In some non-nominal operating modes, the spacecraft attitude can deviate, pointing the optical axis towards the sun. After reflection on the optical chain, solar fluxes can be focused onto the detectors, optical windows or other sensitive materials. The solar spot received by the instrument elements is defined by its heat flux density, surface area and the scrolling rate. Materials temperatures can exceed hundreds of degrees in several seconds or few minutes. The objective of the solar illumination test is to confirm that exposed coatings, adhesives or materials in general are able to withstand the short term temperature increase induced by this solar illumination. The testing conditions are derived from the thermal and optical models and from specific project specifications.

A Sun intrusion test setup was developed at ESTEC in order to assess the integrity of materials and sub-assemblies upon extreme temperature increase induced by solar radiation. The optical test setup can be coupled to an UHV vacuum facility equipped with a cryostat and therefore the device under test (DUT) can be cooled down as low as 30K. The light source and optical elements are located outside the vacuum chamber and the light beam can focused onto the device under test with different lenses

A fast speed shutter limits the exposure duration to the sun illumination and allows to “cycle” the device under sun illumination. The optical configuration of the setup allows to tune the power and consequently the heat flux. As it is often difficult to limit down to tens of millimetres the beam spot, aperture masks are used on top of the DUTs.

Sun intrusion test campaigns in the scope of several ESA missions have been conducted in ESTEC laboratories with this setup. The poster will present the test set-up, experimental challenges and results from the testing.