OTS-2 - Results from thermal tests on a satellite during six years in a geostationary orbit

OTS is a geosynchronous orbit, 3-axis stabilized, European experimental communications satellite, now in orbit for virtually 6 years. Quasi-steady-state thermal tests carried out at all equinoxes and solstices allow observed spacecraft temperatures to be compared with temperature predictions using 'beginning-of-life' thermal coating values. The gradual rise in general temperature due to surface degradation gives continually larger deviations from predictions. The data permits analysis using exponential curves with a least-squares method. Extrapolation then allows prediction of long-term temperatures to be expected; also by comparing equinox and solstice data, the degradation of the optical solar reflector surfaces on both radiators and of the blanket effectiveness may be estimated.