Down along the main corridor of a European Space Agency facility in the Netherlands, researchers tested a novel targeting system that is designed to allow two spacecraft to fly in a precise formation.
Slated to be launched in 2023, ESA’s twin Proba-3 spacecraft are designed to enable researchers to observe the inner layers of the sun’s faint atmosphere, or corona, which are normally obscured in intense sunlight.
In order to observe the sun’s corona, one of the two spacecraft, the Occulter, will block the blinding solar disk for the other, the Coronagraph. To do this, the two spacecraft will utilize a “vision-based sensor system” to fly in a precise formation enabling the Occulter to cast a shadow on the Coronagraph at distances of between 20 and 250 meters.
The vision-based sensor system is made up of two cameras fitted to the Occulter that will look for and lock onto a pattern of pulsing LEDs on Coronagraph. This method is designed to enable the system to estimate the relative position of the two spacecraft down to a few millimetres.
As development of the targeting system progressed, researchers required a long indoor space that could be used to simulate the operational distances. ESA’s ESTEC technical centre in the Netherlands was selected thanks to its 230-meter main corridor.
A square-metre LED target similar to the one that will be installed on the Occulter was placed at 30-meter intervals down the length of the corridor. A specially calibrated lamp was then placed behind the targeting system to simulate stray solar light. The system’s accuracy was then tested at each of the 30-meter intervals.
In addition to distance testing, ESTEC’s Guidance Navigation and Control Rendezvous, Approach and Landing Simulator (GRAILs) was utilized to test if the system’s software could continuously calculate its relative dynamic trajectory. This was achieved by placing a small target on a robotic arm that moved along a pre-programmed path as the system’s cameras observed it.
According to ESA, testing of the Proba-3 mission’s vision-based sensor system yielded “promising results.”
Work on Proba-3 began in October 2006 with a preliminary design review conducted in the fall of 2012. In 2014, Spanish engineering company SENER was selected as the prime contractors for the mission. Additional contracts were also awarded to companies from more than 10 European nations.
The two Proba-3 spacecraft had initially been slated to be launched aboard an Arianespace Vega rocket in 2020. However, the launch has since slipped with it now scheduled for 2023.