Formation flying is one of the most promising techniques for the future of astronomy and astrophysics from the space.
The capabilities of the rockets strongly affect the dimensions and the weights of telescopes and instrumentation to be
launched. Telescopes composed by several smallest satellites in formation flying, could be the key for build big space
telescopes. With this aim, the ESA PROBA-3 mission will demonstrate the capabilities of this technology, maintaining
two satellites aligned within 1 mm (longitudinal) when the nominal distance between the two is of around 144m.
The scientific objective of the mission is the observation of the solar corona down to 1.08 solar radii. The Coronagraph
Spacecraft (CSC) will observe the Sun, when the second spacecraft, the Occulter Spacecraft (OSC) will work as an
external occulter, eclipsing to the CSC the sun disk. The finest metrology sub-systems, the Shadow Position Sensors
(SPS) and the Occulter Position Sensor Emitters (OPSE) identifying respectively the CSC-Sun axis and the formation
flying (i.e., CSC-OSC) axis will be considered here. In particular, this paper is dedicated to the test-bed for the
characterization, the performance analysis and the algorithms capabilities analysis of the both the metrology subsystems.
The test-bed is able to simulate the different flight conditions of the two spacecraft and will give the opportunity to check
the response of the subsystems in the conditions as close as possible to the flight ones.