GALILEO HIGH-GAIN ANTENNA DEPLOYMENT ANOMALY THERMAL-ANALYSIS SUPPORT

In April of 1991, the Galileo spacecraft executed a sequence of comman ds to unfurl its umbrella-like high-gain antenna, but confirmation of deployment was not received. The primary theory was that a very high c oefficient of friction existed between the midrib restraint pins and t heir receptacles along the antenna's central tower. Recovery actions i ncluded extreme antenna cold soaking, cyclic warming and cooling of th e antenna, and pulsing the deployment motors to act as a mechanical ha mmer. An analytical model was extensively used to quantify the benefit of these actions. This model was not primarily intended to produce ac curate temperatures in extremely cold environments. Initially, predict ed antenna temperatures for cold soaking were different by as much as 40 degrees C. However, with additional night experience, this differen ce was reduced to within 20 degrees C. Good agreement (within 5 degree s C) with flight data was achieved for antenna warming and meter hamme ring. Although deployment was not achieved, the analytical model evolv ed without extensive revision into an accurate tool for predicting ant enna temperatures.