A mission configurable modular satellite bus structure composed of several scalable modules, including a propulsion module and one or more stackable space modules, each using standard subsystems or components with common structures and/or interfaces, that can be processed in parallel to minimize nonrecurring and recurring costs. Each stackable space module includes a generally cylindrical central hub having a plurality of radial rib panels extending outwardly therefrom to form a plurality of bays for containing subsystem equipment. The hub includes a hollow center sized to receive the propulsion module as a fully assembled unit. The radial rib panels carry the primary structural load of the spacecraft. Also provided are removable side access panels that form enclosures for the bays. The side access panels include equipment mounts along an inside surface for mounting the subsystem components and radiators along an outside surface to provide thermal cooling for the mounted subsystem equipment. The modular bus structure of the present invention is lightweight, stiff, strong, dimensionally stable and is therefore most suitable for highly agile, remote sensing commercial, civil space and government missions. The high degree of access to the spacecraft interior afforded by the present invention allows the various subsystems to be installed as separate, line tested assemblies.