On-orbit servicing

Kurzfassung

You have a flat tire. You will have to buy a new car!" While on earth, nobody would follow such advice; in space, there are few other options than to replace a malfunctioning spacecraft. There are no repair shops and gas stations in the earth orbit. Because of the lack of so-called on-orbit servicing (OOS) opportunities, some malfunctioning spacecraft continue operational work with reduced or hardly any performance. The only general modification, which can currently be undertaken to an arbitrary spacecraft in orbit, is a software update. For example, the bispectral infrared detection (BIRD) satellite [1] started in 2001 with a configuration of four high-precision reaction wheels. Losing one after the other and with only one functional remaining, a significant effort has been made to optimize the attitude-control software with regards to the new constraints. Thus, BIRD is still operational, but other hardware failures, e.g., the inability to deploy solar panels, cannot be compensated by modifying the onboard software. In case of TV-SAT 1 [2], solar panel problems (the fastening bolt for the solar array had accidentally not been removed before launch) prevented the use of the Ku-band transmit antenna and subsequently any TV broadcast service after launch. The satellite had to be moved into a graveyard orbit.