PROBA-3

PROBA-3 is an ESA formation flying demonstration consisting of two spacecraft - the Coronagraph Spacecraft and the Occulter Spacecraft. Flying in precise formation at a separation of about 150 metres, the Occulter casts a shadow onto the Coronagraph's telescope, creating an artificial eclipse that allows continuous observation of the solar corona as close as 1.1 solar radii - a view otherwise only available during natural total eclipses.

The two spacecraft were placed into a highly elliptical orbit of 600 km × 60,524 km. Formation flying operations occur near apogee, where atmospheric drag and gravitational gradients are low enough to sustain millimetre-level positioning accuracy for up to six hours per pass.