Laboratory testbed for the calibration and the validation of the shadow position sensor subsystem of the PROBA3 ESA mission

The PROBA3 mission of the European Space Agency is the first formation flying (FF) mission that will be flown in high elliptic geocentric orbit aiming at verifying and validating different metrology control systems and algorithms in order to realize and maintain the formation of two independent spacecraft, in total autonomy. The final target accuracy for the relative and absolute alignment of the two satellites is of about 2mm over an inter satellite distance of 144.3m. During the FF, the two spacecraft will realize a giant coronagraph with the external occulter on one payload and the telescope on the other one. The Sun Corona observation will be the scientific tool for the FF validation. Between the different metrology systems that will be tested, the Shadow Position Sensor (SPS) is the most challenging one, aiming at returning the relative and absolute position of the formation with the finest accuracy: 0.5mm out of the guidance and navigation and control loop and 2mm within the loop. The mission program is now in the Phase D with the realization and the testing of the flight model. Due to the high expected performance, a fine calibration of the SPS subsystem is mandatory. In this paper, we discuss the radiometric and spectral calibration plan, the algorithm validation procedure, and the laboratory test-bed realized to reproduce the in-flight observation conditions of the SPS by using a set of calibrated LED and a mechanical set-up equivalent to the SPS system. Preliminary results are also reviewed.