The aim of a good thermal design of a spacecraft or a space experiment is to ensure that the temperatures of the various parts are not extreme and certainly not outside the temperature range over which components such as electronics are meant to operate. In general it is convenient to design things such that the mean temperature is somewhere in the range 10oC to 30oC because this is typical of temperatures on the surface of the Earth and hence temperatures at which equipment operates well and for which experiments have been calibrated. Many spacecraft carry detectors of one sort or another and in general these detectors are best run at a cold temperature in order to minimise the contamination of the detected signal with the unwanted noise of the detector electronics.
What are the thermal requirements of XMM?
In this respect XMM is typical of a space experiment. The main telescope is required to operate at about room temperature whereas the detectors, in this case Charge Coupled Devices CCDs need to operate at about -130oC.
What tools are needed to make a thermal design?A thermal design is achieved by using basic (heat) physics to construct a thermal model of the hardware on a computer and then to "test" how representative the model is by comparing the model with measured temperatures experienced by the hardware when it is put in a thermal vacuum chamber which is designed to represent space as closely as possible. When a good correlation is achieved between the model and the hardware the model can be used as if it were the actual hardware to predict the thermal response of the hardware in different thermal environments.