Two Stage Ballistic, VTOVL - This concept was evaluated in considerable detail by Boeing and JSC. JSC utilized computer aided design techniques (EDIN) to evaluate the following four configurations: Propellant 1st Stage 2nd Stage Payload The characteristics of these vehicles are shown in figure A-16, with a Saturn V for comparison. Weight estimating relationships developed for Saturn were used for sizing and performance and staging points were optimized on the basis of minimum lift-off weight. Both stages retro to a water landing. Boeing developed a concept illustrated in figure A-17. The vehicle was designed for simplicity in construction and operation. It is steered by differential throttling and uses no gimbals. The first stage is landed downrange on water and the second stage on a 5 km diameter pond adjacent to the launch pad. Modified Single Stage to Orbit, VTOHL - This concept was investigated at JSC and utilizes an expendable external hydrogen tank (hence, modified SSTO) and is winged. The vehicle is launched vertically but lands horizontally adjacent to the launch site. Its characteristics and configuration are illustrated in figure A-18. Two Stage Winged, VTOHL - This configuration was analyzed extensively at JSC utilizing EDIN. Seventeen variations representing different engines, propellants, propellant feed arrangements, payloads and structural material were investigated. These variations included: Payload 500 to 1000 K lbs Propellant
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