MetOp-SG MicroWave Imager (MWI): Thermal Control System Design, Challenges and Solutions for a Conical Scanning Radiometer Payload

The MicroWave Imager (MWI) instrument is part of the payload complement of the MetOp-SG Satellites. MWI is a conical scanning radiometer with multiple frequency channels covering 18.7 GHz to 183.3 GHz. The instrument rotates at constant speed and collects the microwave radiation from Earth surface and atmosphere. MWI will provide precipitation monitoring as well as sea ice extent information. The microwave radiation from the scene is collected by the antenna reflector and focused to the respective horns. The scene is scanned by rotation of the complete antenna. During each rotation, the platform angular sector where the antenna beam looks at is used to calibrate the receivers. A calibration mirror is used to collect the energy coming from the cold sky. An onboard hot target provides an additional calibration point. These elements constitute the Calibration Assembly. The MWI Thermal Control System (TCS) has to cope with very strict stability and gradients requirements, especially regarding the Calibration Assembly. The TCS’s task is to guarantee the survival and the operational temperature ranges of the equipment and, in addition, to keep the payload in condition to make correct calibrations and measurements. The thermal design and associated model will be presented, focusing on the most critical parts and analyses. The relevant results will then be shown and discussed. Finally, the paper discusses the problems encountered, the solutions adopted and the lessons learned during the design and optimization steps.