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The Envisat spacecraft has a launch mass greater than 8.0 tonnes and external dimensions of 10.0 metres x 2.8 metres x 2.1 metres. Due to it’s large size, it was necessary to perform the thermal balance and thermal vacuum testing in two stages. Firstly, there was the testing of the Service Module and, secondly, the testing of the Payload Module (PLM). This paper discusses the thermal balance testing of the PLM. The PLM, itself, is 7.5 metres tall; too large to fit into a test facility solar beam. Originally, it was intended to conduct two solar beam tests; one for the upper part and the second for the lower part. Following a revision and re-scheduling within the programme, it was decided to perform a single, non-solar beam, thermal balance test. The thermal balance test would be performed using test specific, electrical, heaters and test facility shroud control.

The ROSETTA mission is a European Space Agency spacecraft which will rendezvous with the comet Wirtanen. The spacecraft will deploy a Surface Science Package (SSP) to land on the comet. The spacecraft will continue to orbit the comet for the following 2 years, which will allow other experiments to be performed to study the evolution of the comet processes as a function of heliocentric distance. The spacecraft will use planetary gravity assists to gain enough energy for a rendezvous with the comet. The spacecraft will be at distances ranging from 0.9 Astronomical Units (AU) to 5.25 AU, with long periods of hibernation. The power for the mission is supplied by two Solar Arrays. This means that the available power at 5.25 AU is 3.6% of that at 1.0 AU. Thus, the heater power demand at 5.25 AU has to be low, when the spacecraft is in Deep Space Hibernation mode. Prior to the comet rendezvous, the spacecraft is woken up.