The ESA Solar Orbiter (SOLO) is an interdisciplinary mission to the Sun. It consists of a single spacecraft, which will orbit the Sun in a moderately elliptical orbit, using a suite of advanced Remote-Sensing and In-Situ instruments to perform a detailed observation of the Sun and surrounding space. Due to the nature of the mission, the spacecraft will get as close as 0.28 AU from the sun, providing the closest ever views of the star, and hence, exposing the different subsystems to very high temperatures. The performance of representative thermal tests under these conditions has been one of the most challenging tasks of the qualification and acceptance test campaigns of the different subsystems, requiring novelty solutions to fulfil the demanding requirements.
SENER is contractor for the delivery of the High Gain Antenna Major Assembly (HGAMA) subsystem. This subsystem is a high-gain dual-axis steerable antenna assembly that provides main uplink and downlink communications between the Solar Orbiter spacecraft and Earth.
When the antenna is deployed it is not protected by the heatshield of the spacecraft and hence it is directly exposed to the sun, having to withstand radiation fluxes of 17,000 Watts per square meter when the satellite reaches the closest point to the star. The intense radiation and high temperatures to which the equipment is exposed has been a technical challenge, not only from design point of view but also for the qualification test campaign. The purpose of the qualification thermal vacuum test was to represent the extreme flight conditions experienced by the antenna using a solar simulator. The levels of solar flux density needed for the test, and the size of the equipment made particularly difficult to find a facility to fulfil the requirements. Some of the most critical points were:
- Test predictions
- Definition of the test thermal cases and set-up
- Location definition and installation of thermocouples
- Infra-Red cameras management during test
- Difficulty of monitoring temperatures above 300ºC
The presentation starts with a brief introduction to the mission, followed by an overview of the subsystem, its components and thermal design main aspects. The content is then focused on the Thermal Balance test and the correlation of the thermal model. To conclude, a list of lessons learned during the test campaign will be presented and discussed.