While the lower stages of a multi-stage rocket vehicle are discarded before the machine leaves the atmosphere, the upper stages and the spacecraft they carry, if there is a distinction, need to operate in space. Such “space vehicles” generally need “restart-able” rocket engines that can be turned on or off, which is a somewhat...
The US space shuttle’s orbital propulsion system uses storables, and when the orbiter lands a crew in protective clothing has to go out and “safe” it before anyone else is allowed to get near. The nasty behaviour of storables means higher cost, and they are also now generally regarded as environmentally unacceptable and avoided...