Helmut Kreeb

The thermal control system of the German direct transmitting communication satellite TV-SAT

launcher. The spacecraft is foreseen for 3 simultaneously operating channels with a The German TV-SAT belongs to the new gelifetime of 5 years of operation. The deneration of direct transmitting communisign is carried out according to the follocation satellites, which consumes some wing system requirements: kilowatts of electrical power and therefore produces severe thermal problems concerning heat rejection and temperature stabilisation. Heat pipe technology must be introduced to overcome the thermal.difficulties. The main heat dissipators on the payload module are the travelling wave tubes (TWT) , the electrical power converters (EPC) and the output-multiplexer (OMUX) which is located on the earth panel. Three TWTts and three EPCs are placed at the north panel, two TWTts and two EPCts are placed on the south panel of the A3 satellite version which is under detailed development since July 79. In the worst case, all TWTs and EPCts are active at one panel and no dissipation is produced on the opposite panel. This requirement demands for a thermal connection between both panels which is performed by means of heat pipes which connect the north with the south panel via the OMUX. The OMUX heat dissipation therefore can be transferred either to the northor the south panel whichever is colder; also a heat flux from the hotter to the colder panel can take place. Beside this, the temperature of the OMUX can be held within the required small range without any other thermal control mechanism. For the satellite bus, the service module and the propulsion module, a conventional passive thermal control system assisted by heaters is foreseen. The highlights in this area are the thermal design of the batteries and the shunts which both need separate individually designed radiators for heat rejection.