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Vanguard 2

A model of the Vanguard 2 satellite in front of the Goddard Space Flight Center.
Names	Vanguard Space Launch Vehicle-4
Mission type	Weather satellite Air Density Experiment
Operator	Naval Research Laboratory
Harvard designation	1959 Alpha 1
COSPAR ID	1959-001A
SATCAT no.	00011
Mission duration	Weather observation: 19 days (achieved) 65 years, 10 months and 2 days (in orbit)
Spacecraft properties
Spacecraft type	Vanguard 2E
Bus	Vanguard
Manufacturer	Naval Research Laboratory
Launch mass	10.75 kg (23.7 lb)
Dimensions	50.8 cm (20.0 in) of diameter
Start of mission
Launch date	17 February 1959, 15:55:02 GMT
Rocket	Vanguard SLV-4
Launch site	Cape Canaveral, LC-18A
Contractor	Glenn L. Martin Company
End of mission
Last contact	15 March 1959
Decay date	2259 (estimated) ~ 300 years orbital lifetime
Orbital parameters
Reference system	Geocentric orbit
Regime	Medium Earth orbit
Perigee altitude	559 km (347 mi)
Apogee altitude	3,320 km (2,060 mi)
Inclination	32.88°
Period	125.80 minutes
Instruments
Optical scanner Radio beacon
Project Vanguard← Vanguard SLV-3Vanguard SLV-5 →

Vanguard 2 (or Vanguard 2E before launch) is an Earth-orbiting satellite launched 17 February 1959 at 15:55:02 GMT, aboard a Vanguard SLV-4 rocket as part of the United States Navy's Project Vanguard. The satellite was designed to measure cloud cover distribution over the daylight portion of its orbit, for a period of 19 days, and to provide information on the density of the atmosphere for the lifetime of its orbit (about 300 years). As the first weather satellite and one of the first orbital space missions, the launch of Vanguard 2 was an important milestone in the Space Race between the United States and the Soviet Union. Vanguard 2 remains in orbit.

Previous satellites

Before the successful 1959 launch of the satellite that became known as Vanguard 2, multiple attempted launches of satellites named "Vanguard 2" were made in 1958. All of these launches failed to reach orbit. The satellites that failed to reach orbit were:

• Vanguard 2A: launched 29 April 1958, by the Vanguard TV-5 rocket
• Vanguard 2B: launched 28 May 1958, by the Vanguard SLV-1 rocket
• Vanguard 2C: launched 26 June 1958, by the Vanguard SLV-2 rocket
• Vanguard 2D: launched 26 September 1958, by the Vanguard SLV-3 rocket

The satellite whose launch was successful and that became known as the Vanguard 2 was the Vanguard 2E.

Spacecraft

The spacecraft is a magnesium sphere 50.8 cm (20.0 in) in diameter. It contains two optical telescopes with two photocells. The sphere was internally gold-plated, and externally covered with an aluminum deposit coated with silicon oxide of sufficient thickness to provide thermal control for the instrumentation.

Radio communication was provided by a 1 watt, 108.03 MHz telemetry transmitter and a 10 mW, 108 MHz beacon transmitter that sent a continuous signal for tracking purposes. A command receiver was used to activate a tape recorder that relayed telescope experiment data to the telemetry transmitter.

The power supply for the instrumentation was provided by mercury batteries.

Instruments

Optical scanner

The optical scanner experiment was designed to obtain cloud cover data between the equator and 35° to 45° N latitude. As the satellite circled Earth, two photocells, located at the focus of two optical telescopes aimed in diametrically opposite directions, measured the intensity of sunlight reflected from clouds (about 80%), from land masses (15 to 20%), and from sea areas (5%). The satellite motion and rotation caused the photocells to scan the Earth in successive "lines" (akin to a whisk broom scanner). Separate solar batteries turned on a recorder only when the Earth beneath the satellite was in sunlight and about 50 minutes of data per orbit were obtained. The measured reflection intensities were stored on tape. Ground stations interrogated the satellite by signaling its command receiver, which caused the entire tape to be played back in 60 seconds. The tape was then erased and rewound. For the planned 19 days of the weather experiment, the equipment functioned normally. The satellite was spin-stabilized at 50 rpm, but the optical instrument's data was poor because of an unsatisfactory orientation of the spin axis.

Satellite drag atmospheric density

Because of its symmetrical shape, Vanguard 2 was selected by the experimenters for use in determining upper atmospheric densities as a function of altitude, latitude, season, and solar activity. As the spacecraft continuously orbited, it would lead its predicted positions slightly, accumulating greater and greater advance as it spiraled lower and faster due to the drag of the residual atmosphere. By measuring the rate and timing of orbital shifts, the relevant atmosphere's parameters could be back-calculated knowing the body's drag properties. It was determined that atmospheric pressures, and thus drag and orbital decay, were higher than anticipated, as Earth's upper atmosphere gradually tapered into space.

