Orbital Station-keeping - Station-keeping in Low-earth Orbit

Station-keeping in Low-earth Orbit

For a spacecraft in a very low orbit the atmospheric drag is sufficiently strong to cause a re-entry before the intended end of mission if orbit raising manoeuvres are not executed from time to time. A typical example of this is the International Space Station which has an operational altitude above Earth surface of 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 re-entry of the station, it is from time to time being re-boosted to a higher orbit. The chosen orbital altitude is a trade-off between the delta-v needed to counter-act the air drag 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. On 25 April 2008, the Automated Transfer Vehicle "Jules Verne" raised the orbit of the ISS for the first time, thereby proving its ability to replace (and outperform) the Soyuz at this task.