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| A '''geosynchronous orbit''' is an ] that has the same orbital period as the body it orbits (usually the ] but geosynchronous orbits exist around all moons, planets and suns that have sufficient rotational speed for an orbit to be maintained above the surface). | |||
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| If a geosynchronous orbit is circular and equatorial then it is also a ], and will maintain the same position relative to the body it rotates around. If one could see a satellite in geostationary orbit it would appear to hover in the same position. | |||
| A circular geosynchronous orbit in the plane of the Earth's equator has a radius of approximately 42,164 km (from the center of the Earth), |
A circular geosynchronous orbit in the plane of the Earth's equator has a radius of approximately 42,164 km (from the center of the Earth), approximately ] above ]. | ||
| This can be demonstrated analytically by application of the Law of ] and the physics of ]. Drawing the ] and using the analysis methods of ] and ] allows the determination of the distance from Earth's center of mass which will satisfy this specified operating condition. | This can be demonstrated analytically by application of the Law of ] and the physics of ]. Drawing the ] and using the analysis methods of ] and ] allows the determination of the distance from Earth's center of mass which will satisfy this specified operating condition. | ||
| ==Circular geosynchronous orbits== | ==Circular geosynchronous orbits== | ||
| A perfect stable geostationary orbit is an ideal that can only be approximated. In practice the satellite will drift out of this orbit (caused by forces such as the ], and the ] effect of the moon) and thrusters are used to maintain the orbit. | |||
| ⚫ | The "]" is the part of space approximately 35,790 km directly above ]'s ] where near-geostationary orbits may be achieved, named after ] writer and scientist ] who wrote about this belt in ]. | ||
| An ideal circular orbit that kept the satellite over a single point on the Earth's equator at all times is called a ]. | |||
| Geostationary orbits can only be acheived very close to the ring 35,790 km directly above the equator. All other circular non-active geosynchronous orbits will cross the geostationary orbit and possibly collide with satellites there. In practice this means that all geostationary satellites have to exist on this ring, which poses problems for satellites needing to be decommisioned at the end of their service life (for example when they run out of thrust fuel). | |||
| In general, a perfect stable geostationary orbit is an ideal that can only be approximated. | |||
| In practice, several different practical methods of station keeping allow satellites to remain over a required region of the Earth's surface. | |||
| ⚫ | ==Other geosynchronous orbits== | ||
| ⚫ | The |
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| ⚫ | ''] orbits'' can be and are designed for ]s that keep the satellite within view of its assigned ground stations or receivers. A satellite in an elliptical geosynchronous orbit will appear to oscillate in the sky from the viewpoint of a ground station, and satellites in highly elliptical orbits must be tracked by steerable ]s. | ||
| Clarke's and ]'s visions of geostationary ]s were made a reality in ] with the launch of ]. | |||
| Theoretically an ''active geosynchronous'' orbit can be maintained if forces other than gravity are also used to maintain the orbit, such as a ]. Such a ] can be geosynchronous in an orbit different (higher, lower, more or less elliptical, or some other path) from the ] orbit formed by a gravitational body. Such devices are still theoretical. | |||
| ==Elliptical geosynchronous orbits== | |||
| A further form of geosynchronous orbit is obtained by the theoretical ] in which one end of the structure is tethered to the ground, maintaining a longer orbital period than by gravity alone. | |||
| Elliptical orbits can be and are designed for ]s that keep the satellite within view of its assigned ground stations or receivers. | |||
| ⚫ | ==History== | ||
| ⚫ | A satellite in an elliptical geosynchronous orbit will appear to oscillate in the sky from the viewpoint of a ground station, and satellites in highly elliptical orbits must be tracked by steerable ]s. | ||
| The first communications satellite placed in a geosynchronous orbit was ], launched in 1963. Geosynchronous orbits have been in common use ever since including satellite television. Initially geostationary satellites also carried telephone calls but are no longer used for voice communication, partly due to the inherent disconcerting delay in getting information to the satellite and back (it takes light or radio about a quarter of a second to make the round trip.) | |||
| ==External link== | |||
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| ⚫ | == |
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| Theoretically ] can use active thrust to balance a portion of the gravity forces experienced. Thus it can be "geo synchronous" in an orbit different from the traditional definition established in the early era of initial space exploration activities. | |||
| ⚫ | ==History== | ||
| The first communications satellite placed in a geosynchronous orbit was ], launched in 1963. Geosynchronous orbits have been in common use ever since. | |||
Revision as of 18:45, 30 April 2004
A geosynchronous orbit is an orbit that has the same orbital period as the body it orbits (usually the Earth but geosynchronous orbits exist around all moons, planets and suns that have sufficient rotational speed for an orbit to be maintained above the surface).
If a geosynchronous orbit is circular and equatorial then it is also a geostationary orbit, and will maintain the same position relative to the body it rotates around. If one could see a satellite in geostationary orbit it would appear to hover in the same position.
A circular geosynchronous orbit in the plane of the Earth's equator has a radius of approximately 42,164 km (from the center of the Earth), approximately 35,790 km (22,240 statute miles) above mean sea level.
This can be demonstrated analytically by application of the Law of Gravity and the physics of centripetal acceleration. Drawing the free body diagram and using the analysis methods of engineering dynamics and Physics allows the determination of the distance from Earth's center of mass which will satisfy this specified operating condition.
Circular geosynchronous orbits
A perfect stable geostationary orbit is an ideal that can only be approximated. In practice the satellite will drift out of this orbit (caused by forces such as the solar wind, and the gravitational effect of the moon) and thrusters are used to maintain the orbit.
The "Clarke Belt" is the part of space approximately 35,790 km directly above Earth's equator where near-geostationary orbits may be achieved, named after Science fiction writer and scientist Arthur C. Clarke who wrote about this belt in 1945.
Geostationary orbits can only be acheived very close to the ring 35,790 km directly above the equator. All other circular non-active geosynchronous orbits will cross the geostationary orbit and possibly collide with satellites there. In practice this means that all geostationary satellites have to exist on this ring, which poses problems for satellites needing to be decommisioned at the end of their service life (for example when they run out of thrust fuel).
Other geosynchronous orbits
Elliptical orbits can be and are designed for communications satellites that keep the satellite within view of its assigned ground stations or receivers. A satellite in an elliptical geosynchronous orbit will appear to oscillate in the sky from the viewpoint of a ground station, and satellites in highly elliptical orbits must be tracked by steerable ground stations.
Theoretically an active geosynchronous orbit can be maintained if forces other than gravity are also used to maintain the orbit, such as a solar sail. Such a statite can be geosynchronous in an orbit different (higher, lower, more or less elliptical, or some other path) from the conic section orbit formed by a gravitational body. Such devices are still theoretical.
A further form of geosynchronous orbit is obtained by the theoretical space elevator in which one end of the structure is tethered to the ground, maintaining a longer orbital period than by gravity alone.
History
The first communications satellite placed in a geosynchronous orbit was Syncom 2, launched in 1963. Geosynchronous orbits have been in common use ever since including satellite television. Initially geostationary satellites also carried telephone calls but are no longer used for voice communication, partly due to the inherent disconcerting delay in getting information to the satellite and back (it takes light or radio about a quarter of a second to make the round trip.)