75 passengers. The overall configuration and vehicle characteristics are shown in figure 30. The passenger module is illustrated in figure 30 al so. The booster employs four O2/CH4 engines similar to those on the HLLV booster. A series burn ascent mode is utilized and the external tank (ET) is a resized, smaller version of the space shuttle tank, carrying 546 metric tons of propellant versus 715 metric tons for the current STS. Personnel Orbital Transfer Vehicle (POTV) - The functions of the POTV are to deliver personnel and priority cargo from LEO to GEO and to return personnel from GEO to LEO. The reference vehicle is a two-stage (common stage) LO2/LH2 configuration as illustrated in figure 31. The start burn weight is 890 tons withan up payload of 151 tons and a down payload of 55 tons. The up payload consists of 160 personnel in a passenger module, 480 man-months of consumables in a resupply module, and a flight control module piloted by a crew of two. The down payload is identical except the resupply module returns empty to LEO. Cargo Orbital Transfer Vehicle (COTV) - The function of the COTV is to deliver SPS cargo to GEO from the LEO staging area. The basic concept involves the construction of a fleet of reusable electric powered round trip vehicles and their dedicated solar array in LEO. The vehicle uses ion bombardment thrusters with cryogenic argon as the propellant. The ion thruster propellant was selected on the basis of availability, storability, absence of serious environmental impacts, cost, demonstrated performance, and technical suitability. Power conversion options are GaAlAs and Si photovoltaic array systems illustrated in figure 32. The first option utilizes a self-annealing GaAlAs array with a concentration ratio of 2 and provides a LEO-GEO trip time of 133 days and a total round trip time of less than 180 days. Ion bombardment thrusters of 100 cm diameter are used with an Isp of 13,000 seconds and argon as the working fluid. The primary
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