Proba-3 infographic: Formation flying to a fingernail's thickness

To form a stable solar eclipse from the Occulter to the Coronagraph for a planned six hours at a time, the pair has to maintain formation to a precision of a single millimetre, about the same thickness as the average fingernail.

The pair does this autonomously, employing a suite of sensors. Star trackers and satellite navigation are supplemented by inter-satellite radio links, optical cameras tracing LEDs, a laser bounced back via retroreflectors and finally shadow sensors surrounding the ASPIICS aperture.