The large scale light-weight silicon carbide(SiC) mirror blanks at 620 mm and 700 mm×300 mm were prepared with gel-casting method. After drying

burning out the organic elements

infiltrating carbon and reaction-sintering

the reaction-bonded SiC (RB-SiC) mirrors were fabricated. The results of ground mirrors show that the structure of RB-SiC is full solid

and the mechanical and thermal properties of RB-SiC are excellent in bending strength of 350 MPa

fracture toughness of 4.1 MPa·m

1/2

and coefficient of thermal expansion (CET) of 2.67×10

－6

/K. The surface roughness (RMS) of the polished mirror is better than 3 nm

it is a fine material for the space-borne large scale light-weight mirror.