48 |year=2017 |last1=Larson |first1=Erik J. L. |last2=Portmann |first2=Robert W. |last3=Rosenlof |first3=Karen H. |last4=Fahey |first4=David W. |last5=Daniel |first5=John S. |last6=Ross |first6=Martin N. |bibcode=2017EaFut...5...37L |url=https://zenodo.org/record/1000659 |doi-access=free }}</ref> The paper makes a case that up to 2 TW/year of power satellites could be constructed without intolerable damage to the atmosphere. Before this paper, there was concern that the {{NOx}} produced by reentry would destroy too much ozone.
* 2016: proposes CASSIOPeiA (Constant Aperture, Solid State, Integrated, Orbital Phased Array) a new concept SPS
*2017: NASA selects focused on investments in space. The Colorado School of Mines focuses on "21st Century Trends in Space-Based Solar Power Generation and Storage."
*2019: Aditya Baraskar and Prof Toshiya Hanada from proposed Energy Orbit (E-Orbit),<ref name="E-Orbit">{{cite web|work=6th Space Solar Power (SSPS) Symposium (Online)|date= 4 December 2020|title= Energy Orbit |url=https://www.sspss.jp/%e3%82%b7%e3%83%b3%e3%83%9d%e3%82%b8%e3%82%a6%e3%83%a0/2020%e5%b9%b4/}}</ref> a small Space Solar Power Satellite constellation for power beaming between satellites in low earth orbit. A total of 1600 satellites to transmit 10 kilowatts of electricity in a 500&nbsp;km radius at an altitude of 900&nbsp;km.<ref name="APRSAF26">{{cite web|work=The 26th Session of the Asia-Pacific Regional Space Agency Forum (APRSAF-26)|date= 26 November 2019|title= Satellite to Satellite Wireless Power Transmission System for small Space Solar Power Station |url=https://www.aprsaf.org/annual_meetings/aprsaf26/working_groups_stwg.php}}</ref>
*2019: China creates a test base for SBSP, and announces plan to launch a working megawatt-grade 200-tonne SBSP station by 2035.
*2020: US Naval Research Laboratory launches test satellite.<ref name="usnavy2020">{{cite press release|publisher=U.S. Naval Research Laboratory Public Affairs|date=May 18, 2020|title=Naval Research Laboratory Conducts First Test of Solar Power Satellite Hardware in Orbit |url=https://www.navy.mil/submit/display.asp?story_id=112989|archive-url=https://web.archive.org/web/20200519022252/https://www.navy.mil/submit/display.asp?story_id=112989 |archive-date=May 19, 2020|access-date=19 May 2020|url-status=dead|website=www.navy.mil}}</ref> Also the USAF has its ] (SSPIDR) planning to launch the ARACHNE test satellite.<ref>{{Cite web |title=Space Power Beaming |website=Air Force Research Laboratory |url=https://afresearchlab.com/technology/successstories/space-power-beaming/ |access-date=2021-04-28 |url-status=dead |archive-date=2021-04-28 |archive-url=https://web.archive.org/web/20210428183529/https://afresearchlab.com/technology/successstories/space-power-beaming/}}</ref> Arachne is due to launch in 2024.<ref>{{Cite web|first=Leonard|last=David|date=April 8, 2021 |url=https://www.space.com/x-37b-space-plane-solar-power-beaming|title=Space-based solar power getting key test aboard US military's mysterious X-37B space plane|website=Space.com}}</ref>
*2021: ] announces that it planned to launch a SBSP test array by 2023.
*2022: The ] in the ] announced to launch the first power station in space during the mid-2040s, to "provide 30 percent of the UK’s (greatly increased) electricity demand" and "to slash the UK’s dependence on fossil fuels" and foreign ties.<ref>{{cite web|url=https://spaceenergyinitiative.org.uk/uk-to-launch-first-power-station-in-space-limitless-green-energy-to-slash-foreign-ties/|title=UK to launch first power station in SPACE – limitless green energy to slash foreign ties|date=21 March 2022|access-date=18 April 2022|website=Space Energy Initiative}}</ref>
*2022: The ] proposed a program called ] to operate Solar Power Satellites from 2030.<ref>{{Cite web |last=Foust |first=Jeff |date=2022-08-19 |title=ESA to request funding for space-based solar power study |url=https://spacenews.com/esa-to-request-funding-for-space-based-solar-power-study/ |access-date=2023-10-29 |website=SpaceNews |language=en-US}}</ref>
*2023: Caltech's Space Solar Power Demonstrator (SSPD-1) beams "detectable power" to Earth.<ref name=caltech2023edu/>


== Non-typical configurations and architectural considerations ==
*'''2001''': Dr. Neville Marzwell of NASA states, "We now have the technology to convert the sun's energy at the rate of 42 to 56 percent... We have made tremendous progress. ...If you can concentrate the sun's rays through the use of large mirrors or lenses you get more for your money because most of the cost is in the PV arrays... There is a risk element but you can reduce it... You can put these small receivers in the desert or in the mountains away from populated areas. ...We believe that in 15 to 25 years we can lower that cost to 7 to 10 cents per kilowatt hour. ...We offer an advantage. You don't need cables, pipes, gas or copper wires. We can send it to you like a cell phone call—where you want it and when you want it, in real time."<ref> Mar, 2001 ''from ''</ref>


The typical reference system-of-systems involves a significant number (several thousand multi-gigawatt systems to service all or a significant portion of Earth's energy requirements) of individual satellites in GEO. The typical reference design for the individual satellite is in the 1-10 GW range and usually involves planar or concentrated solar photovoltaics (PV) as the energy collector / conversion. The most typical transmission designs are in the 1–10&nbsp;GHz (2.45 or 5.8&nbsp;GHz) RF band where there are minimum losses in the atmosphere. Materials for the satellites are sourced from, and manufactured on Earth and expected to be transported to LEO via re-usable rocket launch, and transported between LEO and GEO via chemical or electrical propulsion. In summary, the architecture choices are:
*'''2001''': ] (Japan's national space agency) announces plans to perform additional research and prototyping by launching an experimental satellite with 10 kilowatts and 1 megawatt of power.<ref></ref><ref>Presentation of relevant technical background with diagrams: http://www.spacefuture.com/archive/conceptual_study_of_a_solar_power_satellite_sps_2000.shtml</ref>
* Location = GEO
* Energy Collection = PV
* Satellite = Monolithic Structure
* Transmission = RF
* Materials & Manufacturing = Earth
* Installation = RLVs to LEO, Chemical to GEO
There are several interesting design variants from the reference system:


