The observed and measured on-orbit performance of various aspects of the fine guidance sensors is presented and discussed in the light of the original requirements and predictions. The fine guidance sensors are shown to meet or exceed the original requirements concerning dynamic pointing errors, photometric repeatability, and moving-target tracking capability. Calibration accuracy has been sufficient for observations to date, and fine-lock acquisitions are approaching a 100% success rate. Improvements to the fine-guidance-sensor tolerance of telescope spherical aberration, the South Atlantic anomaly, and solar-panel vibrations have been made, and further improvements are expected.
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.
The three Fine Guidance Sensors (FGS's) of the Hubble Space Telescope (HST) have two principal functions: 1) providing an absolute pointing reference to the telescope pointing control system, and 2) serving as an astrometry instrument.
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