GHRS Instrument Science Report 044 SSA Spiral Search Tests Results for Centering and Throughput 10/92 Ronald L. Gilliland Abstract excerpted from the report: The primary GHRS science aperture is the 0.25 arcsec SSA with a size matched to the spectroscopic resolution element. Because a planned flux peakup capability in the SSA did not work well in SV testing, precise acquisitions to the SSA center have remained a problem. Without a robust means of centering a star in the SSA, throughput measurements have also remained inaccurate. Without an SSA centering algorithm placement in the SSA requires: 1) a precise centering within the LSA, and 2) a precise blind offset to the SSA. Two calibration proposals developed for Cycles 1 and 2 have been used to test positioning to the SSA following A2 acquisitions. We document how a successful PDB update to improve the initial centering in the LSA was derived. Also discussed are determinations of the SSA throughput which with perfect centering is considerably higher than that found during SV. These SSA spiral search tests provide information necessary for simulations of a planned SSA flux peakup capability.
