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.
Read more about this topic: Orbital Station-keeping
Famous quotes containing the word orbit:
“The Fitchburg Railroad touches the pond about a hundred rods south of where I dwell. I usually go to the village along its causeway, and am, as it were, related to society by this link. The men on the freight trains, who go over the whole length of the road, bow to me as to an old acquaintance, they pass me so often, and apparently they take me for an employee; and so I am. I too would fain be a track-repairer somewhere in the orbit of the earth.”
—Henry David Thoreau (1817–1862)