M Cubed has developed and patented technology to make carbon fiber reinforced SiC composites and components. In addition, the feasibility of doubling the toughness of SiC with carbon nanotube (CNT) reinforcement has been proven. In this program, M Cubed will demonstrate further innovative modifications of the above technology to make extremely lightweight, high toughness, low CTE optical components. In particular, 0.25 m and 0.5m lightweighted spherical mirror substrates will be fabricated, coated, finished and delivered to NASA for characterization (including cryogenic testing. A path will be outlined to take the technology to 1-2m class mirror in Phase II.