In astrodynamics orbital stationkeeping is a term used to describe a particular set of orbital maneuvers used to keep a spacecraft in assigned orbit, either low earth orbit (LEO), or geostationary orbit (GEO). It is especially important for satellite communications systems since maintaining proper satellite position over long periods of time is crucial for the operation of those systems. Astrodynamics is the study of the motion of rockets, missiles, and space vehicles, as determined from Sir Isaac Newtons laws of motion and his law of universal gravitation. ... An orbital maneuver is a change from one orbit to another, accomplished by applying thrust. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... A low Earth orbit (LEO) is an orbit in which objects such as satellites are below intermediate circular orbit (ICO) and far below geostationary orbit, but typically around 350 - 1400 km above the Earths surface. ... A geostationary orbit (abbreviated GEO) is a circular orbit directly above the Earths equator (0º latitude). ... U.S. military MILSTAR communications satellite A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications using radio at microwave frequencies. ...

Stationkeeping maneuvers require inclusion of a particular delta-v in the mission's delta-v budget. Due to its usually low requirements for propulsive impulses the stationkeeping is usually performed using attitude control system's thrusters. General In general physics delta-v is simply the change in velocity. ... Delta-v budget (or velocity change budget) is a term used in astrodynamics and aerospace industry for velocity change (or delta-v) requirements for the various propulsive tasks and orbital maneuvers over phases of the space mission. ... In the context of spacecraft, attitude control is control of the angular position and rotation of the spacecraft, either relative to the object that it is orbiting, or relative to the celestial sphere. ...

Stationkeeping is particularly hard for spin-stabilized satellites.

Stationkeeping in LEO

Stationkeeping is necessary for some objects such as the International Space Station or the Mir or Salyut stations. The International Space Station has an operational altitude above Earth between 330 and 410 km. Due to atmospheric drag, the space station is constantly losing orbital energy. In order to compensate for this loss, which would eventually lead to a reentry of the station (time depends on solar activity), it is being reboosted to a higher orbit from time to time. The chosen orbital altitude is a trade-off between the delta-v needed to reboost the station and the delta-v needed to send payloads and people to the station. The upper limitation of orbit altitude is due to the constraints imposed by the Soyuz spacecraft. ISS Statistics Crew: 2 As of August 21, 2005 Perigee: 352. ... MIR is a TLA that could mean: Mail-in rebate Medical Inspection Room - the place for sick parade in most British and Commonwealth militaries and many NGOs. ... The Salyut (Russian: Салют, Salute or Firework) program was a series of space stations launched by the Soviet Union in the 1970s. ... Earth, also known as Terra, and Tellus mostly in the 19th century, is the third-closest planet to the Sun. ... Atmospheric drag is a form of drag, which is the force that opposes an object moving through a liquid or gas. ... General In general physics delta-v is simply the change in velocity. ... Soyuz TMA-6 spacecraft approaching International Space Station Soyuz 19 spacecraft as seen from Apollo CM Soyuz spacecraft of the Apollo Soyuz Test Project (ASTP) Early 7K-OK Soyuz at National Space Centre, Leicester, England Soyuz (Soyus, Союз, union) is a series of spacecraft designed by Sergey Korolev for the Soviet...

Stationkeeping in GEO

Due to luni-solar perturbations and the ellipticity of the Earth equator, an object placed in a GEO without any stationkeeping would not stay there. It would start building up inclination at an initial rate of about 0.85 degrees per year. After 26.5 years the object would have an inclination of 15 degrees, decreasing back to zero after another 26.5 years. Therefore, a lot of energy has to be devoted to maneuvers that compensate this tendency. This part of the GEO stationkeeping is called North-South control. The ellipticity of the Earth equator is causing an East-West drift if the satellite is not placed in one of the stable (75 degrees longitude east, 105 degrees longitude west) or unstable (15 degrees longitude west, 165 degrees longitude east) equilibrium points. Nevertheless, this part of GEO stationkeeping, called East-West control requires significantly less amount of fuel than North-South control. Therefore, in some cases aging satellites are only East-West controlled. This would still guarantee that the satellite is always visible to a steerable antenna. Earth, also known as Terra, and Tellus mostly in the 19th century, is the third-closest planet to the Sun. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... Earth, also known as Terra, and Tellus mostly in the 19th century, is the third-closest planet to the Sun. ...

Taking into consideration the relatively long periods of operation of modern GEO satellites (up to 15 years) the delta-v expended over such a period can be substantial (about 46 m/s per year). It is therefore crucial for GEO satellites to have the most fuel-efficient propulsion system. Some modern satellites are therefore employing a high specific impulse system like plasma or ion thrusters. A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to provide delta-v. ... The specific impulse (commonly abbreviated Isp) of a propulsion system is the impulse (change in momentum) per unit of propellant. ... An ion engine test An ion thruster, one of several types of spacecraft propulsion, uses beams of ions for propulsion. ...

See also

• Orbital maneuver
• Delta-v budget