The propulsion system studies made to select the Attitude Control Propulsion System (ACPS) and Orbit Maneuver System (QMS) for the. McDonnell Douglas - Martin Marietta Space Shuttle Vehicle are summarized in the paper. Both high chamber pressure and low chamber pressure gaseous 02/H2 ACPS concepts are considered in conjunction with ACPS, RL-10, and new development engines for the OMS function. Weights, performance, reliability, maintainability, mission flexibility data are combined with overall system/ vehicle costs to complete the evaluation and the final selection of a high chamber pressure (500 psia) ACPS and liquid pump fed RL-10 OMS
