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Prior to successful launch of IRS-1A, two different thermal balance tests were carried out, one on the Structure Thermal Model using heater pad technique and second on Engineering Model, using solar simulation technique. The temperature match was found to be better for extreme cold case in STM test and for EOL case in solar simulation test and not so good for other cases. An attempt was made to find out the reasons for this mismatch, but the exact reason could not be ascertained. The flight temperatures were predicted, based on solar simulation test data, which matches well with on orbit data.

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.