Preliminary evaluation of the diffraction behind the PROBA 3/ASPIICS optimized occulter

ROBA-3 is a technological mission of the European Space Agency (ESA), devoted to the in-orbit demon- stration of formation flying (FF) techniques and technologies. ASPIICS is an externally occulted coronagraph approved by ESA as payload in the framework of the PROBA-3 mission and is currently in its C/D phase. FF offers a solution to investigate the solar corona close the solar limb using a two-component space system: The external occulter on one spacecraft and the optical instrument on the other, separated by a large distance and kept in strict alignment. ASPIICS is characterized by an inter-satellite distance of â1/4144 m and an external occulter diameter of 1.42 m. The stray light due to the diffraction by the external occulter edge is always the most critical offender to a coronagraph performance: The designer work is focused on reducing the stray light and carefully evaluating the residuals. In order to match this goal, external occulters are usually characterized by an optimized shape along the optical axis. Part of the stray light evaluation process is based on the diffraction calculation with the optimized occulter and with the whole solar disk as a source. We used the field tracing software VirtualLabTM Fusion by Wyrowski Photonics [1] to simulate the diffraction. As a first approach and in order to evaluate the software, we simulated linear occulters, through as portions of the flight occulter, in order to make a direct comparison with the Phase-A measurements [2].