Rendez-vous in orbit
Given that manoeuvrability in space is limited, the only way for two spacecraft to rendezvous is to approach one another in the same plane, using carefully gauged and directed impulses.
Docking of the Space Shuttle Discovery to the Hubble Space Telescope. Crédits : NASA
The target spacecraft, which may be a satellite or a space station, is usually already in a circular Earth orbit. For the two to be in the same plane, the launch base must be in the plane of the target when the second spacecraft lifts off. To get this coordination right with respect to the Earth’s rotation, the spacecraft must be launched within a window that lasts only a few minutes every day.
The chasing spacecraft is injected into a lower, and therefore faster, circular orbit and has to perform a series of manoeuvres to close the gap. Once both spacecraft are in the same orbit, a further series of operations brings them together at a very low relative speed of about 1 cm/s.
Imagined by Jean-Pierre Penot (CNES) and Bernard Nicolas, illustrated by Bernard Nicolas
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This closely controlled rendezvous technique is used to repair or even retrieve satellites. It also serves to ferry cargo and new elements for space station assembly. |
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