Artificial satellites in retrograde orbit
Encyclopedia
Artificial satellites are rarely placed in retrograde orbit. This is partly due to the extra velocity (and fuel) required to go against the direction of the rotation of the Earth.

Most commercial earth observing satellites use retrograde orbitwww.ioccg.org/training/turkey/DrLynch_lectures2.pdf "Most Earth observing satellites are launched so as to have retrograde orbits.". And almost all communication satellites use prograde orbits.

Examples

Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

 has successfully launched five Shavit
Shavit
Shavit is a space launch vehicle produced by Israel to launch small satellites into low earth orbit. It was first launched on September 19, 1988 , making Israel the eighth country to have a space launch capability after the USSR, United States, France, Japan, People's Republic of China, United...

 satellites in retrograde orbit. One or more of these are spy satellites. They were launched in retrograde orbit so that launch debris would land in the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

, and not on Israel's Arab neighbors.

Earth-observing satellites may also be launched into a sun-synchronous orbit
Sun-synchronous orbit
A Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...

, which is slightly retrograde. This is typically done in order to keep a constant surface illumination angle
Illumination angle
The illumination angle is the angle between the inward surface normal and the direction of light. This means that the illumination angle of a certain point of the Earth's surface is zero if the Sun is precisely overhead and that it is 90 degrees at sunset and at sunrise....

, which is useful for observations in the visible or infrared spectrums. SEASAT
Seasat
SEASAT was the first Earth-orbiting satellite designed for remote sensing of the Earth's oceans and had on board the first spaceborne synthetic aperture radar . The mission was designed to demonstrate the feasibility of global satellite monitoring of oceanographic phenomena and to help determine...

 and ERS-1 are examples of satellites launched into sun-synchronous orbit
Sun-synchronous orbit
A Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...

s for this reason.

Space warfare and accidents

Arthur C. Clarke
Arthur C. Clarke
Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...

 wrote an article called, "War and Peace in the Space Age," in which he suggested that an artificial satellite in retrograde orbit could use "a bucket of nails" to destroy an SDI
Strategic Defense Initiative
The Strategic Defense Initiative was proposed by U.S. President Ronald Reagan on March 23, 1983 to use ground and space-based systems to protect the United States from attack by strategic nuclear ballistic missiles. The initiative focused on strategic defense rather than the prior strategic...

 (anti-warhead) satellite. This premise was ridiculed on account of the vastness of space and the low probability of an encounter.

Nevertheless, a satellite in retrograde orbit could pose a major hazard to other satellites, especially if it was placed in the Clarke belt, where geostationary satellites orbit. This risk highlights the fragility of communication satellites and the importance of international cooperation in preventing space collisions due to negligence or malice.

See also

  • Satellite
    Satellite
    In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

  • Shavit
    Shavit
    Shavit is a space launch vehicle produced by Israel to launch small satellites into low earth orbit. It was first launched on September 19, 1988 , making Israel the eighth country to have a space launch capability after the USSR, United States, France, Japan, People's Republic of China, United...

  • Anti-satellite weapon
    Anti-satellite weapon
    Anti-satellite weapons are designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the United States, the former Soviet Union, and the People's Republic of China are known to have developed these weapons. On September 13, 1985, the United States destroyed US...

  • USA 205
    USA 205
    USA-205, also known as Space Tracking and Surveillance System Advanced Technology Risk Reduction , and previously as Block 2010 Spacecraft Risk Reduction is a satellite operated by the United States Missile Defense Agency. It was launched to demonstrate new technology for missile detection early...

    An example of a retrograde satellite

Sources and external links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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