Alternate energy collection location: While GEO is most typical because of its advantages of nearness to Earth, simplified pointing and tracking, very small time in occultation, and scalability to meet all global demand several times over, other locations have been proposed:
*'''2003''': ] studies<ref>http://www.esa.int/gsp/ACT/nrg/op/SPS/History.htm</ref>
* Sun Earth L1: Robert Kennedy III, Ken Roy & David Fields have proposed a variant of the L1 sunshade called "Dyson Dots"<ref>{{cite journal |doi=10.1016/j.actaastro.2012.10.022 |title=Dyson Dots: Changing the solar constant to a variable with photovoltaic lightsails |journal=Acta Astronautica |volume=82 |issue=2 |pages=225–37 |year=2013 |last1=Kennedy |first1=Robert G. |last2=Roy |first2=Kenneth I. |last3=Fields |first3=David E. |bibcode=2013AcAau..82..225K }}</ref> where a multi-terawatt primary collector would beam energy back to a series of LEO sun-synchronous receiver satellites. The much farther distance to Earth requires a correspondingly larger transmission aperture.
* Lunar surface: ] has proposed using the Lunar surface itself as the collection medium, beaming power to the ground via a series of microwave reflectors in Earth Orbit. The chief advantage of this approach would be the ability to manufacture the solar collectors in-situ without the energy cost and complexity of launch. Disadvantages include the much longer distance, requiring larger transmission systems, the required "overbuild" to deal with the lunar night, and the difficulty of sufficient manufacturing and pointing of reflector satellites.<ref>{{Cite web |url=http://www.lunarsolarpower.org/#!criswell/czxo |title=Lunarsolarpower |access-date=2016-05-23 |archive-date=2016-05-26 |archive-url=https://web.archive.org/web/20160526215248/http://www.lunarsolarpower.org/#!criswell/czxo |url-status=dead}}</ref>
* MEO: MEO systems have been proposed for in-space utilities and beam-power propulsion infrastructures. For example, see Royce Jones' paper.<ref>{{cite web |url=http://www.earthspaceagency.org/images/stories/BeamedEnergyPublish.pdf |author=Royce Jones |title=Beamed Energy In-Space Transportation System for Near Space Colonization |access-date=2016-05-22 |url-status=dead |archive-url=https://web.archive.org/web/20160610012509/http://www.earthspaceagency.org/images/stories/BeamedEnergyPublish.pdf |archive-date=2016-06-10 }}</ref>
* Highly elliptical orbits: Molniya, Tundra, or Quazi Zenith orbits have been proposed as early locations for niche markets, requiring less energy to access and providing good persistence.<ref>http://www.sspi.gatech.edu/welsom_isdc_reed.pdf Kevin Reed's QGSO proposal (Slide 25)</ref>
* Sun-sync LEO: In this near Polar Orbit, the satellites precess at a rate that allows them to always face the Sun as they rotate around Earth. This is an easy to access orbit requiring far less energy, and its proximity to Earth requires smaller (and therefore less massive) transmitting apertures. However disadvantages to this approach include having to constantly shift receiving stations, or storing energy for a burst transmission. This orbit is already crowded and has significant space debris.
* Equatorial LEO: Japan's SPS 2000 proposed an early demonstrator in equatorial LEO in which multiple equatorial participating nations could receive some power.<ref>{{Cite web|url=http://www.spacefuture.com/power/sps2000.shtml |title=Space Future - SPS 2000 - an SPS Demonstrator}}</ref>
* Earth's surface: Narayan Komerath has proposed a space power grid where excess energy from an existing grid or power plant on one side of the planet can be passed up to orbit, across to another satellite and down to receivers.<ref>{{cite web|url=https://smartech.gatech.edu/bitstream/handle/1853/32263/217-422-1-PB.pdf|title=The Space Power Grid: Synergy Between Space, Energy and Security Policies|first=Narayanan |last=Komerath|publisher=Georgia Tech|access-date=December 4, 2022}}</ref>
Energy collection: The most typical designs for solar power satellites include photovoltaics. These may be planar (and usually passively cooled), concentrated (and perhaps actively cooled). However, there are multiple interesting variants.
* Solar thermal: Proponents of solar thermal have proposed using concentrated heating to cause a state change in a fluid to extract energy via rotating machinery followed by cooling in radiators. Advantages of this method might include overall system mass (disputed), eliminating degradation due to solar-wind damage, and radiation tolerance. One recent thermal solar power satellite design by ] and others has been visualized here. A related concept is here: The proposed radiators are thin wall platic tube filled with low pressure (2.4 kPa) and temperature (20 deg C) steam.
* Solar pumped laser: Japan has pursued a ], where sunlight directly excites the lasing medium used to create the coherent beam to Earth.
* Stellaser: A hypothetical concept of a very large laser where a star provides both the lasing energy and the lasing medium, producing a steerable energy beam of unrivaled power.
* Fusion decay: This version of a power-satellite is not "solar". Rather, the vacuum of space is seen as a "feature not a bug" for traditional fusion. Per Paul Werbos, after fusion even neutral particles decay to charged particles which in a sufficiently large volume would allow direct conversion to current.{{Citation needed|date=March 2017}}
* ]: Also called a ]. Here the satellite makes use not of the photons from the Sun but rather the charged particles in the solar wind which via electro-magnetic coupling generate a current in a large loop.
* Direct mirrors: Early concepts for direct mirror re-direction of light to planet Earth suffered from the problem that rays coming from the sun are not parallel but are expanding from a disk and so the size of the spot on the Earth is quite large. Lewis Fraas has explored an array of parabolic mirrors to augment existing solar arrays.<ref>{{cite conference |url=http://www.mtu.edu/ece/department/faculty/full-time/zekavat/SSP2015_fraas.pdf |title=Self Pointing Mirror Satellites for Solar Power from Space |author=Lewis M. Fraas |conference=SSP Workshop Orlando FL, Dec 2015 |access-date=2016-05-23 |archive-url=https://web.archive.org/web/20160701131409/http://www.mtu.edu/ece/department/faculty/full-time/zekavat/SSP2015_fraas.pdf |archive-date=2016-07-01 |url-status=dead}}</ref>
Alternate satellite architecture: The typical satellite is a monolithic structure composed of a structural truss, one or more collectors, one or more transmitters, and occasionally primary and secondary reflectors. The entire structure may be gravity gradient stabilized. Alternative designs include:
* Swarms of smaller satellites: Some designs propose swarms of free-flying smaller satellites. This is the case with several laser designs, and appears to be the case with CALTECH's Flying Carpets.<ref>{{Cite web | url=https://climate.nasa.gov/news/2426/ |title = Will orbiting flying carpets light the world? |date=April 6, 2016 |first=Bob |last=Silberg |publisher=NASA}}</ref> For RF designs, an engineering constraint is the ] problem.
* Free floating components: ] has proposed an alternative to the monolithic structure where the primary reflector and transmission reflector are free-flying.<ref>{{Cite web | url=http://www.bldgblog.com/2009/04/space-based-storm-control/ |title = Space-Based Storm Control|date = 17 April 2009}}</ref>
* Spin stabilization: NASA explored a spin-stabilized thin film concept.
* Photonic laser thruster (PLT) stabilized structure: Young Bae has proposed that photon pressure may substitute for compressive members in large structures.<ref>{{Citation |last=Bae |first=Young |title=Photon Tether Formation Flight (PTFF) for Distributed and Fractionated Space Architectures |url=https://arc.aiaa.org/doi/abs/10.2514/6.2007-6084 |work=AIAA SPACE 2007 Conference & Exposition |year=2007 |publisher=American Institute of Aeronautics and Astronautics |doi=10.2514/6.2007-6084 |isbn=978-1-62410-016-1 |access-date=2022-05-10}}</ref>
Transmission: The most typical design for energy transmission is via an RF antenna at below 10&nbsp;GHz to a rectenna on the ground. Controversy exists between the benefits of Klystrons, Gyrotrons, Magnetrons and solid state. Alternate transmission approaches include:
* Laser: Lasers offer the advantage of much lower cost and mass to first power, however there is controversy regarding benefits of efficiency. Lasers allow for much smaller transmitting and receiving apertures. However, a highly concentrated beam has eye-safety, fire safety, and weaponization concerns. Proponents believe they have answers to all these concerns. A laser-based approach must also find alternate ways of coping with clouds and precipitation.
* Atmospheric waveguide: Some have proposed it may be possible to use a short pulse laser to create an atmospheric waveguide through which concentrated microwaves could flow.<ref>{{Cite web |url=https://apps.dtic.mil/sti/pdfs/ADA500916.pdf |title=Electromagnetic (EM) Wave Attachment To Laser Plasma Filaments |first=D. Clint |last=Friedman |date=May 2009}}</ref><ref>{{Cite journal | url=http://physics.aps.org/articles/v7/21 |title = A Waveguide Made of Hot Air|journal = Physics|date = 26 February 2014|volume = 7|last1 = Tzortzakis|first1 = Stelios|last2 = Couairon|first2 = Arnaud|pages = 21|doi = 10.1103/Physics.7.21|bibcode = 2014PhyOJ...7...21C|doi-access = free}}</ref><ref>{{Cite web|url=https://phys.technion.ac.il/index.php/en/events/details/1307-long-lived-atmospheric-waveguide-in-the-wake-of-laser-filaments|title=Events - "Long-lived Atmospheric Waveguide in the Wake of Laser Filaments"|website=phys.technion.ac.il |archive-date= 2017-02-16|archive-url=https://web.archive.org/web/20170216155921/https://phys.technion.ac.il/index.php/en/events/details/1307-long-lived-atmospheric-waveguide-in-the-wake-of-laser-filaments}}</ref>
* Nuclear synthesis: ] based in the inner solar system (whether in orbit or on a planet such as ]) could use solar energy to synthesize nuclear fuel from naturally occurring materials. While this would be highly inefficient using current technology (in terms of the amount of energy needed to manufacture the fuel compared to the amount of energy contained in the fuel) and would raise obvious ] issues, the basic technology upon which such an approach would rely on has been in use for decades, making this possibly the most reliable means of sending energy especially over very long distances - in particular, from the inner solar system to the outer solar system.
Materials and manufacturing: Typical designs make use of the developed industrial manufacturing system extant on Earth, and use Earth based materials both for the satellite and propellant. Variants include:
* Lunar materials: Designs exist for Solar Power Satellites that source >99% of materials from lunar regolith with very small inputs of "vitamins" from other locations. Using materials from the Moon is attractive because launch from the Moon is in theory far less complicated than from Earth. There is no atmosphere, and so components do not need to be packed tightly in an aeroshell and survive vibration, pressure and temperature loads. Launch may be via a magnetic mass driver and bypass the requirement to use propellant for launch entirely. Launch from the Moon the GEO also requires far less energy than from Earth's much deeper gravity well. Building all the solar power satellites to fully supply all the required energy for the entire planet requires less than one millionth of the mass of the Moon.
* Self-replication on the Moon: NASA explored a self-replicating factory on the Moon in the early 1980s.<ref>{{cite report |title=Replicating systems concepts: Self-replicating lunar factory and demonstration|date=November 1, 1982 |url=https://ntrs.nasa.gov/citations/19830007081 |publisher=NASA|access-date=January 31, 2023}}</ref> More recently, Justin Lewis-Webber proposed a method of speciated manufacture of core elements<ref>{{cite journal |doi=10.1089/space.2015.0041 |title=Lunar-Based Self-Replicating Solar Factory |journal=New Space |volume=4 |issue=1 |pages=53–62 |year=2016 |last1=Lewis-Weber |first1=Justin |bibcode=2016NewSp...4...53L }}</ref> based upon John Mankins SPS-Alpha design.<ref>{{Cite web | url=http://www.artemisinnovation.com/aboutus.html |title = ARTEMIS Innovation}}</ref><ref>{{Cite web|url=https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alpha.pdf|title=NASA.gov}}</ref>
* Asteroidal materials: Some asteroids are thought to have even lower Delta-V to recover materials than the Moon, and some particular materials of interest such as metals may be more concentrated or easier to access.
* In-space/in-situ manufacturing: With the advent of in-space additive manufacturing, concepts such as SpiderFab might allow mass launch of raw materials for local extrusion.<ref>{{Cite web |url=http://www.tethers.com/SpiderFab.html |title=Tethers Unlimited. SpiderFab Additive Manufacturing and Assembly On-Orbit |access-date=2016-05-23 |archive-date=2016-05-19 |archive-url=https://web.archive.org/web/20160519194353/http://www.tethers.com/SpiderFab.html |url-status=dead }}</ref>
Method of installation / Transportation of Material to Energy Collection Location: In the reference designs, component material is launched via well-understood chemical rockets (usually fully reusable launch systems) to LEO, after which either chemical or electrical propulsion is used to carry them to GEO. The desired characteristics for this system is very high mass-flow at low total cost. Alternate concepts include:
* Lunar chemical launch: ULA has recently showcased a concept for a fully re-usable chemical lander XEUS to move materials from the Lunar surface to LLO or GEO.<ref>{{Cite web |author=George Sowers |title=Transportation Architecture for Cislunar Space |publisher=United Launch Alliance |date=15 December 2015 |url=http://www.ulalaunch.com/uploads/docs/Published_Papers/Commercial_Space/SSP_12_15_sowers.pdf |access-date=2016-05-23 |archive-date=2016-05-07 |archive-url=https://web.archive.org/web/20160507083909/http://www.ulalaunch.com/uploads/docs/Published_Papers/Commercial_Space/SSP_12_15_sowers.pdf |url-status=dead }}</ref>
* Lunar ]: Launch of materials from the lunar surface using a system similar to an aircraft carrier electromagnetic catapult. An unexplored compact alternative would be the slingatron.
* ]: An equatorial or near-equatorial cable extends to and through the lagrange point. This is claimed by proponents to be lower in mass than a traditional mass driver.
* ]: A ribbon of pure carbon nanotubes extends from its center of gravity in Geostationary orbit, allowing climbers to climb up to GEO. Problems with this include the material challenge of creating a ribbon of such length (36,000 km!) with adequate strength, management of collisions with satellites and space debris, and lightning.
* MEO Skyhook: As part of an AFRL study, Roger Lenard proposed a MEO Skyhook. It appears that a gravity gradient-stabilized tether with its center of mass in MEO can be constructed of available materials. The bottom of the skyhook is close to the atmosphere in a "non-keplerian orbit". A re-usable rocket can launch to match altitude and speed with the bottom of the tether which is in a non-keplerian orbit (travelling much slower than typical orbital speed). The payload is transferred and it climbs the cable. The cable itself is kept from de-orbiting via electric propulsion and/or electromagnetic effects.
* ] launch / ]: John Powell has a concept for a very high mass-flow system. In a first-gen system, built into a mountain, accelerates a payload through an evacuated MAGLEV track. A small on-board rocket circularizes the payload.<ref>{{Cite web|url=https://startram.com/|title=Startram - The Startram Project|website=Startram}}</ref>
* Beamed energy launch: ] and ] both have concepts<ref>{{Cite thesis |url=https://thesis.library.caltech.edu/2405/ |doi=10.7907/T337-T709|year = 2006|last1 = Parkin|first1 = Kevin L.G.|title = The Microwave Thermal Thruster and Its Application to the Launch Problem|publisher = California Institute of Technology|type = PhD}}</ref> for ground-based irradiation of a mono-propellant launch vehicle using RF energy. The RF energy is absorbed and directly heats the propellant not unlike in NERVA-style nuclear-thermal. LaserMotive has a concept for a laser-based approach.


