Lighting test of an instrument onboard Solar Orbiter

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Solar Orbiter is a space mission supported by the European Space Agency (ESA), to which the NASA contributes. It aims to study the properties and dynamics of the heliosphere, this plasma generated by the Sun and that fills the entire solar system. The observation satellite will be launched in 2017 by an Atlas rocket. Onboard, various instruments among which PAS (Proton / Alfa Sensor), designed by a team of IRAP, and which has successfully passed its first lighting test.

Philippe Louarn, researcher at IRAP and responsible for this instrument, explains the principle and the challenge of this illumination test:

To undergo a flow of 13 solar constants (17 kW/m2) and keep its integrity – a test to which the PAS instrument of IRAP has just been subjected – is not it a form of ordaly? This supreme and terrible medieval test – the “judgment of God” – was often a destructive fire test, like grabbing a red-hot iron, to “establish” a judgment or to ensure that one was not going to eliminate a “divine protege”. In our case, it was more pragmatic to verify that the behavior and thermal design of PAS was properly understood and designed… the test of divine benevolence not being imposed by space agencies!

In the hottest phase of the mission, the challenge is to dissipate the 700 W received by PAS, the most “exposed” instrument of Solar Orbiter, by using its single “cold” side, knowing that the temperature in the electronic box must remain below 50°. As Solar Orbiter also spends a considerable amount of time away from the sun, it was also necessary to avoid cooling down too much. 2 to 4W of additional heating had to guarantee a temperature of -40°, at least, while this box was exposed to the 3K of the “deep space”. Did we have the right architecture for our heatshield? Did we choose the right reflective and emissive materials? Did we dimension our radiators correctly ? More generally, did we understand the thermal behaviour of this system?

All this was verified during a continuous ten-day test in mid-October in a special simulation chamber at ESTEC (the “Solar Facility”). This test was the culmination of the development of a particularly sophisticated STM (Structural and Thermal Model) equipped with some 60 temperature sensors. This test, in fact almost a physics experiment, was the result of nearly a year’s work by a team including IRAP (C. Amoros, R. Baruah, S. Bordon, A. Fedorov, C. Garat, E. Lecomte, P. Louarn,R. Mathon, G.Orttner, M.Petiot, P.Rouger, J.Rubiella, H.C.Seran, G.Terrier), the CNES (C.Brysbaert), the companies Epsilon (A.Albert) and MecanoID (D.Zely).

After two intense days of assembly and adjustments, different thermal phases, hot, cold and transient, were tested. Monitoring the temperature evolutions recorded by the 60 sensors, and verifying live the link with the model predictions was the team’s daily routine for one week, days and nights. In the end, all the predicted cases were tested; at 12 solar constants: 350° on the heatshield and ~35° for the electronics, which is rather better than expected in the “hot” case; on the other hand, a little more heating was needed to withstand the sidereal cold (to be confirmed). In the blink of an eye, no miracle and the ordeal might not have succeeded: you can’t resist without help both fire and ice…

In conclusion, a fundamentally successful qualification: the instrument withstands extreme flows and the recorded temperatures are within the ranges predicted by the model. This test campaign will also remain an excellent team memory. Congratulations to all!

IRAP Contact :

  • Philippe Louarn :

Official website of the mission :



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