Geosynchronous orbit
A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered
A special case of geosynchronous orbit is the
History
In 1929,
In technical terminology, the geosynchronous orbits are often referred to as geostationary if they are roughly over the equator, but the terms are used somewhat interchangeably.[8][9] Specifically, geosynchronous Earth orbit (GEO) may be a synonym for geosynchronous equatorial orbit,[10] or geostationary Earth orbit.[11]
The first geosynchronous satellite was designed by
Conventional wisdom at the time was that it would require too much
By 1961, Rosen and his team had produced a cylindrical prototype with a diameter of 76 centimetres (30 in), height of 38 centimetres (15 in), weighing 11.3 kilograms (25 lb); it was light, and small, enough to be placed into orbit by then-available rocketry, was
Today there are hundreds of geosynchronous satellites providing remote sensing, navigation and communications.[12][1]
Although most populated land locations on the planet now have terrestrial communications facilities (
Types
Geostationary orbit
A geostationary equatorial orbit (GEO) is a circular geosynchronous orbit in the plane of the Earth's equator with a radius of approximately 42,164 km (26,199 mi) (measured from the center of the Earth).
A perfectly stable geostationary orbit is an ideal that can only be approximated. In practice the satellite drifts out of this orbit because of perturbations such as the solar wind, radiation pressure, variations in the Earth's gravitational field, and the gravitational effect of the Moon and Sun, and thrusters are used to maintain the orbit in a process known as station-keeping.[21]: 156
Eventually, without the use of thrusters, the orbit will become inclined, oscillating between 0° and 15° every 55 years. At the end of the satellite's lifetime, when fuel approaches depletion, satellite operators may decide to omit these expensive manoeuvres to correct inclination and only control eccentricity. This prolongs the life-time of the satellite as it consumes less fuel over time, but the satellite can then only be used by ground antennas capable of following the N-S movement.[21]: 156
Geostationary satellites will also tend to drift around one of two stable longitudes of 75° and 255° without station keeping.[21]: 157
Elliptical and inclined geosynchronous orbits
Many objects in geosynchronous orbits have eccentric and/or inclined orbits. Eccentricity makes the orbit elliptical and appear to oscillate E-W in the sky from the viewpoint of a ground station, while inclination tilts the orbit compared to the equator and makes it appear to oscillate N-S from a groundstation. These effects combine to form an analemma (figure-8).[21]: 122
Satellites in elliptical/eccentric orbits must be tracked by steerable ground stations.[21]: 122
Tundra orbit
The Tundra orbit is an eccentric geosynchronous orbit, which allows the satellite to spend most of its time dwelling over one high latitude location. It sits at an inclination of 63.4°, which is a
Quasi-zenith orbit
The
Launch
Geosynchronous satellites are launched to the east into a prograde orbit that matches the rotation rate of the equator. The smallest inclination that a satellite can be launched into is that of the launch site's latitude, so launching the satellite from close to the equator limits the amount of inclination change needed later.[28] Additionally, launching from close to the equator allows the speed of the Earth's rotation to give the satellite a boost. A launch site should have water or deserts to the east, so any failed rockets do not fall on a populated area.[29]
Most
Once in a viable geostationary orbit, spacecraft can change their longitudinal position by adjusting their semi-major axis such that the new period is shorter or longer than a sidereal day, in order to effect an apparent "drift" Eastward or Westward, respectively. Once at the desired longitude, the spacecraft's period is restored to geosynchronous.[31]
Proposed orbits
Statite proposal
A statite is a hypothetical satellite that uses radiation pressure from the Sun against a solar sail to modify its orbit.[32]
It would hold its location over the dark side of the Earth at a latitude of approximately 30 degrees. It would return to the same spot in the sky every 24 hours from an Earth-based viewer's perspective, so be functionally similar to a geosynchronous orbit.[32][33]
Space elevator
A further form of geosynchronous orbit is the theoretical space elevator. When one end is attached to the ground, for altitudes below the geostationary belt the elevator maintains a shorter orbital period than by gravity alone.[34]
Retired satellites
Geosynchronous satellites require some station-keeping in order to remain in position, and once they run out of thruster fuel and are no longer useful they are moved into a higher graveyard orbit. It is not feasible to deorbit geosynchronous satellites, for to do so would take far more fuel than would be used by slightly elevating the orbit; and atmospheric drag is negligible, giving GSOs lifetimes of thousands of years.[35]
The retirement process is becoming increasingly regulated and satellites must have a 90% chance of moving over 200 km above the geostationary belt at end of life.[36]
Space debris
Space debris in geosynchronous orbits typically has a lower collision speed than at LEO since most GSO satellites orbit in the same plane, altitude and speed; however, the presence of satellites in
Debris less than 10 cm in diameter cannot be seen from the Earth, making it difficult to assess their prevalence.[38]
Despite efforts to reduce risk, spacecraft collisions have occurred. The
Properties
A geosynchronous orbit has the following properties:
- Period: 1436 minutes (one sidereal day)
- Semi-major axis: 42,164 km[21]: 121
Period
All geosynchronous orbits have an orbital period equal to exactly one sidereal day.[43] This means that the satellite will return to the same point above the Earth's surface every (sidereal) day, regardless of other orbital properties.[44][21]: 121 This orbital period, T, is directly related to the semi-major axis of the orbit through the formula:
where:
- a is the length of the orbit's semi-major axis
- is the standard gravitational parameter of the central body[21]: 137
Inclination
A geosynchronous orbit can have any inclination.
