The Supernova / Acceleration Probe: A High-Accuracy Star Guider

The Supernova / Acceleration Probe (SNAP) will acquire photometric and spectroscopic data of approximately 2000 supernovae per year in the 0.35 to 1.7 micron wavelength range. To accomplish this mission, SNAP's attitude control system system must fulfill two functions: pointing each instrument to a supernova to be studied and keeping the focal plane of the instruments stable during the whole acquisition time. The typical 500 second exposures of SNAP require guiding stability better than 0.03 arcseconds at the focal plane. In this poster it is shown that dedicated sensors within the science package can achieve the required sensor accuracy using a small portion of the field of view of the primary telescope. It is shown in particular that it is possible, using star light gathered by the full two meter aperture of SNAP's telescope, to sense pointing drifts to the desired accuracy of 0.03 arcseconds with a single star as faint as magnitude 16 and centroiding calculations in a single 30 millisecond sample over 95 % of the sky. This project is supported in part by the Department of Energy.