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Proceedings Paper • Open Access

PROBA-3 formation-flying metrology: algorithms for the shadow position sensor system
Author(s): M. Casti; A. Bemporad; S. Fineschi; G. Capobianco; D. Loreggia; V. Noce; F. Landini; C. Thizy; D. Galano; R. Rougeot

Paper Abstract

PROBA-3 ESA’s mission aims at demonstrating the possibility and the capacity to carry out a space mission in which two spacecrafts fly in formation and maintain a fixed configuration. In particular, these two satellites - the Coronagraph Spacecraft (CSC) and the Occulter Spacecraft (OSC) – will form a 150-meters externally occulted coronagraph for the purpose of observing the faint solar corona, close to the solar limb – i.e. 1.05 solar radii from the Sun’s center (RΘ). The first satellite will host the ASPIICS (Association de Satellites Pour l'Imagerie et l'Interférométrie de la Couronne Solaire) coronagraph as primary payload. These features give to the PROBA-3 mission the characteristics of both, a technological and a scientific mission.

Several metrology systems have been implemented in order to keep the formation-flying configuration. Among them, the Shadow Position Sensors (SPSs) assembly. The SPSs are designed to verify the sun-pointing alignment between the Coronagraph pupil entrance centre and the umbra cone generated by the Occulter Disk. The accurate alignment between the spacecrafts is required for observations of the solar corona as much close to the limb as 1.05 RΘ.The metrological system based on the SPSs is composed of two sets of four micro arrays of Silicon Photomultipliers (SiPMs) located on the coronagraph pupil plane and acquiring data related to the intensity of the penumbra illumination level to retrieve the spacecrafts relative position. We developed and tested a dedicated algorithm for retrieving the satellites position with respect to the Sun. Starting from the measurements of the penumbra profile in four different spots and applying a suitable logic, the algorithm evaluates the spacecraft tri-dimensional relative position. In particular, during the observational phase, when the two satellites will be at 150 meters of distance, the algorithm will compute the relative position around the ideal aligned position with an accuracy of 500μm within the lateral plane and 500 mm for the longitudinal measurement. This work describes the formation flying algorithm based on the SPS measurements. In particular, the implementation logic and the formulae are described together with the results of the algorithm testing.

Paper Details

Date Published: 12 July 2019
PDF: 10 pages
Proc. SPIE 11180, International Conference on Space Optics — ICSO 2018, 1118082 (12 July 2019); doi: 10.1117/12.2536209
Show Author Affiliations
M. Casti, INAF – Osservatorio Astrofisico di Torino (Italy)
A. Bemporad, INAF – Osservatorio Astrofisico di Torino (Italy)
S. Fineschi, INAF – Osservatorio Astrofisico di Torino (Italy)
G. Capobianco, INAF – Osservatorio Astrofisico di Torino (Italy)
D. Loreggia, INAF – Osservatorio Astrofisico di Torino (Italy)
V. Noce, INAF – Osservatorio Astrofisico di Torino (Italy)
F. Landini, INAF – Astrophysical Observatory of Arcetri (Italy)
C. Thizy, Ctr. Spatial de Liège (Belgium)
D. Galano, European Space Research and Technology Ctr. (Netherlands)
R. Rougeot, European Space Agency (Netherlands)

Published in SPIE Proceedings Vol. 11180:
International Conference on Space Optics — ICSO 2018
Zoran Sodnik; Nikos Karafolas; Bruno Cugny, Editor(s)

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