== Gallery ==
*'''2007''': The ]'s ] (NSSO) issues a report<ref></ref> on October 10, 2007 stating they intend to collect solar energy from space for use on Earth to help the United States' ongoing relationship with the ] and the battle for oil. The ] may be the first test ground for this new idea, even though it is in a low-earth orbit.


<gallery>
*'''2007''': In May 2007 a workshop is held at the US ] to review the current state of the SBSP market and technology.<ref> Date: May 14–16, 2007; Location: MIT, Cambridge MA</ref>
Image:Lunar base concept drawing s78 23252.jpg|A Lunar base with a mass driver (the long structure that goes toward the horizon). NASA conceptual illustration

Image:Advanced Automation for Space Missions figure 5-19.jpg|An artist's conception of a "self-growing" robotic lunar factory.
*'''2009''': Several companies announce future SBSP partnerships and commitments, including ] (PG&E) & ],<ref>{{cite news
File:Lunar solar power.jpg|Microwave reflectors on the moon and teleoperated robotic paving rover and crane.
| url= http://online.wsj.com/article/BT-CO-20090413-710658.html
File:Lunar solar crawler 2.png| "Crawler" traverses Lunar surface, smoothing, melting a top layer of regolith, then depositing elements of silicon PV cells directly on surface
| title= UPDATE: PG&E Looks To Outer Space For Solar Power (broken link)
File:Lunar solar crowler.png| Sketch of the Lunar Crawler to be used for fabrication of lunar solar cells on the surface of the Moon.
| last= Sweet | first= Cassandra
File:Solar.GIF|Shown here is an array of solar collectors that convert power into microwave beams directed toward Earth.
|date= April 13, 2009, | work= ] |publisher=
File:Solar power satellite from an asteroid.jpg|A solar power satellite built from a mined asteroid.
| accessdate= 2009-04-14 }} {{Dead link|date=October 2010|bot=H3llBot}}</ref><ref>
</gallery>
{{cite web
| url= http://www.next100.com/2009/04/space-solar-power-the-next-fro.php
| title= Space Solar Power: The Next Frontier?
| last= Marshall | first= Jonathan
|date= April 13, 2009 | work= Next 100 | publisher= ] (PG&E)
| accessdate= 2009-04-14 }}</ref><ref>
{{cite news
| url=http://www.msnbc.msn.com/id/30198977/
| title=Utility to buy orbit-generated electricity from Solaren in 2016, at no risk
| date=April 13, 2009 | publisher=]
| accessdate=2009-04-15 }}</ref> ] Corp. & ],<ref>http://www.bloomberg.com/apps/news?pid=newsarchive&sid=aJ529lsdk9HI</ref><ref>http://www.treehugger.com/files/2009/09/japan-space-based-solar-power-satellite-21-billions.php</ref> Space Energy, Inc.,<ref>http://science.slashdot.org/article.pl?sid=09/02/20/0149254</ref> and ].<ref>{{citation
| url=http://green.foxnews.com/2009/11/09/japan-to-beam-solar-power-from-space-on-lasers/
| title=Japan to Beam Solar Power from Space on Lasers
| publisher=]
| date=November 9, 2009}}</ref>

*'''2010''': Europe's ] announces SBSP plans.<ref>{{citation
| url=http://www.physorg.com/news183278937.html
| title=European space company wants solar power plant in space
| publisher=]
| date=January 21, 2010}}</ref><ref>{{citation
| url=http://news.bbc.co.uk/2/hi/science/nature/8467472.stm
| title=EADS Astrium develops space power concept
| publisher=]
| date=January 19, 2010}}</ref><ref>{{citation
| url=http://www.youtube.com/watch?v=KXRJA7BZmP0
| title=STRATFOR's founder and CEO discusses the push for space-based energy infrastructure (Video)
| publisher=]
| date=January 22, 2010}}</ref><ref>{{citation
| url=http://www.astrium.eads.net/node.php?articleid=6096
| title=Energy from space - made by Astrium
| publisher=]
| date=November 25, 2010}}</ref>

*'''2010''': Professors Andrea Massa and Giorgio Franceschetti announce a special session on the "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" at the 2010 ] International Symposium on Antennas and Propagation.<ref>{{citation
| url=http://www.apsursi2010.org/?m=page&id=47
| title=Special Session list
| publisher=''IEEE International Symposium on Antennas and Propagation''
| date=April 20, 2010}}</ref>

== In fiction ==
* Space stations transmitting solar power have appeared in science-fiction works like ]'s '']'' (1941), that centers around the troubles caused by ] operating the station. Asimov's short story "]" also features the use of SBSP to provide limitless energy for use on Earth.
* In the novel "Skyfall" (1976) by ] an attempt to launch the core of powersat from Cape Canaveral ends in disaster when the launch vehicle fails trapping the payload in a decaying orbit.
* Solar Power Satellites have also been seen in the work of author ]'s novels "Powersat" and "Colony".
* In ]'s '']'', an endgame 'building' that fulfills the same function as an SPS is the 'Orbital Power Transmitter' which provides every city that you own with a unit of energy per satellite launched, providing the city has an Aerospace Command building or your faction controls the ]. Building multiple Orbital Power Transmitters provides massive bonuses to energy generation and soon pay for themselves many times over.
* In a 1981 storyline from the ] comic book (issues #142-144), a rogue microwave transmission from a secret Solar Power Satellite is responsible for numerous deaths in Allentown, Iowa.
* In the computer games '']'' and '']'', plants that implemented solar satellite technology called microwave powerplants were available in the future. One disaster scenario involved the beam missing the receiver and hitting the city's infrastructure. The plant was discontinued in '']'' but several fan-made microwave powerplants were available on various ''SimCity 4'' fan sites.
* In the film '']'', a satellite weapon is disguised as a solar power satellite.
* In '']'', a solar power satellite array is constructed around the Earth and is used to harness ] for use. They play a critical plot role in the superpowers' ].
* In '']'', a solar power station is built on the Moon, and is used to supply energy via microwave to various mobile suits, to energise their powerful "Satellite Cannons".
* In '']'', space solar power is one of the lost technologies of the ancients.


