Proba-3’s formation flying capability will be further demonstrated by the quality of its scientific results, following the tradition of ESA’s Proba microsatellite family. The twin satellites will form a so-called ‘external’ coronagraph, with the coronagraph satellite’s imager shielded from glaring sunlight by the Occulter satellite’s occulting disk – forming an artificial eclipse in space.

The Sun is a million times brighter than its surrounding corona, so eclipsing it is essential for coronal studies. This giant coronagraph system will enrich the solar science with unprecedented study of the close corona. Previous Sun-observing missions such as SOHO incorporate ‘internal’ coronagraphs to study the corona. But their effectiveness is limited by a phenomenon called diffraction, where stray light overspills the edge of the occulting disk.

Progress on this front requires moving the Occulter much further away while still preserving eclipse-like conditions for long periods of time – precisely the performance offered by the Proba-3 external coronagraph. The technique has previously been attempted during the 1975 manned Apollo-Soyuz mission, when an Apollo Command Module blocked light falling on a Soyuz spacecraft.

SOHO uses an internal occulting disk

Proba-3’s two-satellite instrument offers valuable scientific return, targeting an increase in our close-up view of the Sun and its corona from three solar radii down to just 1.08 solar radii as a goal. Although solar physics missions have probed the corona at various temperatures and heights, the region within three solar radii where the solar wind and coronal mass ejections are born remains extremely difficult to observe with sufficient spatial resolution and sensitivity to understand these phenomena.

The mission's implementation phase (Phase C/D/E1) began in July 2014.