Science

PROBA-3 OSC

Formation-Flying Solar Coronagraph (Occulter Spacecraft) · ESA

The Occulter Spacecraft — the other half of ESA's revolutionary formation-flying solar observatory. This 200 kg satellite carries a 1.4-meter occulting disk that blocks direct sunlight from reaching its partner spacecraft 150 meters away, artificially recreating the conditions of a total solar eclipse for up to six hours at a stretch — roughly 50 times longer than nature ever provides. A laser-based Fine Lateral and Longitudinal Sensor fires between the two spacecraft, measuring their relative position to within a millimeter, while a shadow position sensor uses an onboard algorithm reading light intensity around the coronagraph aperture to keep the Coronagraph spacecraft locked precisely inside the Occulter's shadow. It is, quite literally, one satellite's entire job to cast a shadow on another satellite — with extreme precision, for science.