Passivation

Passivation is the process of removing all stored energy from a spacecraft at end of life to prevent accidental fragmentation. This includes venting residual propellant and pressurant gases, discharging batteries to prevent thermal runaway, and de-spinning reaction wheels. Unpassivated upper stages and dead satellites are the primary source of orbital debris — over 650 fragmentation events have occurred in the space age, many caused by exploding fuel tanks or batteries. International debris mitigation guidelines now require passivation as standard practice.