Figure 12-14. Independently powered orbit transfer systems comparison. to GEO are a factor. The trip times for the nuclear electric systems are on the order of several months, whereas the high thrust gaseous core nuclear system trip time is less than 1 day. Economic trades will be required to make a more definitive conclusion on this issue. As discussed in subsection 12. 2.1, the high thrust orbit transfer systems can potentially perform the .dual function of cargo and personnel transfers from LEO to GEO. The use of nuclear systems for personnel transfer will require more extensive studies of the radiation environment where crew modules would be located. 12.2.5 PERSONNEL ORBITAL TRANSFER VEHICLE SYSTEMS Personnel transfer vehicle options included in this discussion are sized for personnel and critical logistics resupply transfers between LEO and GEO. The only propulsive option evaluated is LOX/LH2. All propulsive (all maneuvers of the transfer mission) and aeromaneuvering (aerodynamic braking on the return from GEO) vehicles are described. Figure 12-15 shows a typical configuration for an all propulsive orbit transfer vehicle. From a cost and orbital debris point of view, single and two-stage fully reusable transfer vehicles are preferred over the stage and one-half and two and one-half stage approaches.
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