In-Orbit Experience with Sciamachy Active Thermal Control Systems 2003-01-2470

Sciamachy is a Dutch/German Earth Observation Instrument on board of the European Envisat satellite, which was launched on March 1^st 2002. The goal of the instrument is to observe concentrations of multiple trace gases in the upper atmosphere. Due to the character of the instrument special thermal control methods have been incorporated in the instrument design. Amongst these are the active thermal control loops for the detector modules and the optical bench module. The 8 detector modules, which are cooled with a passive cooler to circa 150 - 240 K, are stabilized with three heaters that are controlled via telemetry. The optical bench module is provided with three feedback-controlled heater loops. This paper focusses on the in-orbit thermal observations, the correlation with the thermal predictions, the fine-tuning of the parameters in the active thermal control systems, and the important role of the thermal control heater system in the solution of problems with outgassing-induced ice layers on the coldest detectors.

The temperature result of channels 1-6 shows very good comparison with the predictions. The temperature level and stability is within requirements. The trimheater power available seems enough to keep the temperatures stable throughout its lifetime. More definite conclusions can be made after one whole season, when degradation results are possible to deduct more accurately. The result until now however indicate a first year degradation < 1 K.

The predicted sensitivities, with one correction, correlate well with the observed temperature changes.

The temperatures of channels 7 & 8 are able to stay below the required 150 K limit. However a clear contamination effect from within the detector module still can be observed. After a number of decontamination loops it is clear that improvements are made.