Passivation (spacecraft)

The passivation of a spacecraft is the removal of any internal energy contained in the vehicle at the end of its mission or useful life.^[1] Spent upper stages are generally passivated after their use as launch vehicles is complete, as are satellites when they can no longer be used for their design purpose.

Internally stored energy generally takes the form of unused propellant^[1] and batteries.^[2] In the past, such stored energy has sometimes led to fragmentation or explosion, producing unwanted space debris.^[1][2] This was a fairly common outcome for many of the U.S.^[3] and Soviet rocket designs from the 1960s to the 1980s.^[4] It remains an occasional problem with derelict second stages left in higher Earth orbits; several U.S. rocket stages fragmented in 2018 and 2019.

The International Telecommunication Union (ITU) and United Nations (UN) recommend that satellites in geosynchronous orbit be designed to move themselves to a disposal orbit some 350 kilometres (220 mi) above the GEO belt, and then remove internally stored energy. Most GEO satellites conform to these recommendations, although there are no enforcement mechanisms.^[1]