== See also == == See also ==
{{Portal box|Renewable energy|Sustainable development|Energy}} {{Portal|Renewable energy|Outer space}}
{{Commons category|Space-based solar power}}
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]


* {{anl|Attitude dynamics and control}}
* ] equation for beamed wireless power efficiency
* {{anl|Friis transmission equation}}
* {{anl|Future energy development}}
* {{anl|Orbital station-keeping}}
* {{anl|Project Earth (TV series)}}
* {{anl|Solaris SBSP}}
* {{anl|Space mirror (climate engineering)}}
* {{anl|Znamya (satellite)|Znamya}}

== Notes ==
{{notelist}}


== References == == References ==
The ] maintains an extensive {{Webarchive|url=https://web.archive.org/web/20180414075904/http://www.nss.org/settlement/ssp/library/index.htm |date=2018-04-14 }} of all major historical documents and studies associated with space solar power, and {{Webarchive|url=https://web.archive.org/web/20160529144039/http://www.nss.org/settlement/ssp/#articles |date=2016-05-29 }}.{{Reflist|30em}}
{{Reflist|2}}


== External links == == External links ==
{{external links|date=September 2024}}
* in ]
{{commonscat}}
*

*
* in ]
* Space-based solar technology is the key to the world's energy and environmental future, writes ], a pioneer of the technology. * Space-based solar technology is the key to the world's energy and environmental future, writes ], a pioneer of the technology.
* , NASA 2004-212743, report by ] of NASA Glenn Research Center * , NASA 2004–212743, report by ] of NASA Glenn Research Center
* - the Japanese government hopes to assemble a space-based solar array by 2040. * - the Japanese government hopes to assemble a space-based solar array by 2040.
* - Space Energy, Inc. * - Space Energy, Inc.
* An article that covers the hurdles in the way of deploying a solar power satellite. * An article that covers the hurdles in the way of deploying a solar power satellite.
* Provides an overview of the technological and political developments needed to construct and utilize a multi-gigawatt power satellite. Also provides some perspective on the cost savings achieved by using ] in the construction of the satellite. * {{Webarchive|url=https://web.archive.org/web/20200925071846/https://www.permanent.com/p-sps.htm |date=2020-09-25 }} Provides an overview of the technological and political developments needed to construct and utilize a multi-gigawatt power satellite. Also provides some perspective on the cost savings achieved by using ] in the construction of the satellite.
* Reports on renewed institutional interest in SSP, and a lack of such interest in past decades. * Reports on renewed institutional interest in SSP, and a lack of such interest in past decades.
* Commercial space based solar power companies in Europe and the United States.
* Makoto Nagatomo, Susumu Sasaki and Yoshihiro Naruo * Makoto Nagatomo, Susumu Sasaki and Yoshihiro Naruo
* (] Science) * (] Science)
* http://www.nss.org/settlement/ssp/library/index.htm&nbsp;— The ]'s Space Solar Power Library * {{Webarchive|url=https://web.archive.org/web/20180414075904/http://www.nss.org/settlement/ssp/library/index.htm |date=2018-04-14 }} The ]'s Space Solar Power Library
* Special Session at the 2010 ''Festival delle Città Impresa'' featuring John Mankins (Artemis Innovation Management Solutions LLC, USA), Nobuyuki Kaya (], Japan), Sergio Garribba (], Italy), Lorenzo Fiori (] Group, Italy), Andrea Massa (], Italy) and Vincenzo Gervasio (], Italy). - History of SPS Developpements ] 2007
* 2010 IEEE International Symposium on Antennas and Propagation
*
* Special Session at the 2010 ''Festival delle Città Impresa'' featuring John Mankins (Artemis Innovation Management Solutions LLC, USA), Nobuyuki Kaya (], Japan), Sergio Garribba (Italian ], Italy), Lorenzo Fiori (] Group, Italy), Andrea Massa (], Italy) and Vincenzo Gervasio (], Italy). - History of SPS Developpements ] 2007
*

* {{cite web|url=https://time.com/6283990/scientists-solar-power-from-space/|magazine=]|title=Scientists Just Got A Step Closer to The Sci-Fi Reality of Building Solar Power Stations in Space|author=De La Garza, Alejandro|language=en-US|url-status=live|date=June 1, 2023|access-date=June 5, 2023|archive-date=June 5, 2023|archive-url=https://archive.today/20230605180652/https://time.com/6283990/scientists-solar-power-from-space/}}
== Videos ==
* 5-minute video about space-based solar power plants by the European Space Agency
* 20-minute streaming video from The Futures Channel that provides a "101" on space-based solar power
* 20-minute streaming video from The Futures Channel that provides a "101" on space-based solar power
* NewSpace 2010 Panel, 72 minutes
* SSI - Space Manufacturing 14 Panel - 2010 - 27 min * NewSpace 2010 Panel, 72 minutes
* Exploring New Frontiers for Tomorrow's Energy Needs * SSI&nbsp;– Space Manufacturing 14 Panel&nbsp;– 2010&nbsp;– 27 min
* Press Conference September 12, 2008 (71 minutes) {{Clarify|date=July 2011}} {{Who|date=July 2011}} ] * Exploring New Frontiers for Tomorrow's Energy Needs
* Press Conference September 12, 2008 (71 minutes) {{Clarify|date=July 2011}} {{Who|date=July 2011}} ]

* BBC/Lighthouse DEV Eye-safe Laser Based Power Beaming Demo
{{Space-based solar power}}


{{Solar energy}}
{{Photovoltaics}} {{Photovoltaics}}
{{emerging technologies|energy=yes}}
{{Inspace}}
{{Authority control}}


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Latest revision as of 16:19, 16 October 2024

Concept of collecting solar power in outer space and distributing it to EarthNot to be confused with Solar panels on spacecraft.
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NASA Integrated Symmetrical Concentrator SPS concept
A step by step diagram on space based solar power.
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Space-based solar power (SBSP or SSP) is the concept of collecting solar power in outer space with solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection and absorption by the atmosphere, the possibility of very little night, and a better ability to orient to face the Sun. Space-based solar power systems convert sunlight to some other form of energy (such as microwaves) which can be transmitted through the atmosphere to receivers on the Earth's surface.

Solar panels on spacecraft have been in use since 1958, when Vanguard I used them to power one of its radio transmitters; however, the term (and acronyms) above are generally used in the context of large-scale transmission of energy for use on Earth.

Various SBSP proposals have been researched since the early 1970s, but as of 2014 none is economically viable with the space launch costs. Some technologists propose lowering launch costs with space manufacturing or with radical new space launch technologies other than rocketry.

Besides cost, SBSP also introduces several technological hurdles, including the problem of transmitting energy from orbit. Since wires extending from Earth's surface to an orbiting satellite are not feasible with current technology, SBSP designs generally include the wireless power transmission with its associated conversion inefficiencies, as well as land use concerns for antenna stations to receive the energy at Earth's surface. The collecting satellite would convert solar energy into electrical energy, power a microwave transmitter or laser emitter, and transmit this energy to a collector (or microwave rectenna) on Earth's surface. Contrary to appearances in fiction, most designs propose beam energy densities that are not harmful if human beings were to be inadvertently exposed, such as if a transmitting satellite's beam were to wander off-course. But the necessarily vast size of the receiving antennas would still require large blocks of land near the end users. The service life of space-based collectors in the face of long-term exposure to the space environment, including degradation from radiation and micrometeoroid damage, could also become a concern for SBSP.

As of 2020, SBSP is being actively pursued by Japan, China, Russia, India, the United Kingdom, and the US.

In 2008, Japan passed its Basic Space Law which established space solar power as a national goal. JAXA has a roadmap to commercial SBSP.

