The higher an item's controlled operating temperature and the greater the amount of heat it dissipates, the more strongly it will be coupled to a radiative surface. During cold mission phases and in particular when the equipment is not very active, it has to be kept warm by heaters. The flight software manages the thermal control system. Temperature measurements recorded by a network of sensors, are compared to reference values. The heaters are then switched on and controlled strictly according to need.
Some items require very precise temperature control.
This is the case for gyroscopes or the onboard clock, which are controlled to within a tenth or a hundredth of a degree respectively. Measurements of the power consumed by heaters gives a precise indication of the state of the satellite. Temperatures and heater control laws can be changed from the ground. The thermal control system is designed using detailed numerical modeling of the satellite and requires powerful software for calculating energy fluxes and temperatures. Modeling is also based on laboratory testing of materials and partial mock-ups.