most cost effective performance. The Future Space Transportation Systems Analysis Study (NAS 9-14323) contracted to Boeing in September 1974, investigated the transportation system concepts best meeting the requirements of several future program scenarios. These studies, plus several in-house heavy lift launch vehicle studies, provided an initial appraisal of candidate vehicle concepts for SPS requirements. The Heavy Lift Launch Vehicle (HLLV) The function of the HLLV is to transport cargo from the earth launch site to LEO. There were five basic vehicle configurations considered: 1. Single Stage to Orbit (SSTO) - Ballistic, VTOVL 2. Two Stage to Orbit - Ballistic - VTOVL 3. Modified SSTO - Winged, VTOHL 4. Two Stage to Orbit - Winged, VTOHL 5. Single Stage to Orbit (SSTO) - Winged, HTOHL Where: VTOVL = Vertical takeoff. Vertical landing VTOHL = Vertical takeoff, Horizontal landing HTOHL = Horizontal takeoff, Horizontal landing SSTO - Ballistic, VTOVL - This concept was investigated extensively by Boeing in the Heavy Lift Launch Vehicle Study and the SPS Systems Definition Study. Its characteristics are shown in figure A-15. The LOX/RP-1 engines are shut down after 127.4 seconds of flight and the LOX/LH^ engines continue alone until a 92.6 x 500 km orbit is achieved. A small separate stage then circularizes the payload's orbit. After discharging the payload, the vehicle is deorbited and reenters. Final deceleration for landing is accomplished by LOX/RP-1 engines which bring the vehicle to near zero velocity. The vehicle retros into a specially constructed 5 km diameter fresh water pond adjacent to the launch site. The vehicle then undergoes refurbishment and is ready for reuse.
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