Envisat In-Orbit Thermal Performance – A Validation of the Advanced Testing Technique 2003-01-2584

Envisat is the largest and most ambitious earth observation spacecraft in the history of European space exploration. The Envisat spacecraft is funded by the European Space Agency, ESA, and was designed and built by Astrium. It carries a unique combination of instruments and sensors to make scientific measurements of our planet. Among the wide range of information being gathered, Envisat is looking at clouds, atmospheric temperature and composition, land temperature and topography, vegetation, flooding and fires, sea temperature and currents, global circulation, pollution and traffic, sea ice mapping and movement. Its total range of capabilities represents a significant advance over the previous generation of Earth observation spacecraft.

Envisat was launched on an Ariane 5 launch vehicle on March 1st 2002, and flies in a sun-synchronous near polar obit at an inclination of 98° and an altitude of 800km, providing an orbital period of 101 minutes with a repeat cycle of 35 days. Global coverage is achieved in one to three days due to the wide field of view of the instruments. The satellite is 10m tall in its stowed configuration (25m when fully deployed), and weighed in at over 8 tonnes at launch.

This paper discusses the in-orbit thermal performance of the thermal control system and compares it with the pre-launch predictions. The thermal mathematical model used for the pre-launch predictions was correlated against the results from the thermal balance testing. While the Service Module was tested using a traditional method, the PLM was tested using an advanced infrared testing technique. The ultimate validation of this testing technique is the comparison between the pre-launch predicted and in-orbit performance. This comparison shows a very good correlation between the predicted and in-orbit thermal performance. As a consequence, the advanced testing technique used, for the PLM, on the Envisat programme is fully validated