Major cost reductions in planetary missions, especially those with high launch energy requirements, are made possible by a modified launch mode in which part of the total launch energy is generated by onboard propulsion rather than by the launch vehicle. Spacecraft separation from the launch vehicle occurs at or near the point of reaching escape velocity. The net effect is a large increase in net payload mass, since the dry mass of the launch vehicle upper stage does not get accelerated to the same final velocity. In missions that require large deep-space maneuvers en route or at destination the modified launch mode is particularly attractive since the spacecraft has to carry an onboard propulsion system, anyway.
The paper describes this launch technique in some detail and examines the various cost saving categories it offers. These include selecting a smaller, less costly launch vehicle for the mission, given a specific payload mass; increasing the payload mass if desired; avoiding complex and time consuming detours for planetary gravity assist purposes to increase payload capability; and avoiding costly miniaturization of design elements. The paper compares the different mission and system requirements associated with the conventional and the modified launch mode, discusses the inherent cost differences and indicates relevant implementation factors.
Meissinger, H., and Simon Dawsom. 1998. “Reducing Planetary Mission Cost by a Modified Launch Mode,” Proceedings of the 3rd IAA International Conference on Low-Cost Planetary Missions.