The SIde-Looking Coronagraph for the solar orbiter mission: Optical and mechanical designs

The SIde-Looking Coronagraph (SILC) is intented to be proposed as part of the payload of the Solar Orbiter mission of the European Space Agency. Solar Orbiter will follow elliptic orbits with a large range of heliocentric distance, from 0.21 to 0.6 AU, and will reach heliographic latitudes as high as 38°. Furthermore, the spacecraft will have an offset pointing capability so as to target any point of the solar disk. These characteristics, in addition to the severe thermal environment, are very restrictive for a coronagraph and lead us to propose an externally occulted coronagraph entirely protected from direct sunlight by remaining in the shadow of the spacecraft and looking sideways. The optical design follows the general principles of an externally occulted coronagraph adapted to the side-looking concept. Although SILC loses the full spatial coverage of the corona, it can observe the inner part of the corona (down to 1.5 solar radii) during the whole mission and compensate the off-pointing of the spacecraft. The optical and mechanical designs of SILC are presented in detail.