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An approach to the creation of passive radiative cooling system ensuring temperature levels less than 220K for the optical sensor of scientific space equipment elements is considered. The system is intended for the arbitrary orientation-in-space function under solar radiation. Theoretical analysis of the application field of this system, using heat pipes with constant and variable thermal resistance in a range of solar constant variation (500…2700)W/m2 is given. Experimental results on system models, in which two engaged in parallel thermodiodes with freon-22 and ammonium were used, showed the possibility to attain device temperature levels less than 220 K at the solar constant magnitude 1400 W/m2 and device heat release under (1…2) W.

Microsatellite BIRD (Bispectral InfraRed Detection), mass 92 kg, sizes 550×610×620 mm was put on October 22, 2001 in a sun-synchronous orbit. The passive thermal control system (TCS) provided a temperature range of −10…+30 °C for a payload. It is assembled from precision optical instruments and housekeeping equipment with average power about 35 W. In the observation mode a power consumption peak of 200 W is occurred during 10-20 min. The TCS ensured a thermal stable design of the payload structure and is realised by heat transfer elements (conductors and grooved heat pipes), which thermally connected the satellite segments, two radiators, multilayer insulation and low-conductive stand-offs. Three years in space have brought an enormous volume of telemetric data about thermal performance of the TCS, based on information from temperature sensors, power consumption, attitude relative to Sun and Earth.

For the prediction of the transient behavior of thermal nodes which are interacting within a Thermal Mathematical Model (TMM) it is necessary to know the heat capacity of each node. For instance this is actual for components of opto-electronic devices for space exploration. Other assignment is to define the thermal properties of new structure materials and their combinations. Often the base for the correction of the TMM is the comparison of the calculated node temperatures with the node temperatures measured on a Thermal Engineering Model (TEM) during a Thermal Vacuum Test. The TEM has to be very similar to the flight hardware from the thermal point of view. But very expensive flight components are replaced in the TEM by thermal equivalent dummies. This makes it possible to use all components of the TEM for an unusual but simple experimental determination of their heat capacity as well.