The Thermal Testing of Euclid STM

Euclid (named after the ancient Greek mathematician Euclid of Alexandria, the “father of geometry”) is a medium-class mission in ESA's Cosmic Vision programme to investigate the expansion of our Universe over the past ten billion years. ESA has selected Thales Alenia Space as the Prime Contractor, with the overall responsibility for the building of the satellite, and Airbus Defence and Space Toulouse as Sub Contractor, with the responsibility to design and build the payload module. The thermal balance test of the spacecraft STM was held in August 2019 at the Cannes facility of Thales Alenia Space. The satellite will be launched by a Soyuz to the L2 Sun-Earth Lagrange point in 2022. The most critical aspect of the thermal design is the necessity to minimize the effect of variations of the thermal environment on the temperature of the payload module baseplate and consequently on the instruments performance. For this reason the purpose of the thermal balance test held in Cannes was specifically designed in order to verify, besides the general performance of the thermal control system, the dynamic behavior of the telescope elements and above all the model accuracy in predicting the temperature variation of the PLM baseplate as a response to changes in the PLM external environment. The environment changes have been implemented, mainly, by using the solar IR simulator heated plates routinely used in the test to simulate Sun heating. Given that it was not possible to perfectly reproduce the actual flight variations of thermal environment due to limitations in the test setup, a complex task of model correlation was necessary to bridge the gap between the test transient and the actual mission conditions. This paper reports on the test activity and on the correlation subsequently performed, with a particular focus on the thermal stability aspects.