Satellites commonly have an inclination of zero, ensuring that the orbit remains over the equator at all times, making it stationary with respect to latitude from the point of view of a ground observer (and in the
Another popular inclinations is 63.4° for a Tundra orbit, which ensures that the orbit's
Ground track
In the special case of a geostationary orbit, the
See also
- Geostationary orbit
- Geosynchronous satellite
- Graveyard orbit
- High Earth orbit
- List of orbits
- List of satellites in geosynchronous orbit
- Low Earth orbit
- Medium Earth orbit
- Molniya orbit
- Subsynchronous orbit
- Supersynchronous orbit
- Synchronous orbit
References
- ^ a b c d Howell, Elizabeth. "What Is a Geosynchronous Orbit?". Space.com. Retrieved July 15, 2022.
- ^ Noordung, Hermann (1929). Das Problem der Befahrung des Weltraums: Der Raketen-Motor (PDF). Berlin: Richard Carl Schmidt & Co. pp. 98–100.
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- ^ Wireless World. pp. 305–308. Archived from the original(PDF) on March 18, 2009. Retrieved March 4, 2009.
- ^ Phillips Davis (ed.). "Basics of Space Flight Section 1 Part 5, Geostationary Orbits". NASA. Retrieved August 25, 2019.
- ^ Mills, Mike (August 3, 1997). "Orbit Wars: Arthur C. Clarke and the Global Communications Satellite". The Washington Post Magazine. pp. 12–13. Retrieved August 25, 2019.
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- ^ "Ariane 5 User's Manual Issue 5 Revision 1" (PDF). Ariane Space. July 2011. Archived from the original (PDF) on October 4, 2013. Retrieved July 28, 2013.
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Satellites that seem to be attached to some location on Earth are in Geosynchronous Earth Orbit (GEO)...Satellites headed for GEO first go to an elliptical orbit with an apogee about 23,000 miles. Firing the rocket engines at apogee then makes the orbit round. Geosynchronous orbits are also called geostationary.
- ^ a b c d McClintock, Jack (November 9, 2003). "Communications: Harold Rosen – The Seer of Geostationary Satellites". Discover Magazine. Retrieved August 25, 2019.
- ^ Perkins, Robert (January 31, 2017). Harold Rosen, 1926–2017. Caltech. Retrieved August 25, 2019.
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- ^ "Quasi-Zenith Satellite Orbit (QZO)". Archived from the original on March 9, 2018. Retrieved March 10, 2018.
- ^ a b Farber, Nicholas; Aresini, Andrea; Wauthier, Pascal; Francken, Philippe (September 2007). A general approach to the geostationary transfer orbit mission recovery. 20th International Symposium on Space Flight Dynamics. p. 2.
- ^ "Launching Satellites". EUMETSAT. Archived from the original on December 21, 2019. Retrieved January 26, 2020.
- ^ Davis, Jason (January 17, 2014). "How to get a satellite to geostationary orbit". The Planetary Society. Retrieved October 2, 2019.
- ^ "Repositioning geostationary satellites". Satellite Signals. February 22, 2022. Archived from the original on November 27, 2022. Retrieved May 23, 2023.
- ^ a b US patent 5183225, Forward, Robert, "Statite: Spacecraft That Utilizes Sight Pressure and Method of Use", published February 2, 1993
- ^ "Science: Polar 'satellite' could revolutionise communications". New Scientist. No. 1759. March 9, 1991. Retrieved October 2, 2019.
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Vallado, David A. (2007). Fundamentals of Astrodynamics and Applications. Hawthorne, CA: Microcosm Press. p. 31. OCLC 263448232.
External links
- Satellites currently in Geosynchronous Orbit, list updated daily
- Science@NASA – Geosynchronous Orbit
- NASA – Planetary Orbits
- Science Presse data on Geosynchronous Orbits (including historical data and launch statistics)
- Orbital Mechanics (Rocket and Space Technology)
- NASA Astronomy Picture of the Day: Time lapse of Geostationary Satellites Beyond the Alps (11 April 2012)