Thermally Stable Lightweight Mirrors for Earth Observing Instruments

Lightweight telescopes are a key technology for the remote sensing of earth. Examples of applications for modest size aperture telescopes for earth observation include: GIFTS, GOES, VIIRS for science missions, SBIRS low and SBIRS high for military missions, and Orbview, Ikonos, and Quickbird for commercial remote sensing missions. Earth observation often contains significant transient thermal loads. This load can be sufficient to cause aberrations that exceed limits for diffraction limited optics. Traditional lightweight mirror materials have high stiffness to density ratios. However, hybrid mirrors constructed of glass facesheets and carbon fiber composite support ribs have low thermal expansion and high thermal conductivity making them robust to solar heat loads. We propose to accomplish four goals with the Phase I effort: compare the thermal distortion performance of hybrid mirrors with traditional designs, optimize the design of a hybrid mirror for earth-observing applications, develop a test plan to demonstrate the performance of a hybrid mirror under radiative heat loading conditions, and manufacture a hybrid mirror substrate. The Phase II effort will concentrate on optical polishing of the substrate, testing of the hybrid mirror, and application of the technology to a pending mission.