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 tricky problem because under “zero-gee” conditions the propellants do not tend to flow to the bottom of the tanks. To change its orientation, a space vehicle also needs a “thruster” systems, which are small rockets fitted into vehicle to control its roll, pitch (nose up and down), and yaw (nose side to side) orientation, as well as precision acceleration and braking for tasks such as space rendezvous.
In addition, a practical rocket vehicle must contain a number of support systems, such as a radio “command and telemetry” system to allow ground controllers to send commands to the vehicle and receive operating status; sensors and diagnostic systems (telematics) to indicate the vehicle’s health; and a “self-destruct” system to blow the vehicle out of the sky should it suddenly go off course and threaten to fall on a populated area.
