base initiatives are defined by a variety of case studies derived and analyzed by the NASA Office of Exploration [7], These case studies supply a broad spectrum of impacts and requirements on station. In a mimimum impact scenario, station would be utilized solely for the precursory technology and life science research under the assumption that space vehicle assembly, checkout and refurbishment occurs at a separate co-orbiting location. For this case, science missions which require low gravity conditions are not adversely impacted by vehicle processing operations. Conversely, other case studies examine utilization of space station for all low-Earth-orbit support functions including the storage and transfer of liquid oxygen/liquid hydrogen propellant. The accommodation of the propellant management function at Space Station Freedom carries with it a number of issues, including crew safety and station control impacts, and, therefore, requires further analysis to determine the propellant quantities which are feasible for station basing. The identification of requirements for power and other resources for evolutionary space station support of exploration initiatives was based upon the case studies which represent the maximum utilization of station as a transportation node. It was assumed that science missions which require ‘quiet’ conditions coexist with node operations via resource scheduling until vehicle turn-around demand and launch rate prohibit adequate science accommodation. At that time microgravity or vehicle processing operations must ‘branch’ to a separate facility. Potential branching points are the subject of continuing operations analysis at NASA, Langley. R&D Analysis Since the exact evolutionary direction for the SSF is not predictable, several potential R&D evolution scenarios were defined to allow resource requirements to be computed for a broad range of possibilities. These scenarios represent the emphasis of a particular discipline on space station in combination with a particular lift capability to station orbit. Each scenario or utilization emphasis assumes increased resources (primarily lift) will be allocated to the emphasized category be it life science, microgravity research (e.g. crystal growth), commercial production (e.g. commercial production of semiconductor material) or observational sciences (Earth observers/stel- lar viewing payloads). Table I presents the allocation scheme. The utilization category which was designated as the emphasis for the particular analysis received an additional 15% of critical resources beyond that which is listed in Table I. Since the rate and extent to which SSF will grow post-assembly complete will be a function of Earth-to-orbit transportaton support, the analysis of utilization emphases
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