The structural body and primary system of a space vehicle is commonly referred to as a spacecraft bus. The spacecraft bus is used as a transport mechanism for a spacecraft payload much like an ordinary city bus is a transport vehicle for its passengers. Although each spacecraft payload may be quite different from another, all spacecraft buses are similar in their makeup. The spacecraft bus consists of several different subsystems, each with a unique purpose. The structural subsystem consists of the primary structure of the spacecraft, and supports all the spacecraft hardware, including the payload instruments. The structure, which can take various forms depending on the requirements of the particular mission, must be designed to minimize mass and still survive the severe forces exerted on it during launch and on its short trip to space.

The electrical power subsystem provides power for the payload, as well...