Herschel main mirror made from SiC petals

The 'blank' for Herschel's main mirror wss 3.5 metres in diameter and was fabricated by brazing together 12 segments. The segments were formed by isostatic pressing and sintering of silicon carbide. The mirror blank became the biggest silicon carbide structure in the world and the completed mirror became the largest single-component telescope reflector ever made for use in space.