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Spaceborne optical lens assemblies serve a wide range of applications, including deep-space exploratory missions, earth weather imagery, satellite reconnaissance, and surveillance. These applications demand operation over a wide range of optical performance metrics and environmental conditions. Systems deployed in space cannot afford to use the limited battery or solar power to energize motors required for maintaining focus and diffraction-limited image quality. Therefore, it is vital to develop and characterize passively athermalized solutions for spaceborne optical assemblies that are isolated from direct human contact or have limited access to power. These multi-lens element systems of varying glass materials are susceptible to small optical property changes between glass melt lots and highly dependent on the opto-mechanical assembly method; this creates large sensitivities within the system design that can result in changes in system level performance parameters. Accurate quantification of the optical system performance over the specified operating temperature range prior to flight is critical for mission success. Collins Aerospace, Mission Systems Optronics has developed an environmental test setup and interferometric wavefront measurement approach capable of quantifying the optical performance over temperature of passively athermalized spaceborne optical assemblies. Interferometric wavefront measurements are performed across the operating temperature range; resulting interferograms are analyzed and decomposed in terms of thermal defocus, low-order aberrations, and RMS wavefront error to assess final system compliance. The laboratory prototype system consists of a 633nm common-path interferometer, nitrogen-purged environmental test chamber, and retro-null reflecting pin. We use an f/3 aerospace lens, intended for deep-space application, to demonstrate these measurement techniques.
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