Using the CeSiC material for the WSO-UV spectrographs

The World Space Observatory Ultraviolet (WSO-UV) is a multi-national project lead by the Russian Federal Space Agency (Roscosmos) with the objective of high performance observations in the ultraviolet range. The 1.7 m WSO-UV telescope is equipped with UV spectrographs (responsibility of Russia and Germany) and UV imagers (responsibility of Spain). The UV spectroscopic instrumentation comprises two high resolution echelle spectrographs operating in wavelength ranges of 102–176 nm and 174–310 nm respectively, and a Long Slit Spectrograph designed to operate in the range of 102–310 nm. All three spectrographs represent individual instruments. In order to save mass while maintaining high stiffness, the instruments are combined to a monoblock, World Space Observatory Ultraviolet Spectrographs (WUVS). Due to strict technical requirements stated by the customer the material CeSiC (provided by the company ECM) has been selected for the design of the spectrograph structure. In contrast to aluminium, the stable structure of CeSiC is significantly less sensitive to thermal gradients. No further mechanism for focus correction with high functional, technical and operational complexity and corresponding additional System costs are necessary. Using CeSiC also relaxes the thermal control requirements of ±5°C, which represents a considerable cost driver for the S/C design. The phase B2 study of the WUVS instrument finished in December 2010 in collaboration with Russia and with industrial support of the Kayser–Threde company. It included construction of a Structural Thermal Model (STM) for verification of thermal and mechanical loads, stability with respect to thermal distortions and CeSiC manufacturing feasibility.