Since years Alcatel Space is interested in the development of a new material to produce lightweight, stable and cost effective structures and mirrors for space instrument. CeSiC from ECM has been selected for its intrinsic properties (high specific modulus, high conductivity, low thermal expansion coefficient and high fracture toughness), added to ample manufacturing capabilities. Based on first results on a full scale demonstration model made under own R&D project funding, Alcatel Space is now in position to propose for space project this technology mastered in common with ECM. In the frame of NIRSPEC project, instrument of JWST, an optical bench breadboard made of CeSiC has been designed, manufactured and tested under ESA contract. The aim of this breadboard was to confirm the high lightweight capabilities of CeSiC technology on such large and complex structure, its strength and stability under vibration and cryogenic environment, and therefore its capability to be used for the NIRSPEC optical bench. In addition, a database of this material has been built, thanks tests performed by Alcatel Space and by ECM, with the support of an additional specific ESA contract. Other immediate application is the use of CeSiC for large and lightweight space telescopes mirrors which shall be cladded for polishing and reach roughness up to visible range applications needs. CeSiC is also foreseen for the future generation of focal plane offering a very stable structure holding all the detectors thanks to CeSiC rigidity and stability performances, and its high thermal conductivity.