The personnel orbital transfer vehicle (POTV) uses a single-stage chemical propulsive element (COTV) to transport the crew module and its crew and passengers from LEO to GEO and return (Figure 3). Although significant propellant savings occur with this approach, as compared to a two-stage concept, the percentage of total mass is small when compared with satellite construction mass. However, the major impact is realized in the smaller propulsive stage size and the overall reduction in orbital operations requirements. Individual propellant tanks are indicated for the LO2 and LH2 in this configuration because of uncertainties at this time in attitude controj requirements. With further study, it may be advantageous to provide a common bulkhead tank as in the case of the Saturn S-ll stage and locate the ACS at the mating station of the POTV and personnel module or in the aft engine compartments—space permitting. The POTV utilizes two advanced space engines (ASE), which are similar in operation to the Space Shuttle main engine. The engine is of high performance with a staged combustion cycle capable of idle-mode operation. The engine employs autogeneous pressurization and low inlet NPSH operation. A two-position nozzle is used to minimize packaging length requirements. Since the POTV concept utilizes an on-orbit maintenance/refueling approach, an on-board system capable of identifying/correcting potential subsystem problems to minimize/eliminate on-orbit checkout operations is postulated. The EOTV concept (Figure 4) is based on the same construction principles of the Rockwell reference satellite. The commonality of the structural configuration and construction processes with the satellite design is evident. The structural bay width ot 700 m (solar array width of 650 m) is the same as that of the satellite. The structural bay length is reduced from 800 to 750 m for compatibility with the lower voltage requirement of the EOTV. The solar array voltage must be as high as possible to reduce wiring weight penalties and to provide high thruster performance, yet power loss by current leakage through the surrounding plasma must be minimized. At the proposed LEO staging base, with very large solar arrays and high efficiency cells, an upper voltage limit of 2000 volts is oostulated. These considerations lead to the selection of a two-bay configuration with structural dimensions of 700 mx 1500 m (solar blanket size 650 m x 1400 m) with a total power output of 309 mw (includes 6% line losses). Primary assumptions in EOTV sizing are given in Table 1. The solar array weights are scaled from satellite weights and are summarized in Table 2. Since GaAIAs solar cells are employed in this concept with a concentration ratio of 2 on the solar cell blanket, the resulting cell operating temperature of 125°C allows continuous self-annealing of the solar cells during transit through the Van Allen radiation belt. Figure 3. Personnel Orbital Transfer Vehicle Figure 4. Electric Orbital Transfer Vehicle
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