Full-SiC EUCLID's very large telescope

Euclid is a part of the European Space Agency Cosmic Vision Medium Class program. This mission's goal is to investigate the nature of dark energy, dark matter and gravity by observing the geometry of the Universe and the formation of structures over cosmological timescales. Euclid Payload Module (PLM) includes a large three mirrors anastigmatic Korsch telescope feeding a visible imager (VIS) and a near-infrared spectrometer and photometer (NISP). The hardware of all of them will be mainly made of Boostec (R) SiC material. The SiC telescope has been designed by Airbus Defence and Space team in Toulouse (France). The PLM is divided in two cavities which are separated and hold by a very large SiC baseplate; the front one includes the primary and secondary mirrors and the associated support structure while the back one consists of the telescope folding mirrors, the tertiary mirror, the two instruments (VIS and NISP) and other optical devices. The focal length is 24.5 m and the useful pupil diameter is 1.2 m. A passive thermal concept has been developed, thus requiring minimum heating power and providing best thermal stability. The telescope will operate at approximate to 130 K. In addition to its high thermal conductivity, the Boostec (R) SiC has been chosen for its mechanical properties and its ability to greatly reduce mass. The full SiC telescope architecture gives high optical stability. The present paper describes the very large full-SiC telescope and the manufacturing process of its SiC parts, in particular the mirrors, the lightweight baseplate and the spider.