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The Astrometric Telescope Facility (ATF) is an optical telescope facility of extreme astrometric precision whose principal scientific purpose is the detection and study of planetary systems orbiting nearby stars. The ATF was planned as an initial operational capability (IOC) payload for the Space Station. A change in the Space Station program this year has resulted in a two-phase program. Phase I consists of the original Station's transverse boom with 75 kW of power initially, growing to 125 kW with addition of solar dynamic power, and Phase II adds the upper and lower booms. Only Phase I is currently approved and funded for development. If early operations are important for payloads such as ATF which were originally planned for the upper or lower booms, their suitability for the Phase I Space Station must be evaluated. This paper presents the results of such an evaluation for the ATF. The primary suitability considerations for an ATF Space Station mounting site are mechanical vibration, optical surface contamination (exhaust gases from station-keeping, gaseous and liquid dumping, pressurized module leakage, and particulates), and observable field of view. Specific quantitative environmental data for vibration, exhaust gases, and particulate contamination for the Station are incom-plete. Therefore, the results reported here are preliminary and based upon limited data and some modeled estimates. Only the field of view evaluation was straightforward and based on dimensions from the Space Station Phase B engineering study. Findings from this study show that the Phase I Space Station is marginally acceptable as an ATF platform. The Phase I Station provides an adequate field of view for observations, the vibrational environment is acceptable, and the contamination level during Station quiescent times (without venting) is acceptable. However, the contamination evaluation here is based on partial data and when the contamination levels are fully specified they are expected to exceed ATF's contamination requirements. Therefore, the acceptability of siting the ATF on the Phase I Station will depend upon engineering solutions being found to control the contamination environment. Thus, comparing the Phase I Station to the Phase II Station upper boom for siting ATF, the Phase I Station with higher levels of contamination and vibration levels, is a less desirable platform for ATF. The basic robust design for ATF with minimal design enhancements and with favorable control in the design of the Station, could make the Phase I Station acceptable for ATF operations.
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