Metis coronagraph - A system engineering approach

METIS is one of the remote sensing instruments of the Solar Orbiter mission of the European Space Agency (ESA), currently undergoing Critical Design Review under ASI contract awarded to the Italian industries, CGS/TAS- I. The objective of Solar Orbiter is the exploration of the Sun hcliosphere by means of remote sensing and in-situ instruments from a minimum distance of 0.28 AU and from solar latitudes up to 34°. METIS is an inverted-occultation coronagraph specifically designed to acquire simultaneous images of the solar corona in two different wavelengths (visible light between 580 nm and 640 nm, and the Lyman-a line of Hydrogen at 121.6 nm). The visible channel also includes a polarimeter to observe the linearly polarized component of the K corona. METIS is designed with sophisticated technological solutions and innovative materials in order to meet, from one side, the very stringent scientific requirements and, on the other side, the challenging technical and programmatic interfaces with the Solar Orbiter spacecraft. To this end, the Italian Space Agency (ASI), the leading funding agency of the project under the Pl-ship of Prof. E. Antonucci of INAF, Turin, awarded the phase C/D industrial contract to the Compagnia Generale per lo Spazio (CGS) and Thales Alenia Space Italia (TAS-I) for the design, realization and qualification of the instrument. A strong scientific and technical collaboration is in place with the Max Planck Institute for Solar System Research (Goettingen, Germany) and Astronomical Institute of the Academy of Sciences of the Czech Republic, for the provision respectively of the visible and ultraviolet light detector assemblies and the mirrors of the telescope. Finally, in order to be compliant with the very stringent and challenging contamination requirements, ESA has awarded an ad-hoc contract to the Company SENER for the design and realization of a sealing protection cap to be placed on top of the aperture of the telescope and ejected on orbit.