Spacecraft thermal testing involves characterizing the performance of the constituent sub-systems as well as integrated satellite at their respective specified acceptance temperature levels. The acceptance level temperatures of the subsystems differ from one subsystem to other within a spacecraft. During the test, the subsystems are maintained at those temperature levels specified by a pre-defined temperature profile using skin bonded heaters and IR lamps. The heaters and IR lamps can be operated using open loop or closed loop control with temperature set point. As the number of heaters to be controlled using open loop increases, it becomes increasingly difficult to maintain the temperatures of the subsystems at their acceptance temperature limits. Closed loop PID control is one of the simplest and reliable means of maintaining the temperature in the dynamic thermal environment inside spacecraft. The paper describes and establishes the closed loop control parameters for IR lamps, skin bonded heaters mounted on low and high thermal inertia systems using Ziegler − Nichols method as the basis. The performance of the controller is evaluated using tuned parameters.