9 .13 its tasks, it retrofires and reenters with the reusable components of one DOL. The OTV, with a full payload consisting of four orbiter payloads, and full propellant tanks from four DOL's, is then ready for the orbit-to-orbit transport mission (see Figure 9.4). Confirmation of OTV design allows a corrected calculation of vehicle masses, since the exact value of M, can now be determined. Four fuel and four oxidizer tanks comprise OTV tankage, and the use of commonality masses listed earlier gives a total value of M, equal to 2760 kg. This allows calculation of outbound payload mass, found equal to 261.8 metric tons,inbound propellant mass, 31.2 tons, _and total tank structural mass of 11.3 tons. This corresponds to a tank mass of 3.2 metric tons per DOL flight. This results in an OTV gross weight in earth orbit of 431.8 tons, as summarized in Table 9.2. The primary OTV mission of payload delivery to LS or lunar orbit justifies its design for that case, yet the OTV must provide transportation for work crews in both directions. Since the spa~e shuttle is the only man-rated earth launch system, work crews are launched into low earth orbit in a personnel transport module, pictured in Figure 9.5. Use of NASA design criteria foi the Manned Orbital Facility indicates the necessary allowance of 5.67 cubic meters (200 cubic feet) per man,which sets the occupancy limit of the personnel module at 50,with a minor . safety factor. In order to maintain 1no% load factors, it is assumed that high density crew provisions and other payload is carried in the personnel transport module to bring it to full launch mass of 27.5 metric tons. In a manner similar to that used for the primary mission, it can be calculated that the secondary personnel transfer mission can be accomplished with one personnel transport module and one space shuttle cargo load as outbound payload, and one loaded personnel transport module as inbound payload. The two remaining cargo retention berths are filled on the outbound flight with propellant tanks orbited by the space shuttle. Therefore, the price of the sipgle 27.5 ton inbound payload is the use of half of the outbound payload capability for supplemental propellant. This secondary OTV configuration is shown in Figure 9.5.
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