Abstract

The need for increasingly large, precision optical instruments presents severe impediments for space-based systems. These difficulties arise due to the limited payload size and weight than can be lofted into earth orbit by available launch vehicles. Size limitations can be overcome, at the expense of increased complexity, by dividing the aperture into multiple segments, which may be unfolded or otherwise reassembled after achieving orbit. Other problems exist in regard to weight, however. In the absence of gravity, structures may be lightweighted to an extreme degree with limits only imposed by factors such as vibration, thermal, and inertial loads. Optical surfaces, on the other hand, must be manufactured and tested to precise, absolute shapes in a one-g environment. The problem to be solved then becomes one of a trade between stiffness and weight versus deployment and manufacture. Ultimately, launch weight reduces to optimization of specific stiffness, which considers not only materials' properties but fabricability as well. Because of the favorable mechanical and thermal properties of silicon carbide, special manufacturing methods have been developed to produce mirror substrates with areal densities of 15 kg/m² or less. This paper will discuss application of this material and precision forming process, to large lightweight optical systems, and will compare mechanical and thermal figures of merit to other material candidates. Some examples of this process as applied to prototype mirrors will also be shown.

© 1990 Optical Society of America