Proba-3 (Project for On-Board Autonomy 3) is the first close formation flying mission for the European Space Agency (ESA). It consists of two independent, three-axis stabilised spacecraft flying 150 meters from one another with the ability to accurately control the attitude and separation of the two craft. Such formation flying will be maintained for 6 hours, creating ″artificial solar eclipse″ for the satellite below. The spacecraft pair will fly a highly elliptical orbit divided between periods of accurate formation flying around apogee, when payload operations will be possible, and periods of free flight.