Test plan for the PROBA3/ASPIICS scaled model measurement campaign

PROBA3/ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun) is the first formation flight solar coronagraph, scheduled by ESA for a launch and currently in phase C/D. It is constituted by two spacecraft (one hosting the occulter, diameter 142 cm, and one with the telescope) separated by 144 m, kept in strict alignment by means of complex active and metrology custom systems. The stray light analysis, which is always one the most critical work packages for a solar coronagraph, has been only theoretically investigated so far due to the difficulty of replicating the actual size system in a clean laboratory environment. The light diffracted by the external occulter is the worst offender for the stray light level on the instrument focal plane, thus there is strong interest for scaling at least the occultation system of the coronagraph and test it in front of a solar simulator in order to experimentally validate the expected theoretical performance. The theory for scaling the occulter, the occulter-pupil distance and the source dimension has been developed and a scaled model is being manufactured. A test campaign is going to be conducted at the OPSys facility in Torino in front of a solar simulator (conveniently scaled). This work accounts for the description of the scaled model laboratory set-up and of the test plan.