In-Flight Results of the Sciamachy Optical Assembly Active Thermal Control System 2004-01-2357
Sciamachy is a Dutch/German Earth Observation Instrument on the European Envisat satellite, which was successfully launched on March 1st, 2002. The goal of the instrument is to observe concentrations of trace gases in the atmosphere.
Due to the required optical accuracy of the instrument special thermal control methods have been incorporated in the instrument design. Amongst these are the active thermal control loops for the optical bench module.
The optical bench module is therefore provided with three feedback-controlled heater loops.
During the commissioning phase, the active thermal control systems in the instrument have been characterised in order to optimise their use during the operational phase of the instrument.
The paper will focus on the thermal design of the optical bench, the control algorithm of the active control system, in-orbit thermal observations of the last 2 years in space, the correlation with the thermal predictions, the fine-tuning of the (temperature) setpoints of the Active Thermal Control system and the lessons learned in this process.
The results show that all OBM control loops show a stability in line with predictions and well within requirements. Also the seasonal variation is in line with predictions. Only the average total power level demanded by the OBM controllers is slightly lower than predicted. However after 2 years in orbit the degradation found is significantly lower that predicted. Therefore, nominal and stable operation of the OBM will be possible for its entire lifetime.