Thermal balance test results of SCIAMACHY thermal bus unit

The Thermal Bus Unit (TBU) transports the heat from the eight detector modules of the SCIAMACHY instrument, over a distance of one meter, to the passive radiant cooler. It is supported by Glass Fibre Reinforced Plastic (GFRP) struts and it is equipped with cryogenic heat pipes, trim heaters, low emissivity gold coatings and MLI blankets. The thermal design of the TBU has been verified by analysis with a thermal mathematical model and by breadboard testing (support struts). The flight model of the TBU is subjected to a thermal balance test in the vacuum chamber at Fokker Space B.V. The aim of the test is to verify the required thermal performance of the TBU such as: temperature drops over the main heat flow paths heat leaks via glass fibre suspensions and struts heat leaks via multi layer insulation blankets performance of goldised surfaces sensitivity for trim heating verify the thermal mathematical model of the TBU. The preliminary test results show good perfomance of the TBU with respect to temperatures gradient. Possible retrimming of some washers may even increase the performance. The heatflow from the shroud to the heatpipe is near its worst case expected value and it will be investigated if the performance will still be within requirements with this higher radiative coupling. The measured temperatures show good correlation with the thermal model and give confidence for the in orbit performance of the Thermal Bus Unit.