Abstract: Spacecraft structures which are suitable for mounting within the bay of a space shuttle. Each structure comprises a plurality of modules, each module in the form of a truss network, these networks being secured to one another. Electronic payloads, thrusters, fuel tanks, solar arrays and other equipment are attached to the trusses. The end modules of each spacecraft structure include adjustable trunnions to releasably secure the spacecraft structure to the shuttle. A module may include a keel for releasably securing it (and the spacecraft structure of which it is a part) to the shuttle. Each spacecraft structure may be individually designed. For example, the number of expansion modules secured between two end modules of a structure may be varied as required by the load carrying capacity desired of a spacecraft structure.