Abstract: A spacecraft structure for orbital assembly and servicing includes a payload module, a propulsion module and a bus module each of these modules includes attachement means for separately attching to the cargo bay of the Shuttle directly and via planar cradles. The bus module includes module docking and latching fittings at each end and matching locking and latching fittings at one end of each of said payload and propulsion modules. The bus module includes sectionalized assemblies forming a matrix of identical cavities adapted to receive orbital replacement submodules that allow easy replacement of equipment in orbit by an astronaut.