On-orbit performance of the Hubble Space Telescope optical control system

On-orbit data are used to examine the performance of the Hubble Space Telescope optical control system. The precision, relative accuracy, and absolute accuracy of the off-axis Wavefront-Sensor measurements are evaluated and compared with design requirements. The internal stability of the sensors is better than 0.006 microm rms over five years, including launch. Random errors are estimated to be within 0.01 microm rms. Systematic errors are present in the estimates of focus, spherical, and coma aberrations, but none has been identified for astigmatism. Primary-mirror spherical aberration is believed to be the probable cause of all subspecification performances.