A satellite consists of various sub-systems such as structures, motion mechanisms, temperature control system, electrical power supply and satellite propulsion. One of these sub-systems is satellite thermal control, which plays a very important role in satellite operation. The task of the thermal control system is basically to ensure that all parts of the satellite and its equipments are maintained in an allowable range of temperature. Thermal control in these systems is carried out in two ways: active and passive. In passive ways, thermal condition of an equipment is controlled using passive elements such as paint, insulation, and heat exchanger; while in active methods, closed loop systems with suitable temperature feedback along with a thermal actuator are used. In this study, the design of an active thermal control system is carried out for one of the satellite equipments for testing in a ground testbed. These highly sensitive and expensive electrical equipments are first tested on ground testbeds, prior to being placed on the satellite. Similar to their real operation, their temperatures have to be controlled in allowable range during the ground tests. The design of the controller, requires the dynamic equations of the system, which can be obtained using the energy conservation equations. In this study, the dynamic equations of the system are obtained using lumped parameter method. The system behavior under different thermal loads are simulated in two different software, including MATLAB and SINDA (SINDA / FLUINT), and their results are verified. The inlet water temperature to the heat exchanger of the testbed is the control input to the system. Two different controllers are designed for this system, including fuzzy rule based controller and model based robust adaptive controllers, and their results are compared. The fuzzy controller is a supervisory controller which adapts the PID controller coefficients. In robust adaptive controller, the thermal system parameters are considered unknown, and the controller in designed in a way to ensure the stability of the system using Lyaponove method. Under similar thermal load, the robust adaptive controller maintains the temperature of the system in the allowable range more satisfactory than the fuzzy supervisory contoller. Keywords: Thermal control subsystem, Lumped parameters method, Fuzzy-PID controller, Robust-adaptive controller