In 2015, the China Academy for Space Technology (CAST) showcased its roadmap at the International Space Development Conference. In February 2019, Science and Technology Daily (科技日报, Keji Ribao), the official newspaper of the Ministry of Science and Technology of the People's Republic of China, reported that construction of a testing base had started in Chongqing's Bishan District. CAST vice-president Li Ming was quoted as saying China expects to be the first nation to build a working space solar power station with practical value. Chinese scientists were reported as planning to launch several small- and medium-sized space power stations between 2021 and 2025. In December 2019, Xinhua News Agency reported that China plans to launch a 200-tonne SBSP station capable of generating megawatts (MW) of electricity to Earth by 2035.

In May 2020, the US Naval Research Laboratory conducted its first test of solar power generation in a satellite. In August 2021, the California Institute of Technology (Caltech) announced that it planned to launch a SBSP test array by 2023, and at the same time revealed that Donald Bren and his wife Brigitte, both Caltech trustees, had been since 2013 funding the institute's Space-based Solar Power Project, donating over $100 million. A Caltech team successfully demonstrated beaming power to earth in 2023.

History

A laser pilot beam guides the microwave power transmission to a rectenna

In 1941, science fiction writer Isaac Asimov published the science fiction short story "Reason", in which a space station transmits energy collected from the Sun to various planets using microwave beams. The SBSP concept, originally known as satellite solar-power system (SSPS), was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g. from an SPS to Earth's surface) using microwaves from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna, on the ground.

Glaser then was a vice president at Arthur D. Little, Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems – chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space – it showed enough promise to merit further investigation and research.

Concept development and evaluation

Artist's concept of a solar power satellite in place. Shown is the assembly of a microwave transmission antenna. The solar power satellite was to be located in a geosynchronous orbit, 35,786 kilometres (22,236 mi) above the Earth's surface. NASA 1976

Between 1978 and 1986, the Congress authorized the Department of Energy (DoE) and NASA to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date (budget $50 million). Several reports were published investigating the engineering feasibility of such a project. They include:

  • Resource Requirements (Critical Materials, Energy, and Land)
  • Financial/Management Scenarios
  • Public Acceptance
  • State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities
  • Student Participation
  • Potential of Laser for SBSP Power Transmission
  • International Agreements
  • Centralization/Decentralization
  • Mapping of Exclusion Areas For Rectenna Sites
  • Economic and Demographic Issues Related to Deployment
  • Some Questions and Answers
  • Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers
  • Public Outreach Experiment
  • Power Transmission and Reception Technical Summary and Assessment
  • Space Transportation

Discontinuation

The project was not continued with the change in administrations after the 1980 United States elections. The Office of Technology Assessment concluded that "Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture."

In 1997, NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that the "US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO transportation down dramatically. This is, of course, an absolute requirement of space solar power."

Conversely, Pete Worden of NASA claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Worden referred to possible solutions as speculative and not available for decades at the earliest.

On November 2, 2012, China proposed a space collaboration with India that mentioned SBSP, "may be Space-based Solar Power initiative so that both India and China can work for long term association with proper funding along with other willing space faring nations to bring space solar power to earth."

Exploratory Research and Technology program

Main article: Space Solar Power Exploratory Research and Technology program
SERT Integrated Symmetrical Concentrator SPS concept.NASA

In 1999, NASA initiated its Space Solar Power Exploratory Research and Technology program (SERT) for the following purposes:

  • Perform design studies of selected flight demonstration concepts.
  • Evaluate studies of the general feasibility, design, and requirements.
  • Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
  • Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
  • Construct technology development and demonstration roadmaps for critical space solar power (SSP) elements.

SERT went about developing a solar power satellite (SPS) concept for a future gigawatt space power system, to provide electrical power by converting the Sun's energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar heat engines to convert sunlight into electricity. The program looked both at systems in Sun-synchronous orbit and geosynchronous orbit. Some of SERT's conclusions:

  • The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
  • The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic.
  • Renewable energy is a compelling approach, both philosophically and in engineering terms.
  • Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements.
  • Based on their Concept Definition Study, space solar power concepts may be ready to reenter the discussion.
  • Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin.
  • Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
  • The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of much lower cost access to space than has been available); however, the same can be said of many other advanced power technologies options.
  • Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.
  • Launch costs in the range of $100–$200 per kilogram of payload from low Earth orbit to Geosynchronous orbit are needed if SPS is to be economically viable.

Japan Aerospace Exploration Agency

The May 2014 IEEE Spectrum magazine carried a lengthy article "It's Always Sunny in Space" by Susumu Sasaki. The article stated, "It's been the subject of many previous studies and the stuff of sci-fi for decades, but space-based solar power could at last become a reality—and within 25 years, according to a proposal from researchers at the Tokyo-based Japan Aerospace Exploration Agency (JAXA)."

JAXA announced on 12 March 2015 that they wirelessly beamed 1.8 kilowatts 50 meters to a small receiver by converting electricity to microwaves and then back to electricity. This is the standard plan for this type of power. On 12 March 2015 Mitsubishi Heavy Industries demonstrated transmission of 10 kilowatts (kW) of power to a receiver unit located at a distance of 500 meters (m) away.

Advantages and disadvantages

Advantages

The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power:

  • It is always solar noon in space and full sun.
  • Collecting surfaces could receive much more intense sunlight, owing to the lack of obstructions such as atmospheric gasses, clouds, dust and other weather events. Consequently, the intensity in orbit is approximately 144% of the maximum attainable intensity on Earth's surface.
  • A satellite could be illuminated over 99% of the time and be in Earth's shadow a maximum of only 72 minutes per night at the spring and fall equinoxes at local midnight. Orbiting satellites can be exposed to a consistently high degree of solar radiation, generally for 24 hours per day, whereas earth surface solar panels currently collect power for an average of 29% of the day.
  • Power could be relatively quickly redirected directly to areas that need it most. A collecting satellite could possibly direct power on demand to different surface locations based on geographical baseload or peak load power needs.
  • Reduced plant and wildlife interference.
  • SBSP does not emit greenhouse gases unlike oil, gas, ethanol, and coal plants. Space based solar power also does not depend on or compete with scarce fresh water resources, unlike coal and nuclear plants.
  • SBSP generates forty times more than solar panels, and bring almost zero percent of hazardous waste to our environment. It also allows for electricity to be generated continuously, twenty four hours a day, ninety nine percent of the year.
  • If the clean energy that is provided from space-based solar power account for just five percent of our national energy consumption, our carbon footprint would be significantly reduced.

Disadvantages

The SBSP concept also has a number of problems:

  • The large cost of launching a satellite into space. For 6.5 kg/kW, the cost to place a power satellite in geosynchronous orbit (GEO) cannot exceed $200/kg if the power cost is to be competitive.
  • Microwave optic requires gigawatt scale to compensate for Airy disk beam spreading. Typically a 1 km disk in geosynchronous orbit transmitting at 2.45 GHz spreads out to 10 km at Earth distance.
  • Inability to constrain power transmission inside tiny beam angles. For example, a beam of 0.002 degrees (7.2 arc seconds) is required to stay within a one kilometer receiving antenna target from geostationary altitude. The most advanced directional wireless power transfer systems as of 2019 spread their half power beam width across at least 0.9 arc degrees.
  • Inaccessibility: Maintenance of an earth-based solar panel is relatively simple, but construction and maintenance on a solar panel in space would typically be done telerobotically. In addition to cost, astronauts working in GEO are exposed to unacceptably high radiation dangers and risk and cost about one thousand times more than the same task done telerobotically.
  • The space environment is hostile; PV panels (if used) suffer about eight times the degradation they would on Earth (except at orbits that are protected by the magnetosphere).
  • Space debris is a major hazard to large objects in space, particularly for large structures such as SBSP systems in transit through the debris below 2000 km. Already in 1978, astrophysicist Donald J. Kessler warned against a self-propagating collision cascade during the assembly of the SPS modules in LEO, which is now known as Kessler syndrome. Collision risk is much reduced in GEO since all the satellites are moving in the same direction at very close to the same speed.
  • The broadcast frequency of the microwave downlink (if used) would require isolating the SBSP systems away from other satellites. GEO space is already well used and would require coordinating with the ITU-R.
  • The large size and corresponding cost of the receiving station on the ground. The cost has been estimated at a billion dollars for 5 GW by SBSP researcher Keith Henson.
  • Energy losses during several phases of conversion from photons to electrons to photons back to electrons.
  • Waste heat disposal in space power systems is difficult to begin with, but becomes intractable when the entire spacecraft is designed to absorb as much solar radiation as possible. Traditional spacecraft thermal control systems such as radiative vanes may interfere with solar panel occlusion or power transmitters.
  • Decommissioning costs: The cost of deorbiting the satellites at the end of their service life to prevent them from exacerbating the orbital space debris problem due to impacts with asteroidal, cometary, and planetary debris is likely to be significant. While the future cost of imparting Delta-V is difficult to estimate, the amount of Delta-V that must be imparted to transfer a satellite from GEO to GTO is 1472 m/s. If, upon reentry, the disintegrating satellite would release hazardous chemicals into the Earth's atmosphere, then the additional expenses of disassembling the satellite and deorbiting the environmentally hazardous components within a space vehicle with downmass capabilities must be factored into the decommissioning costs.
  • Since these systems would be in space, they obviously would not be able to be controlled hands-on. Researchers, will need to create a way to maintain these systems autonomously, which could create some technical issues.
  • Research has also shown that an increase in population can increase congestion and ultimately could cause pieces of orbital debris, which was concluded from a test China had done with their satellite.

