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Proceedings Paper • Open Access

Preliminary error budget analysis of the coronagraphic instrument metis for the solar orbiter ESA mission
Author(s): Vania Da Deppo; Luca Poletto; Giuseppe Crescenzio; Silvano Fineschi; Ester Antonucci; Giampiero Naletto

Paper Abstract

METIS, the Multi Element Telescope for Imaging and Spectroscopy, is the solar coronagraph foreseen for the ESA Solar Orbiter mission. METIS is conceived to image the solar corona from a near-Sun orbit in three different spectral bands: in the HeII EUV narrow band at 30.4 nm, in the HI UV narrow band at 121.6 nm, and in the polarized visible light band (590 – 650 nm). It also incorporates the capability of multi-slit spectroscopy of the corona in the UV/EUV range at different heliocentric heights.

METIS is an externally occulted coronagraph which adopts an “inverted occulted” configuration. The Inverted external occulter (IEO) is a small circular aperture at the METIS entrance; the Sun-disk light is rejected by a spherical mirror M0 through the same aperture, while the coronal light is collected by two annular mirrors M1-M2 realizing a Gregorian telescope. To allocate the spectroscopic part, one portion of the M2 is covered by a grating (i.e. approximately 1/8 of the solar corona will not be imaged).

This paper presents the error budget analysis for this new concept coronagraph configuration, which incorporates 3 different sub-channels: UV and EUV imaging sub-channel, in which the UV and EUV light paths have in common the detector and all of the optical elements but a filter, the polarimetric visible light sub-channel which, after the telescope optics, has a dedicated relay optics and a polarizing unit, and the spectroscopic sub-channel, which shares the filters and the detector with the UV-EUV imaging one, but includes a grating instead of the secondary mirror.

The tolerance analysis of such an instrument is quite complex: in fact not only the optical performance for the 3 sub-channels has to be maintained simultaneously, but also the positions of M0 and of the occulters (IEO, internal occulter and Lyot stop), which guarantee the optimal disk light suppression, have to be taken into account as tolerancing parameters.

In the aim of assuring the scientific requirements are optimally fulfilled for all the sub-channels, the preliminary results of manufacturing, alignment and stability tolerance analysis for the whole instrument will be described and discussed.

Paper Details

Date Published: 20 November 2017
PDF: 6 pages
Proc. SPIE 10564, International Conference on Space Optics — ICSO 2012, 105643B (20 November 2017); doi: 10.1117/12.2309067
Show Author Affiliations
Vania Da Deppo, CNR-Istituto di Fotonica e Nanotecnologie (Italy)
Luca Poletto, CNR-Istituto di Fotonica e Nanotecnologie (Italy)
Giuseppe Crescenzio, INAF - Osservatorio Astronomico di Torino (Italy)
Silvano Fineschi, INAF - Osservatorio Astrofisico di Torino (Italy)
Ester Antonucci, INAF - Osservatorio Astronomico di Torino (Italy)
Giampiero Naletto, Univ. of Padova (Italy)

Published in SPIE Proceedings Vol. 10564:
International Conference on Space Optics — ICSO 2012
Bruno Cugny; Errico Armandillo; Nikos Karafolas, Editor(s)

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