Aluminum mirrors offer the advantages of lower cost, shorter fabrication time, more rugged mounting, and same
material athermalization when compared to classical glass mirrors. In the past these advantages were offset by
controversial dimensional stability and high surface scatter, limiting applications to IR systems. Raytheon developed
processes to improve long term stability, and reduce surface scatter. Six 380 mm aperture aluminum mirrors made using
these processes showed excellent stability, with figure changes of less than 0.01 wave RMS(1 wave = 633 nm) when
cycled 10 times between -51 and +71 deg. C. The VQ process developed at ELCAN reduces surface scatter in bare
aluminum mirrors to below 20 angstroms RMS, and has been used in thousands of production mirrors up to 300 mm
aperture. These processes were employed in the fabrication of two lightweight single arch 600 mm aluminum mirrors.
The two mirrors were produced in four months, with a mounted surface figure of 0.22 waves RMS and surface
roughness of 20 angstroms. Mounted fundamental frequency was 218 Hz, and no figure distortion was observed at
preload levels four times higher than design. Subsequently the mirrors performed well when subjected to severe
environmental loadings in a Raytheon test system. This technology is being extended to ultra-lightweight sandwich
mirrors, which are competitive with other material technologies used in advanced aerospace applications such as high-altitude
UAV surveillance systems and satellite optics.