New perspective in solar coronal physics: Giant externally occulted coronagraphs using satellites in flight formation

Formation flying opens new perspectives in solar physics, and allow to conceive giant, externally occulted coronagraphs using a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at a distance of 100 m. ASPIICS (Association de Satellites Pour l’Imagerie et l’Interférométrie de la Couronne Solaire) is a mission proposed to ESA in the framework of its PROBA-3 demonstration program of formation flying which is presently in phase A. ASPIICS is a single coronagraph which will perform both high spatial resolution imaging of the solar corona as well as two-dimensional spectroscopy of several emission lines from the coronal base out to 3R⊙3R⊙ using an étalon   Fabry–Pérot interferometer. The classical design of an externally occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.01R⊙0.01R⊙ from the solar limb. By tuning the position of the occulter spacecraft, it will even be possible to reach the chromosphere and the upper part of the spicules.