Design

Artist's concept of a solar disk on top of a LEO to GEO electrically powered space tug.

Space-based solar power essentially consists of three elements:

  1. collecting solar energy in space with reflectors or inflatable mirrors onto solar cells or heaters for thermal systems
  2. wireless power transmission to Earth via microwave or laser
  3. receiving power on Earth via a rectenna, a microwave antenna

The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as micrometeors and solar flares. Two basic methods of conversion have been studied: photovoltaic (PV) and solar dynamic (SD). Most analyses of SBSP have focused on photovoltaic conversion using solar cells that directly convert sunlight into electricity. Solar dynamic uses mirrors to concentrate light on a boiler. The use of solar dynamic could reduce mass per watt. Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth's surface, using either microwave or laser radiation at a variety of frequencies.

Microwave power transmission

William C. Brown demonstrated in 1964, during Walter Cronkite's CBS News program, a microwave-powered model helicopter that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW of power over a distance of 1 mile (1.6 km) at 9.6% efficiency.

Microwave power transmission of tens of kilowatts has been well proven by existing tests at Goldstone in California (1975) and Grand Bassin on Reunion Island (1997).

Comparison of laser and microwave power transmission. NASA diagram

More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountaintop in Maui and the island of Hawaii (92 miles away), by a team under John C. Mankins. Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it was demonstrated by the Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" held during the 2010 IEEE Symposium on Antennas and Propagation. In 2013, a useful overview was published, covering technologies and issues associated with microwave power transmission from space to ground. It includes an introduction to SPS, current research and future prospects. Moreover, a review of current methodologies and technologies for the design of antenna arrays for microwave power transmission appeared in the Proceedings of the IEEE.

Laser power beaming

Laser power beaming was envisioned by some at NASA as a stepping stone to further industrialization of space. In the 1980s, researchers at NASA worked on the potential use of lasers for space-to-space power beaming, focusing primarily on the development of a solar-powered laser. In 1989, it was suggested that power could also be usefully beamed by laser from Earth to space. In 1991, the SELENE project (SpacE Laser ENErgy) had begun, which included the study of laser power beaming for supplying power to a lunar base. The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project ended in 1993 before reaching a space-based demonstration.

Laser Solar Satellites

Laser Solar Satellites are smaller in size, meaning that they have to work as a group with other similar satellites. There are many pros to Laser Solar Satellites, specifically regarding their lower overall costs in comparison to other satellites. While the cost is lower than other satellites, there are various safety concerns, and other concerns regarding this satellite. Laser-emitting solar satellites only need to venture about 400 km into space, but because of their small generation capacity, hundreds or thousands of laser satellites would need to be launched in order to create a sustainable impact. A single satellite launch can range from fifty to four hundred million dollars. Lasers could be helpful for the energy from the sun harvested in space, to be returned back to Earth in order for terrestrial power demands to be met.

Orbital location

The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit, LEO requires several satellites before they are producing nearly continuous power.

Power beaming from geostationary orbit by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1 km diameter transmitting antenna and a 10 km diameter receiving rectenna for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption and even potential beam blockage by rain or water droplets. Because of the thinned array curse, it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.

A collection of LEO (low Earth orbit) space power stations has been proposed as a precursor to GEO (geostationary orbit) space-based solar power.

Earth-based receiver

The Earth-based rectenna would likely consist of many short dipole antennas connected via diodes. Microwave broadcasts from the satellite would be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity are also considerably greater. Rectennas would likely be several kilometers across.

In space applications

A laser SBSP could also power a base or vehicles on the surface of the Moon or Mars, saving on mass costs to land the power source. A spacecraft or another satellite could also be powered by the same means. In a 2012 report presented to NASA on space solar power, the author mentions another potential use for the technology behind space solar power could be for solar electric propulsion systems that could be used for interplanetary human exploration missions.

Launch costs

One problem with the SBSP concept is the cost of space launches and the amount of material that would need to be launched.

Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at an acceptable cost. Examples include ion thrusters or nuclear propulsion. Infrastructure including solar panels, power converters, and power transmitters will have to be built in order to begin the process. This will be extremely expensive and maintaining them will cost even more.

To give an idea of the scale of the problem, assuming a solar panel mass of 20 kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 metric tons, all of which would, in current circumstances, be launched from the Earth. This is, however, far from the state of the art for flown spacecraft, which as of 2015 was 150 W/kg (6.7 kg/kW), and improving rapidly. Very lightweight designs could likely achieve 1 kg/kW, meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. Beyond the mass of the panels, overhead (including boosting to the desired orbit and stationkeeping) must be added.

Launch costs for 4 GW to LEO
1 kg/kW 5 kg/kW 20 kg/kW
$1/kg (Minimum cost at ~$0.13/kWh power, 100% efficiency) $4M $20M $80M
$2000/kg (ex: Falcon Heavy) $8B $40B $160B
$10000/kg (ex: Ariane V) $40B $200B $800B

To these costs must be added the environmental impact of heavy space launch missions, if such costs are to be used in comparison to earth-based energy production. For comparison, the direct cost of a new coal or nuclear power plant ranges from $3 billion to $6 billion per GW (not including the full cost to the environment from CO2 emissions or storage of spent nuclear fuel, respectively).

Building from space

From lunar materials launched in orbit

Gerard O'Neill, noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the Moon. Launch costs from the Moon are potentially much lower than from Earth because of the lower gravity and lack of atmospheric drag. This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial upfront capital investment to establish mass drivers on the Moon. Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty solar power satellites of 10 GW capacity each.

In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al. published another route to manufacturing using lunar materials with much lower startup costs. This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under remote control of workers stationed on Earth. The high net energy gain of this proposal derives from the Moon's much shallower gravitational well.

Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in O'Neill's vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites. Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the lunar space elevator, first described by Jerome Pearson. It would require establishing silicon mining and solar cell manufacturing facilities on the Moon.

On the Moon

Physicist Dr David Criswell suggests the Moon is the optimum location for solar power stations, and promotes lunar-based solar power. The main advantage he envisions is construction largely from locally available lunar materials, using in-situ resource utilization, with a teleoperated mobile factory and crane to assemble the microwave reflectors, and rovers to assemble and pave solar cells, which would significantly reduce launch costs compared to SBSP designs. Power relay satellites orbiting around earth and the Moon reflecting the microwave beam are also part of the project. A demo project of 1 GW starts at $50 billion. The Shimizu Corporation use combination of lasers and microwave for the Luna Ring concept, along with power relay satellites.

From an asteroid

Asteroid mining has also been seriously considered. A NASA design study evaluated a 10,000-ton mining vehicle (to be assembled in orbit) that would return a 500,000-ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition. One proposal is to capture the asteroid Apophis into Earth orbit and convert it into 150 solar power satellites of 5 GW each or the larger asteroid 1999 AN10, which is 50 times the size of Apophis and large enough to build 7,500 5-gigawatt solar power satellites

Safety

The potential exposure of humans and animals on the ground to the high power microwave beams is a significant concern with these systems. At the Earth's surface, a suggested SPSP microwave beam would have a maximum intensity at its center, of 23 mW/cm. While this is less than 1/4 the solar irradiation constant, microwaves penetrate much deeper into tissue than sunlight, and at this level would exceed the current United States Occupational Safety and Health Act (OSHA) workplace exposure limits for microwaves at 10 mW/cm At 23 mW/cm, studies show humans experience significant deficits in spatial learning and memory. If the diameter of the proposed SPSP array is increased by 2.5x, the energy density on the ground increases to 1 W/cm. At this level, the median lethal dose for mice is 30-60 seconds of microwave exposure. While designing an array with 2.5x larger diameter should be avoided, the dual-use military potential of such a system is readily apparent.

With good array sidelobe design, outside the receiver may be less than the OSHA long-term levels as over 95% of the beam energy will fall on the rectenna. However, any accidental or intentional mis-pointing of the satellite could be deadly to life on Earth within the beam.

Exposure to the beam can be minimized in various ways. On the ground, assuming the beam is pointed correctly, physical access must be controllable (e.g., via fencing). Typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a Faraday Cage), which will intercept the microwaves. Other aircraft (balloons, ultralight, etc.) can avoid exposure by using controlled airspace, as is currently done for military and other controlled airspace. In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Suggestions have been made to locate rectennas offshore, but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.

A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. If the phase offset to the pilot is chosen the same for all elements, the transmitted beam should be centered precisely on the rectenna and have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused. Such a system would not focus its power beam very effectively anywhere that did not have a pilot beam transmitter. The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied.

