Use of Thermal Analysis for Estimation of Fuel in Propellant Tanks of IRS-1A

The first Indian Remote Sensing Satellite, IRS-1A, has a mono-propellant Reaction Control System(RCS) for orbit and attitude correction. In early phase of spacecraft life some anomaly in fuel mass calculations was observed and one group of tanks were emptied much earlier than expected. This paper explains how heating/cooling rates of propellant tanks and comparison with theoretically calculated temperature response were used for sorting out the anomaly.