Thermal Design, Analysis, Testing, and On-Orbit Performance of the INMARSAT 2 Spacecraft

The Inmarsat 2 spacecraft constellation consists of four operating spacecraft, with the first launched in October 1990. The spacecraft thermal design was modelled and validated through an extensive test program, which included solar thermal vacuum tests. Additionally, an on-orbit thermal balance test was performed on the protoflight spacecraft, and the results were compared to thermal model predictions. On-station thermal performance has been excellent, with the exception of the infrared earth sensors, which required design modifications for later flights. Lower than expected solar absorptance degradation has been minimal on the thermal radiators. Evidence of hot soakback from liquid apogee engine firings were observed during transfer orbit. Results of the Inmarsat 2 program demonstrate that detailed modelling and a comprehensive test program will produce a reliable thermal control system.