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Proceedings Paper

Improved stray light suppression performance for the solar orbiter/METIS inverted external occulter
Author(s): Federico Landini; Marco Romoli; Gerardo Capobianco; Sebastien Vives; Silvano Fineschi; Giuseppe Massone; Davide Loreggia; Enzo Turchi; Christophe Guillon; Clement Escolle; Maurizio Pancrazzi; Mauro Focardi
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Paper Abstract

The Solar Orbiter/METIS visible and UV coronagraph introduces the concept of occulter inversion in solar coronagraphy. Classical externally occulted coronagraphs usually have a disk in front of the telescope entrance pupil. According to the mission requirements, in order to reduce the amount of power entering the instrument and to limit the instrument dimensions, METIS is equipped with an inverted external occulter (IEO). The IEO consists of a circular aperture on the Solar Orbiter thermal shield that acts as coronagraph entrance pupil. A spherical mirror (M0), located ~800 mm behind the IEO, rejects back the disk-light through the IEO itself. A light-tight boom connects the IEO to the M0 through the thermal shield. In order to achieve high performance in stray light suppression, the IEO design needs optimization. Due to the novelty of the concept we can only use the heritage of past space-borne coronagraph occulters as a starting point to design a dedicated occulter optimization shape. A 1.5 years long, accurate test campaign has been carried out to evaluate the best optimization configuration for the IEO. Two prototypes were manufactured to take into account the impact of the boom geometry on the stray light suppression performance. Two optimization concepts were compared: the inverted cone (that derives from the conic optimization of classical occulting disks) and the serrated edge, of which several samples were manufactured, with different geometrical parameters, surface roughnesses and coatings. This work summarizes the activity we have been carrying on to define the flight specifications for the METIS occulter.

Paper Details

Date Published: 26 September 2013
PDF: 19 pages
Proc. SPIE 8862, Solar Physics and Space Weather Instrumentation V, 886204 (26 September 2013); doi: 10.1117/12.2024209
Show Author Affiliations
Federico Landini, INAF - Osservatorio Astrofisico di Arcetri (Italy)
Marco Romoli, Univ. degli Studi di Firenze (Italy)
Gerardo Capobianco, INAF - Osservatorio Astrofisico di Torino (Italy)
Sebastien Vives, Lab. d'Astrophysique de Marseille, CNRS, Aix Marseille Univ. (France)
Silvano Fineschi, INAF - Osservatorio Astrofisico di Torino (Italy)
Giuseppe Massone, INAF - Osservatorio Astrofisico di Torino (Italy)
Davide Loreggia, INAF - Osservatorio Astrofisico di Torino (Italy)
Enzo Turchi, Lab. Meccanico Enzo Turchi, Univ. degli di Firene (Italy)
Christophe Guillon, Lab. d'Astrophysique de Marseille, CNRS, Aix Marseille Univ. (France)
Clement Escolle, Lab. d'Astrophysique de Marseille, CNRS, Aix Marseille Univ. (France)
Maurizio Pancrazzi, INAF - Osservatorio Astrofisico di Arcetri (Italy)
Mauro Focardi, INAF - Osservatorio Astrofisico di Arcetri (Italy)


Published in SPIE Proceedings Vol. 8862:
Solar Physics and Space Weather Instrumentation V
Silvano Fineschi; Judy Fennelly, Editor(s)

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