Thermal Design of the Fast-On-Orbit Recording of Transient Events (FORTE) Satellite

The FORTE satellite is a collaborative effort between Los Alamos and Sandia National Laboratories. FORTE, which consists of a composite structure, has a total mass of approximately 180 kg. The satellite operates at a nominal circular orbit of 800 km (100 minute orbit period) with a minimum and maximum power dissipation of 13 Watts and 166 Watts, respectively. The FORTE instruments are attached to three decks (nadir, mid, and zenith) which are constructed of aluminum honeycomb with thin graphite facesheets. Body mounted solar panels are located on the outside surfaces of the octagonal shaped spacecraft. The outer surface of the nadir facing deck and two side panels are used as thermal radiators with their outer surfaces coated with white paint. All internal instruments are coated with black paint to enhance thermal radiation to the surrounding environment, and an intervening thermal interlace material is used between the mating surfaces of the instruments and the decks. A thermal model has been developed for the FORTE spacecraft using TRASYS, which calculates the thermal radiation conductances and orbital heat rates (earthshine, direct and reflected solar), and the thermal analyzer SINDA Quasi steady-state temperatures were obtained for both cold (minimum power, beginning-of-life optical properties and heat rates, and noon-midnight orbit) and hot (maximum power, end-of-life properties and heat rates, and dusk-dawn orbit) worst case orbits. Initial temperature results indicated that some of the high power electronics boxes (> 30 Watts) needed to be relocated to the anti-sun side of the spacecraft, and that a thermally passive system was sufficient. In order to provide thermal input to instrument designers, detailed thermal models of the higher power instruments were developed using PATRAN/P-Thermal, COSMOS-M, and PCB-Explorer. The FORTE thermal design will be described and thermal model results presented.