Abstract: Because of the light weight, the stable dielectric properties and the good electric strength, the ceramic materials are widely used for the padding function in communication products of spacecraft. In this paper, the structure, the morphologies of the fracture surface, and the mechanical and dielectric properties are studied. The influences of the structural anisotropy and the space environment on the mechanical and electrical properties are analyzed. It is shown that the ceramic materials have a low total mass loss (TML), a low collected volatile condensable material (CVCM) content and a high radiation resistance. The strength is found decreasing after the high moisture treatment by the absorption of water, which makes the B₂O₃ react with the water to form boric acids with pretty low strength.