The analysis for solid mirrors sets the stage for the analysis of lightweight optics. Weight is extremely critical for airborne and space optical systems to meet the limitations of fuel consumption, load capacity, and cost. Groundbased systems also have weight limits due to transport, lift, assembly, and other requirements, particularly for large-aperture assemblies. The 200-in. (5-m) Hale Telescope, for example, operating at Mount Palomar, was made using one of the early lightweight mirror approaches. The cast borosilicate optic was about 35% lightweighted compared to a solid of equal depth. This is a far cry from today’s lightweighting capabilities, which can exceed 90% weight reduction from the parent solid. By comparison, the 5-m Hale Telescope has a mass density of 900 kg/m2, while the 6-m JamesWebb Space Telescope primary optic has a mass density of less than 20 kg/m2.
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