Prediction and test correlation of venting from a satellite enclosure with temperature-dependent outgassing

Abstract

INTRODUCTION The venting analysis of a satellite plays a key role in the planning of thermal vacuum test and mission operations. We have developed a venting simulation model to predict the pressure inside a communication satellite. The predicted pressure is first given in high and low estimates, corresponding to the high and low estimates of the material outgassing rate in the enclosure. The measured data correlate well with these predicted values. Further development of the model, based on a classical rate theory and test data correlation, results in an improved model which produces a single pressure prediction, instead of the high and low estimates. The rate theory assumes an Arrhenius-type relation for the temperaturedependent rate constant. The predicted outgassing rate now varies with both time and temperature. The test data have been used to determine the rate constants in the model. The venting model showed very satisfactory correlation between the predicted pressures and the measured data throughout the test temperature profile. The model is used to predict the pressure responses in the first-cut scenario and the baseline scenario in support of the mission planning. v The ultra high frequency subsystem in a large communication satellite containing high voltage components is subject to damaging corona discharges if the ambient pressure i s higher than some threshold level. The pressure threshold is conservatively set at torr, below which the system is safe from electrical breakdown. Therefore, it is crucial to determine when the interior of the satellite reaches the pressure level so that the subsystems can start operation and when the pressure will remain below the threshold level throughout its mission life at the hottest potential operating temperatures. The pressure inside a spacecraft depends on the material outgassing rate (OGR), which is a function of temperature and exposure time. A venting model for a specific application to the enclosure of a communication satellite was developed (Ref. 1). The outgassing materials in the enclosure can be grouped into four categories; i.e., graphite epoxy laminated panels, Kynar wire insulation, nonmetallic materials, and electronic boxes. The model takes the summation of the outgassing fluxes from each source at the instant as the gas load of the system and computes the pressure. Because of the uncertainties in the OGR, the model computes a high estimate and a low estimate of the gas load, which leads to a high and a low pressure estimate. Further development of the outgassing model using a classical rate theory and correlation of the + Staff Engineer, Senior Member AIAA test data have led to an improved model which ** Staff Engineer, Sr., Member AIAA. gives a single OGR estimate and a corresponding * Staff Engineer pressure prediction. The improved model is used to support the mission planning. Two scenarios of mission operation, corresponding to a baseline nominal profile and a first-cut profile, have been Copyright 01993 by the American institute of Aeronautics and Astronautics, Inc. All rights reserved. L/