Glyndwr Innovations Limited (GIL) has a requirement to use a Ritchey-Common optical test during the processing and final verification of a large elliptical flat mirror. The geometry of the test requires a reference sphere that is larger in diameter than the minor axis of the optical flat under test. In this implementation, the reference sphere measures approximately 60 inches in diameter, has an aspect ratio of 9:1, is a meniscus shape and has a mass of 430kg. The reference sphere support uses a tunable Schwesinger design, supporting the mirror radially, in a horizontal line of sight. FEA predicts the full aperture optical surface deformation resulting from the effects of gravity and the support of the mirror to be 95.9nm RMS, once optimized. Once integrated and tuned the interferometric testing delivers an actual optical surface deformation of 134mn RMS, with the key Zernike terms being spherical and trefoil aberrations. The final optical form of the reference sphere, measured over its illuminated diameter within the optical test, meets our test wavefront requirements.
We describe the development of a lightweight, high-resolution surveillance camera for deployment on high altitude platform systems. The instrument is designed to operate at an altitude of ∼20 km and has an expected ground resolution of better than 120 mm with an appropriate sensor. While designed specifically for imaging at visible wavelengths, it is shown that the design is capable of diffraction-limited imaging at NIR and SWIR wavelengths up to 2.5 μm. We have combined a range of materials from aluminum and titanium alloys through to carbon fiber-reinforced plastic to produce an instrument with structural components that match the thermal expansion of the optical glasses used. The use of these materials has resulted in an instrument that weighs <2 kg, including a sensor package, and is designed to weigh <3 kg once integrated with an enclosure and actuated gimbal. The successful testing of two prototype systems is described, including several design outcomes from the program intended for implementation in advance of flight trials.
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