Design And Implementation Of Cooling System For Focal Plane Assembly Of Astronomical Satellite Camera

The high-performance CCD in an astronomical observation camera is required towork at low temperature-65℃to suppress the dark current. Therefore, the focalplane assembly (FPA) must be cooled independently in order to guarantee itsperformance.In order to satisfy the engineering application requirements of the camera focalplane assembly in space astronomy with good stability, high reliability, small size,light weight and high precision, a cooling control system on a thermoelectric cooler(TEC) was designed in this paper. The80C32microcontroller was used as itssystematic core processor. The data of the real-time temperatures at different points ofthe CCD, captured by the acquiring circuits from the five temperature sensors whichwere mounted at the back surface of the image sensor, were used to be the input of thedigital PID control algorithm. And then the output calculated by the algorithm wasapplied to adjust the control current of the driver circuit of the TEC. Thus the purposeof cooling focal plane assembly was achieved.The importance of high stability and precision cooling to the high-performanceCCD in an astronomical observing camera and the reason why the TEC was used asits cooling component were discussed firstly in this paper. Secondly, the theoreticalbasis, the cooling principle, the working status and the select principle of TEC wereintroduced in detail, and then the cooling module of thermal load was analyzed.Thirdly, the overall design of the hardware control circuit of the cooling system wascompleted and then the decomposed four circuit modules which were temperatureacquiring module, TEC driver module, communication module and calculating andcontrolling module were separately designed in detail. After the schematic circuitdiagram was designed, the PCB of the system was designed according to the principleof component placement and route, and then it was processed and debugged furthermore. Subsequently, the software algorithms of the system were analyzed and developed according to the requirements and boundary conditions of the coolingsystem. And the modularization method was used to finish the outline design of thesoftware whose core algorithm is the digital PID control algorithm. Meanwhile eachmodule of the software was developed in detail, coded and debugged. Finally, theintegration and debugging of the software and hardware of the entire cooling controlsystem were completed.The experimental results of the designed system show that the cooling systemcan realize the temperature gradient of the FPA less than1℃, reach its normaloperating temperature-65℃quickly, and ensure its control precision at±2℃. So itsatisfies the requirements of the focal plane for the astronomical observation camera.