Extending the life of satellite on-board units

When units operate on-board of a high capable telecommunication satellite (SC), their life shall expectancy be enhanced. 15-year lifetime, 15kW power, tenths of transponders in С-, Ku-, Ka- and L-bands on-board a spacecraft stipulate the need to develop and to perform a ground development testing on a large amount of thermally stressed on-board units. To be able to reduce on-board units operating temperature ranges it is very important to implement a correct approach in SC thermal control subsystem (TCS) design; an example of main concepts of TCS design for a thermally stressed SC is provided. With the purpose to extend the life of SC on-board units it is necessary to ensure effective conductive paths between the units and the SC panels or SC panels skins where the units are installed. Thermal analyses for on-board units shall be performed considering different modes of units operation, using, for example, a finite-element method, available in COSMOS application of SolidWorks. To ensure long operating life of unit EEE parts used on thermally stressed SC derating of 30…50 % shall be provided. Hot and cold cases of on-board unit baseplate temperatures are being reviewed; the calculation gives the temperatures from minus 10 to plus 40 оС for EEE parts. On-board units’ reliability directly depends on their life expectancy, which, in its turn, depends on the thermal resistance processes occurring within them. A review of theoretical estimation has been provided. The results of the calculations performed for on-board units correlate well with the results of the ground tests and are validated by the results of successful operation of powerful communications satellites such as Express-AM5 and Express-AM6. The paper demonstrates the results of accurate measurements in the temperature range from minus 100 to plus 100 оC done under thermal vacuum for a typical printed circuit board used within an onboard unit designed and manufactured by JSC ISS.