The ASPIICS solar coronagraph aboard the Proba-3 formation flying mission Scientific objectives and instrument design

We describe the scientific objectives and instrument design of the ASPIICS coronagraph aboard the Proba-3 mission of the European Space Agency launched on 5 December 2024. Proba-3 consists of two spacecraft in a highly elliptical orbit around the Earth. One spacecraft carries the telescope, and the external occulter is mounted on the second spacecraft. The two spacecraft fly in a precise formation during 6 hours of a 19.63 hour orbit, together forming a giant solar coronagraph called ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun). The very long distance between the external occulter and the telescope (around 144 m) represents an increase of two orders of magnitude compared to classical externally occulted solar coronagraphs. This allows the inner corona to be observed in eclipse-like conditions, i.e., close to the solar limb (down to 1.099 R-circle dot) and with very little stray light. ASPIICS provides a new perspective on the inner solar corona that will help solve several outstanding problems in solar physics, such as the origin of the slow solar wind and the physical mechanism of coronal mass ejections.