End-to-end numerical simulator of the Shadow Position Sensor (SPS) metrology subsystem of the PROBA-3 ESA mission

Abstract

PROBA-3 - PRoject for OnBoard Autonomy is an ESA mission to be launched in 2022 where a spacecraſt is used as an external occulter (OSC-Occulter Spacecraſt), to create an artificial solar eclipse as observed by a second spacecraſt, the coronagraph (CSC-Coronagraph Spacecraſt). The two spacecraſts (SCs) will orbit around the Earth, with an highly elliptic orbit (HEO), with the perigee at 600 Km, the apogee at about 60530 Km and an eccentricity of 0.81. The orbital period is of 19.7 hours and the precise formation flight (within 1 mm) will be maintainedforabout6hours overthe apogee, in ordertoguarantee the observation ofthe solarcoronawith the required spatial resolution. The relative alignment ofthe two spacecraſts is obtained bycombining information from several subsystems. One ofthe most accurate subsystem (with accuracy >0.5 mm) is the Shadow Position Sensors (SPS), composed by eight photomultipliers installed around the entrance pupil of the CSC. The SPS will monitor the penumbra generated by the occulter spacecraſt, whose intensity will change according to the relative position ofthe two satellites. A dedicated algorithm has been developed to retrieve the displacementof the spacecraſts fromthe measurements ofthe SPS. Several tests are requiredin ordertoevaluate the robustness of the algorithm and its performances/results for different possible configurations. A soſtware simulator has been developed for this purpose. The simulator includes the possibility to generate synthetic 2-D penumbra profile maps or analyze measured profiles and run different versions ofthe retrieving algorithms, including the “on-board” version. In order to import the “as built” algorithms, the soſtware is coded using Matlab.