9. 9 from low earth orbit to LS or lunar orbit, the primary design is for a maximum outbound payload, MPLO' of 110 tons, and no inbound payload, MPLI' This results in an outbound propellant mass of 264.3 tons, inbound propellant mass of 32.1 tons, and total tank structural mass of 11.7 tons. The total propellant mass for one OTV flight is 296.4 tons, which is very close to the payload capability of four DOL' s . This brings up the subject of cargo containers. Most structural material carried is simply palletized, and very little scar weight is thus encurred. However, propellants launched into orbit must obviously be carried in tanks, which are nonrecoverable due to shuttle download capability being fully utilized for SSME recovery operations. The DOL shroud is similarly nonrecoverable. To minimize expended structure, it is logical to utilize the DOL exclusively as a propellant launch system, with integral propellant tanks which serve as launch protection cover, Earth delivery propellant tanks, and orbital transfer vehicle propellant tanks. This results in the following revised transportation scenario. The basic OTV consists only of the SSME primary propulsion system, avionics,reaction control system, and thrust structure, as in Figure 9.2. Four DOL's are launched,and r~ndezvous with the OTV, having jettisoned only nose and aft skirt aerodynamic fairings. Figure 9.3 shows this configuration designed to retain engine placement and center of mass identical to those of the orbiter. The DOL_ component masses, as compared to those of the orbiter, are compared in Table 9.1. Four space shuttles are launched, which also rendezvous with the OTV. The orbiter payloads are mated to the OTV retention fittings identical to those in the orbiter bay. The now-empty orbiter then separates the avionics, reaction control modules, and SS~E's from a DOL, placing the components into its payload bay,then maneuvers the LOX/LH 2 tank orbited by the DOL into retention fittings on the OTV. The propellant feed lines are connected via fluid transfer quick-disconnect fittings such as the probe-drogue system used in aerial refuelling,or the propellant feed connectors between the shuttle orbiter and its external tank. After each orbiter completes
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