SEP stage for earth orbital missions

Application of the SEP Stage (SEPS) for earth orbital missions in the Shuttle era has been investigated for the first time. In particular, the geosynchronous payload delivery/retrieval mission was evaluated using SEPS as the upper stage of the Shuttle/Tug system. Results show that SEPS can significantly increase the payload capability of the Shuttle/Tug, especially for the low-technology Tug. The missions can be accomplished using a modified planetary SEPS concept. Use of SEPS can significantly reduce the Shuttle/Tug launches to accomplish projected geosynchronous traffic requirements.