On Orbit Performance of the Hubble Space Telescope Fine Guidance System Operating in the Coarse Track Mode

Abstract

The Hubble Space Telescope (HST) Fine Guidance System (FGS) was designed and demonstrated to provide a robust Coarse Track capability with a pointing accuracy of .02 arc second rms when tracking a Mv 14.5 star. Orbital data indicates that tracking performance varies from .02 to .065 arc second (Bely and Liu). Two HST hardware characteristics are identified as contributing to the higher than expected pointing errors. High jitter levels are induced by Solar Array Assembly mechanical shocks during and following day/night orbital transitions. Reduced signal to noise performance occurs in the Coarse Track control loop because of the spherically aberrated images from the telescope optics. A Computer simulation has been developed to investigate the operation of the Coarse Track mode performance and to determine if performance can be enhanced by modification of up-link control variables.