A multi-use launch system comprises a plurality of different modules releasably securable together into a plurality of different possible launch configurations. The modules include an at least partially expendable, unmanned first stage unit which is capable of single-stage-to-orbit operations on its own carrying internal or external payloads, or as part of a multi-stage-to-orbit system for higher payload capacity launches. The first stage unit is demountably securable to other first stage units, unpowered cargo-carrying units, and/or manned space vehicles. The first stage unit may be completely expendable after launch.