Abstract: A transfer vehicle for use in a system for transferring payloads from an earth-launch vehicle in one space trajectory to another space trajectory. The system includes a space launch vehicle (FIG. 9) with primary propulsion and guidance systems, a transfer vehicle (FIG. 1) carrying a payload which is stowed in the cargo bay during earth-launch and insertion of the earth-launch vehicle into low-earth transfer trajectory. An engine module (FIG. 3) carrie on-board mission equipment, rocket engine, related fuel supply, guidance equipment, attitude control equipment and electrical power supply equipment (FIGS. 11-20). A grapple system on the earth-launch vehicle (FIG. 9) deploys the transfer vehicle and cargo and restows it for on-orbit repair/modification for earth-return. The transfer vehicle may be multi-staged (FIG. 21) and may be provided with multiple engines (FIG. 23).