Timeline

In the 20th century

  • 1941: Isaac Asimov published the science fiction short story "Reason," in which a space station transmits energy collected from the sun to various planets using microwave beams. "Reason" was published in the "Astounding Science Fiction" magazine.
  • 1968: Peter Glaser introduces the concept of a "solar power satellite" system with square miles of solar collectors in high geosynchronous orbit for collection and conversion of sun's energy into a microwave beam to transmit usable energy to large receiving antennas (rectennas) on Earth for distribution.
  • 1973: Peter Glaser is granted United States patent number 3,781,647 for his method of transmitting power over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
  • 1978–1981: The United States Department of Energy and NASA examine the solar power satellite (SPS) concept extensively, publishing design and feasibility studies.
  • 1987: Stationary High Altitude Relay Platform a Canadian experiment
  • 1995–1997: NASA conducts a "Fresh Look" study of space solar power (SSP) concepts and technologies.
  • 1998: The Space Solar Power Concept Definition Study (CDS) identifies credible, commercially viable SSP concepts, while pointing out technical and programmatic risks.
  • 1998: Japan's space agency begins developing a space solar power system (SSPS), a program that continues to the present day.
  • 1999: NASA's Space Solar Power Exploratory Research and Technology program (SERT, see below) begins.
  • 2000: John Mankins of NASA testifies in the U.S. House of Representatives, saying "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities. A technology roadmap has been developed that lays out potential paths for achieving all needed advances — albeit over several decades.

In the 21st century

  • 2001: NASDA (One of Japan's national space agencies before it became part of JAXA) announces plans to perform additional research and prototyping by launching an experimental satellite with 10 kilowatts and 1 megawatt of power.
  • 2003: ESA studies
  • 2007: The US Pentagon's National Security Space Office (NSSO) issues a report on October 10, 2007 stating they intend to collect solar energy from space for use on Earth to help the United States' ongoing relationship with the Middle East and the battle for oil. A demo plant could cost $10 billion, produce 10 megawatts, and become operational in 10 years.
  • 2007: In May 2007, a workshop is held at the US Massachusetts Institute of Technology (MIT) to review the current state of the SBSP market and technology.
  • 2010: Professors Andrea Massa and Giorgio Franceschetti announce a special session on the "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" at the 2010 Institute of Electrical and Electronics Engineers International Symposium on Antennas and Propagation.
  • 2010: The Indian Space Research Organisation and US' National Space Society launched a joint forum to enhance partnership in harnessing solar energy through space-based solar collectors. Called the Kalam-NSS Initiative after the former Indian President Dr APJ Abdul Kalam, the forum will lay the groundwork for the space-based solar power program which could see other countries joining in as well.
  • 2010: Sky's No Limit: Space-Based solar power, the next major step in the Indo-US strategic partnership? written by USAF Lt Col Peter Garretson was published at the Institute for Defence Studies and Analysis.
  • 2012: China proposed joint development between India and China towards developing a solar power satellite, during a visit by former Indian President Dr APJ Abdul Kalam.
  • 2015: The Space Solar Power Initiative (SSPI) is established between Caltech and Northrop Grumman Corporation. An estimated $17.5 million is to be provided over a three-year project for development of a space-based solar power system.
  • 2015: JAXA announced on 12 March 2015 that they wirelessly beamed 1.8 kilowatts 50 meters to a small receiver by converting electricity to microwaves and then back to electricity.
  • 2016: Lt Gen. Zhang Yulin, deputy chief of the armament development department of the Central Military Commission, suggested that China would next begin to exploit Earth-Moon space for industrial development. The goal would be the construction of space-based solar power satellites that would beam energy back to Earth.
  • 2016: A team with membership from the Naval Research Laboratory (NRL), Defense Advanced Projects Agency (DARPA), Air Force Air University, Joint Staff Logistics (J-4), Department of State, Makins Aerospace and Northrop Grumman won the Secretary of Defense (SECDEF) / Secretary of State (SECSTATE) / USAID Director's agency-wide D3 (Diplomacy, Development, Defense) Innovation Challenge with a proposal that the US must lead in space solar power. The proposal was followed by a vision video
  • 2016: Citizens for Space-Based Solar Power has transformed the D3 proposal into active petitions on the White House Website "America Must Lead the Transition to Space-Based Energy"and Change.org "USA Must Lead the Transition to Space-Based Energy" along with the following video.
  • 2016: Erik Larson and others from NOAA produce a paper "Global atmospheric response to emissions from a proposed reusable space launch system" The paper makes a case that up to 2 TW/year of power satellites could be constructed without intolerable damage to the atmosphere. Before this paper, there was concern that the NOx produced by reentry would destroy too much ozone.
  • 2016: Ian Cash of SICA Design proposes CASSIOPeiA (Constant Aperture, Solid State, Integrated, Orbital Phased Array) a new concept SPS Faculty Listing | Electrical and Computer Engineering
  • 2017: NASA selects five new research proposals focused on investments in space. The Colorado School of Mines focuses on "21st Century Trends in Space-Based Solar Power Generation and Storage."
  • 2019: Aditya Baraskar and Prof Toshiya Hanada from Space System Dynamic Laboratory, Kyushu University proposed Energy Orbit (E-Orbit), a small Space Solar Power Satellite constellation for power beaming between satellites in low earth orbit. A total of 1600 satellites to transmit 10 kilowatts of electricity in a 500 km radius at an altitude of 900 km.
  • 2019: China creates a test base for SBSP, and announces plan to launch a working megawatt-grade 200-tonne SBSP station by 2035.
  • 2020: US Naval Research Laboratory launches test satellite. Also the USAF has its Space Solar Power Incremental Demonstrations and Research Project (SSPIDR) planning to launch the ARACHNE test satellite. Arachne is due to launch in 2024.
  • 2021: Caltech announces that it planned to launch a SBSP test array by 2023.
  • 2022: The Space Energy Initiative in the UK announced to launch the first power station in space during the mid-2040s, to "provide 30 percent of the UK’s (greatly increased) electricity demand" and "to slash the UK’s dependence on fossil fuels" and foreign ties.
  • 2022: The European Space Agency proposed a program called SOLARIS to operate Solar Power Satellites from 2030.
  • 2023: Caltech's Space Solar Power Demonstrator (SSPD-1) beams "detectable power" to Earth.

Non-typical configurations and architectural considerations

The typical reference system-of-systems involves a significant number (several thousand multi-gigawatt systems to service all or a significant portion of Earth's energy requirements) of individual satellites in GEO. The typical reference design for the individual satellite is in the 1-10 GW range and usually involves planar or concentrated solar photovoltaics (PV) as the energy collector / conversion. The most typical transmission designs are in the 1–10 GHz (2.45 or 5.8 GHz) RF band where there are minimum losses in the atmosphere. Materials for the satellites are sourced from, and manufactured on Earth and expected to be transported to LEO via re-usable rocket launch, and transported between LEO and GEO via chemical or electrical propulsion. In summary, the architecture choices are:

  • Location = GEO
  • Energy Collection = PV
  • Satellite = Monolithic Structure
  • Transmission = RF
  • Materials & Manufacturing = Earth
  • Installation = RLVs to LEO, Chemical to GEO

There are several interesting design variants from the reference system:

Alternate energy collection location: While GEO is most typical because of its advantages of nearness to Earth, simplified pointing and tracking, very small time in occultation, and scalability to meet all global demand several times over, other locations have been proposed:

  • Sun Earth L1: Robert Kennedy III, Ken Roy & David Fields have proposed a variant of the L1 sunshade called "Dyson Dots" where a multi-terawatt primary collector would beam energy back to a series of LEO sun-synchronous receiver satellites. The much farther distance to Earth requires a correspondingly larger transmission aperture.
  • Lunar surface: David Criswell has proposed using the Lunar surface itself as the collection medium, beaming power to the ground via a series of microwave reflectors in Earth Orbit. The chief advantage of this approach would be the ability to manufacture the solar collectors in-situ without the energy cost and complexity of launch. Disadvantages include the much longer distance, requiring larger transmission systems, the required "overbuild" to deal with the lunar night, and the difficulty of sufficient manufacturing and pointing of reflector satellites.
  • MEO: MEO systems have been proposed for in-space utilities and beam-power propulsion infrastructures. For example, see Royce Jones' paper.
  • Highly elliptical orbits: Molniya, Tundra, or Quazi Zenith orbits have been proposed as early locations for niche markets, requiring less energy to access and providing good persistence.
  • Sun-sync LEO: In this near Polar Orbit, the satellites precess at a rate that allows them to always face the Sun as they rotate around Earth. This is an easy to access orbit requiring far less energy, and its proximity to Earth requires smaller (and therefore less massive) transmitting apertures. However disadvantages to this approach include having to constantly shift receiving stations, or storing energy for a burst transmission. This orbit is already crowded and has significant space debris.
  • Equatorial LEO: Japan's SPS 2000 proposed an early demonstrator in equatorial LEO in which multiple equatorial participating nations could receive some power.
  • Earth's surface: Narayan Komerath has proposed a space power grid where excess energy from an existing grid or power plant on one side of the planet can be passed up to orbit, across to another satellite and down to receivers.

