drive the cargo OTV, removing the necessity of returning this power source to low Earth orbit for reuse and effecting great economies in the overall operation. If, however, bulk cargo and supplies must be delivered to geosynchronous orbit for construction at that location, then an orbit transfer vehicle capable of supplying its own energy for the transfer is necessary. Conventional oxygen/hydrogen chemical propulsion is a candidate for this latter function. The scale of the operation will justify the employment of the highest technology chemical propulsion systems can offer and vehicle arrangements offering the maximum degree of efficiency by use of such stratagems as staging and expending inexpensive components. One candidate system to fulfill this need is a 2-1/2 stage oxygen/hydrogen vehicle. This vehicle is sized to fulfill the requirements of 225 ton payload transferred each trip from low Earth orbit to geosynchronous orbit with dimensions of the payload of 12 m dia. by 12 m in length. The 2-1/2 stage vehicle consists of a lower stage, carrying the greater portion of the propellants, which performs an insertion burn to a near-geosynchronous altitude apogee elliptical orbit. The second stage with the payload separates from the first stage and performs the remainder of the altitude increase to geosynchronous orbit, the circularization burn in geosynchronous orbit and any necessary plane change. The payload and the propellant tanks used by the second stage for its placement burns are separated in geosynchronous orbit and the second stage returned under its own power to low Earth orbit for refueling and reuse. The first stage had earlier performed a circularization burn at the low Earth orbit altitude for rendezvous with the operational support space station in low Earth orbit. The rationale for expending the tanks of the second stage is that the cost of placing the propellants in low orbit which are necessary to achieve the return of the tanks to low Earth orbit exceed the price of replacing them for each mission. This hypothesis may be valid or invalid, depending upon the relative cost of the launch service and fabrication of the propellant tanks which is yet to be determined. 3.4 Personnel Orbit Transfer Vehicle Due to the much smaller payload requirements for transporting personnel, even relatively large numbers of 200 to 500 persons per year, it is assumed that the personnel orbit transfer vehicle is a special purpose device optimized for that function. For an independent chemical propulsion cargo OTV, it may be possible to delete this development and fly the passenger-carrying module as a part of the large chemical OTV outbound cargo. This program cost saving may be assumed whenever the geosynchronous orbit construction location and chemical cargo orbit transfer vehicles are considered. In all other cases, the dedicated personnel orbit transfer vehicle will be required due to the very slow trip made by low thrust cargo OTV's through the Van Allen belt. Information generated by the Future Space Transportation Systems Analysis Study, previous JSC in-house work, and the extensive space tug studies conducted by both NASA and the USAF over the past five years have resulted in a wealth of background information of one candidate concept to achieve this purpose. This concept deploys from the Shuttle operational altitude to
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