This experiment was planned in great detail prior to launch. Initial Naval Research Laboratory (NRL) proposals for Project Vanguard included conical satellite bodies; this eliminated the need for a separate fairing and ejection mechanisms, and their associated weight and failure modes. Radio tracking would gather data and establish a position. Early in the program, optical tracking (with a Baker-Nunn camera network and human spotters) was added. A panel of scientists proposed changing the design to spheres, at least 50.8 cm (20.0 in) in diameter and hopefully 76 cm (30 in). A sphere would have a constant optical reflection, and constant coefficient of drag, based on size alone, while a cone would vary with orientation. James Van Allen proposed a cylinder, which eventually flew. The Naval Research Lab finally accepted 16 cm (6.3 in) spheres as a "test vehicle", with 50.8 cm (20.0 in) for follow-on satellites. The payload weight savings, from reduced size as well as decreased instrumentation in the early satellites, was considered acceptable for the initial launches. Afterwards, the later Vanguard rockets had some test instrumentation removed, lightening them enough for the 50.8 cm bodies.

Post mission

After the scientific mission ended, both Vanguard 2 and the upper stage of the rocket used to launch the satellite became derelict objects that would continue to orbit Earth for many years. Both objects remain in orbit. As Vanguard 1, Vanguard 2, and Vanguard 3 are still orbiting with their drag properties essentially unchanged, they form a baseline data set on the atmosphere of Earth that is over 60 years old and continuing. Vanguard 2 has an expected orbital lifetime of 300 years.

See also

• Timeline of first images of Earth from space
• Vanguard 1
• Sputnik 1
• Sputnik (rocket)
• Weather satellite
• Timeline of artificial satellites and space probes

References

1. McDowell, Jonathan. "Launch Log". Jonathan's Space Report. Archived from the original on 13 November 2009. Retrieved 3 February 2021.
2. ^ "Vanguard 2 1959-001A". NASA. 14 May 2020. Archived from the original on 9 March 2021. Retrieved 3 February 2021. This article incorporates text from this source, which is in the public domain.
3. "VANGUARD 2 Satellite details 1959-001A NORAD 11". N2YO. 24 January 2015. Archived from the original on 27 January 2021. Retrieved 3 February 2021.
4. "VANGUARD – A HISTORY, CHAPTER 12, SUCCESS – AND AFTER". NASA. Archived from the original on 9 May 2008. Retrieved 12 July 2017. This article incorporates text from this source, which is in the public domain.
5. ^ "Vanguard Project". U.S. Naval Research Laboratory. 1 February 2010. Archived from the original on 23 December 2015. Retrieved 9 February 2016. This article incorporates text from this source, which is in the public domain.
6. NASA, History, Chapter two, SATELLITES Archived 4 November 2004 at the Wayback Machine This article incorporates text from this source, which is in the public domain.
7. Brian Dunbar. "Interesting Goddard Facts and Firsts". NASA (Goddard). Archived from the original on 25 December 2015. Retrieved 9 February 2016. This article incorporates text from this source, which is in the public domain.
8. Janice Hill (1991). Weather From Above: America's Meteorological Satellites. Smithsonian Institution. pp. 4–7. ISBN 0-87474-394-X.
9. McLaughlin Green, Constance; Lomask, Milton (1970). Vanguard: A History (PDF). The NASA Historical Series. NASA. pp. 282–287. Archived (PDF) from the original on 7 October 2021. Retrieved 15 February 2022.
10. Vanguard 2, astronautix.com Archived 2016-02-10 at the Wayback Machine
11. Project Vanguard: The NASA History, By Constance McLaughlin Green, Milton Lomask
12. "Experiment 1: Optical scanner 1959-001A". NASA. 14 May 2020. Archived from the original on 9 March 2021. Retrieved 3 February 2021. This article incorporates text from this source, which is in the public domain.
13. "Satellite Drag Atmospheric Density". NASA (Goddard). 14 May 2020. Archived from the original on 7 February 2021. Retrieved 3 February 2021. This article incorporates text from this source, which is in the public domain.
14. ^ "Atmospheric Density Values from Satellite Drag Measurements". NASA. 14 May 2020. Archived from the original on 8 March 2021. Retrieved 3 February 2021. This article incorporates text from this source, which is in the public domain.
15. C. McLaughlin Green, M. Lomask, "Vanguard, A History Archived 20 December 2017 at the Wayback Machine", Chapter 5, Battle over Vehicle Specifications NASA SP-4202 This article incorporates text from this source, which is in the public domain.

External links

• Historic newsreel footage of the Vanguard II Satellite

• Spacecraft launched in 1959
• 1959 in the United States
• Derelict satellites orbiting Earth
• Project Vanguard
• Weather satellites of the United States