A little boost

Although the atmosphere is quite thin at satellite altitudes (Hubble sits in an orbit about 600 km above the Earth), it is not a perfect vacuum. Over time, all Low Earth Orbiting (LEO) satellites feel the effects of atmospheric drag and lose altitude. If the altitude is not restored, the satellite will eventually re-enter (deorbit).

Hubble has no on-board propulsion, so the only way to restore lost altitude is by the creative use of Shuttle jets during servicing missions. Hubble's altitude was increased before the last spacewalk during SM3B, as it was done during both SM1 and SM2.

 Graph showing how Hubble was re-boosted twice during the first and second Servicing Missions. The top of the graph corresponds to 615 km, the bottom to 580. The first re-boost in 1993 was 8 km and the second re-boost in 1997 was 15 km.


Graph showing how Hubble was re-boosted twice during the first and second Servicing Missions. The top of the graph corresponds to 615 km, the bottom to 580. The first re-boost in 1993 was 8 km and the second re-boost in 1997 was 15 km.