Figure VI-7.- Cargo orbital transfer vehicle (COTVg) characteristics. The POTV LEO-to-GEO mission is assumed to be initiated at the LEO orbit transfer operation base. Modular OTV elements are docked and propellants tanks topped off. A two-burn injection places the OTV and payload on the synchronous transfer ellipse with a trip time of 8 to 9 hours. At apogee, the circularization maneuver is performed and rendezvous with the GEO SPS construction base is accomplished. GEO orbital stay for a typical mission is between 2 and 7 days. Orbital stay time can be extended for GEO refueling applications. Return to the LEO base is all-propulsive. For the purpose of this study, the conservative choice was made to employ conventional chemical propulsion with all-propulsive return of the vehicle and crew to LEO. Single-stage, 1-1/2 stage (outbound propellant tanks expended), and common-stage configurations are all candidates for this mission. Additionally, for those cases where economic cargo transportation is available, significant advantages may accrue to the POTV by storing propellants in GEO (having previously been delivered by the cargo OTV) for the return journey. A crew module concept layout is shown on figure VI-8. During the operational program phase, the crew module will be used as the manned control compartment for the POTV, now transporting the crew rotation passenger module, which is shown on figure VI-9. High-priority cargo may be carried as POTV payload instead of, or in addition to, the crew rotation passenger module.
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