Energy collection: The most typical designs for solar power satellites include photovoltaics. These may be planar (and usually passively cooled), concentrated (and perhaps actively cooled). However, there are multiple interesting variants.

  • Solar thermal: Proponents of solar thermal have proposed using concentrated heating to cause a state change in a fluid to extract energy via rotating machinery followed by cooling in radiators. Advantages of this method might include overall system mass (disputed), eliminating degradation due to solar-wind damage, and radiation tolerance. One recent thermal solar power satellite design by Keith Henson and others has been visualized here. Thermal Space Solar Power concept A related concept is here: Beamed Energy Bootstrapping The proposed radiators are thin wall platic tube filled with low pressure (2.4 kPa) and temperature (20 deg C) steam.
  • Solar pumped laser: Japan has pursued a solar-pumped laser, where sunlight directly excites the lasing medium used to create the coherent beam to Earth.
  • Stellaser: A hypothetical concept of a very large laser where a star provides both the lasing energy and the lasing medium, producing a steerable energy beam of unrivaled power.
  • Fusion decay: This version of a power-satellite is not "solar". Rather, the vacuum of space is seen as a "feature not a bug" for traditional fusion. Per Paul Werbos, after fusion even neutral particles decay to charged particles which in a sufficiently large volume would allow direct conversion to current.
  • Solar wind loop: Also called a Dyson–Harrop satellite. Here the satellite makes use not of the photons from the Sun but rather the charged particles in the solar wind which via electro-magnetic coupling generate a current in a large loop.
  • Direct mirrors: Early concepts for direct mirror re-direction of light to planet Earth suffered from the problem that rays coming from the sun are not parallel but are expanding from a disk and so the size of the spot on the Earth is quite large. Lewis Fraas has explored an array of parabolic mirrors to augment existing solar arrays.

Alternate satellite architecture: The typical satellite is a monolithic structure composed of a structural truss, one or more collectors, one or more transmitters, and occasionally primary and secondary reflectors. The entire structure may be gravity gradient stabilized. Alternative designs include:

  • Swarms of smaller satellites: Some designs propose swarms of free-flying smaller satellites. This is the case with several laser designs, and appears to be the case with CALTECH's Flying Carpets. For RF designs, an engineering constraint is the thinned array problem.
  • Free floating components: Solaren has proposed an alternative to the monolithic structure where the primary reflector and transmission reflector are free-flying.
  • Spin stabilization: NASA explored a spin-stabilized thin film concept.
  • Photonic laser thruster (PLT) stabilized structure: Young Bae has proposed that photon pressure may substitute for compressive members in large structures.

Transmission: The most typical design for energy transmission is via an RF antenna at below 10 GHz to a rectenna on the ground. Controversy exists between the benefits of Klystrons, Gyrotrons, Magnetrons and solid state. Alternate transmission approaches include:

  • Laser: Lasers offer the advantage of much lower cost and mass to first power, however there is controversy regarding benefits of efficiency. Lasers allow for much smaller transmitting and receiving apertures. However, a highly concentrated beam has eye-safety, fire safety, and weaponization concerns. Proponents believe they have answers to all these concerns. A laser-based approach must also find alternate ways of coping with clouds and precipitation.
  • Atmospheric waveguide: Some have proposed it may be possible to use a short pulse laser to create an atmospheric waveguide through which concentrated microwaves could flow.
  • Nuclear synthesis: Particle accelerators based in the inner solar system (whether in orbit or on a planet such as Mercury) could use solar energy to synthesize nuclear fuel from naturally occurring materials. While this would be highly inefficient using current technology (in terms of the amount of energy needed to manufacture the fuel compared to the amount of energy contained in the fuel) and would raise obvious nuclear safety issues, the basic technology upon which such an approach would rely on has been in use for decades, making this possibly the most reliable means of sending energy especially over very long distances - in particular, from the inner solar system to the outer solar system.

Materials and manufacturing: Typical designs make use of the developed industrial manufacturing system extant on Earth, and use Earth based materials both for the satellite and propellant. Variants include:

  • Lunar materials: Designs exist for Solar Power Satellites that source >99% of materials from lunar regolith with very small inputs of "vitamins" from other locations. Using materials from the Moon is attractive because launch from the Moon is in theory far less complicated than from Earth. There is no atmosphere, and so components do not need to be packed tightly in an aeroshell and survive vibration, pressure and temperature loads. Launch may be via a magnetic mass driver and bypass the requirement to use propellant for launch entirely. Launch from the Moon the GEO also requires far less energy than from Earth's much deeper gravity well. Building all the solar power satellites to fully supply all the required energy for the entire planet requires less than one millionth of the mass of the Moon.
  • Self-replication on the Moon: NASA explored a self-replicating factory on the Moon in the early 1980s. More recently, Justin Lewis-Webber proposed a method of speciated manufacture of core elements based upon John Mankins SPS-Alpha design.
  • Asteroidal materials: Some asteroids are thought to have even lower Delta-V to recover materials than the Moon, and some particular materials of interest such as metals may be more concentrated or easier to access.
  • In-space/in-situ manufacturing: With the advent of in-space additive manufacturing, concepts such as SpiderFab might allow mass launch of raw materials for local extrusion.

Method of installation / Transportation of Material to Energy Collection Location: In the reference designs, component material is launched via well-understood chemical rockets (usually fully reusable launch systems) to LEO, after which either chemical or electrical propulsion is used to carry them to GEO. The desired characteristics for this system is very high mass-flow at low total cost. Alternate concepts include:

  • Lunar chemical launch: ULA has recently showcased a concept for a fully re-usable chemical lander XEUS to move materials from the Lunar surface to LLO or GEO.
  • Lunar mass driver: Launch of materials from the lunar surface using a system similar to an aircraft carrier electromagnetic catapult. An unexplored compact alternative would be the slingatron.
  • Lunar space elevator: An equatorial or near-equatorial cable extends to and through the lagrange point. This is claimed by proponents to be lower in mass than a traditional mass driver.
  • Space elevator: A ribbon of pure carbon nanotubes extends from its center of gravity in Geostationary orbit, allowing climbers to climb up to GEO. Problems with this include the material challenge of creating a ribbon of such length (36,000 km!) with adequate strength, management of collisions with satellites and space debris, and lightning.
  • MEO Skyhook: As part of an AFRL study, Roger Lenard proposed a MEO Skyhook. It appears that a gravity gradient-stabilized tether with its center of mass in MEO can be constructed of available materials. The bottom of the skyhook is close to the atmosphere in a "non-keplerian orbit". A re-usable rocket can launch to match altitude and speed with the bottom of the tether which is in a non-keplerian orbit (travelling much slower than typical orbital speed). The payload is transferred and it climbs the cable. The cable itself is kept from de-orbiting via electric propulsion and/or electromagnetic effects.
  • MAGLEV launch / StarTram: John Powell has a concept for a very high mass-flow system. In a first-gen system, built into a mountain, accelerates a payload through an evacuated MAGLEV track. A small on-board rocket circularizes the payload.
  • Beamed energy launch: Kevin Parkin and Escape Dynamics both have concepts for ground-based irradiation of a mono-propellant launch vehicle using RF energy. The RF energy is absorbed and directly heats the propellant not unlike in NERVA-style nuclear-thermal. LaserMotive has a concept for a laser-based approach.

Gallery

  • A Lunar base with a mass driver (the long structure that goes toward the horizon). NASA conceptual illustration A Lunar base with a mass driver (the long structure that goes toward the horizon). NASA conceptual illustration
  • An artist's conception of a "self-growing" robotic lunar factory. An artist's conception of a "self-growing" robotic lunar factory.
  • Microwave reflectors on the moon and teleoperated robotic paving rover and crane. Microwave reflectors on the moon and teleoperated robotic paving rover and crane.
  • "Crawler" traverses Lunar surface, smoothing, melting a top layer of regolith, then depositing elements of silicon PV cells directly on surface "Crawler" traverses Lunar surface, smoothing, melting a top layer of regolith, then depositing elements of silicon PV cells directly on surface
  • Sketch of the Lunar Crawler to be used for fabrication of lunar solar cells on the surface of the Moon. Sketch of the Lunar Crawler to be used for fabrication of lunar solar cells on the surface of the Moon.
  • Shown here is an array of solar collectors that convert power into microwave beams directed toward Earth. Shown here is an array of solar collectors that convert power into microwave beams directed toward Earth.
  • A solar power satellite built from a mined asteroid. A solar power satellite built from a mined asteroid.

See also

Notes

  1. An increase in space array diameter of 2.5x increases the array element count by 6.25x, which increases total power transmitted by this factor. In addition for a coherent microwave beam, the ground spot area decreases by 6.25x, therefore the power density on ground increases by 6.25 = 40x. This increases the proposed 23 W/cm to about 1 W/cm

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