Discontinuous silicon carbide reinforced aluminum metal matrix composites (MMC) are a unique class of advanced engineered materials which have been developed and recently qualified for use in aerospace structures, inertial guidance systems, and lightweight optical assemblies. Such materials are as light as aluminum but exhibit significantly greater strengths and specific stiffness. Certain grades of these MMC's are isotropic and are more resistant to compressive microcreep than beryllium; and they can be tailored to match the coefficients of thermal expansion (CTE) of other materials, including beryllium, stainless steel, and electroless nickel. Since these composites can be easily forged, superplastically formed, and precision machined into complex shapes, they are ideal for use in the economical production of stable optical systems. This paper describes some of the enhanced properties of engineered MMC's, discusses some of the design considerations that have led to the specification of these materials for building an ultra-lightweight telescope, and presents some interesting results obtained from prototype testing.