Design and integration of a SWIR objective lens for the space-borne DRAGO-2 optical system

Matia-Hernando, Paloma; Berdiñas, Zaira M.; Ynigo, Alfonso; González de Chaves, Pablo; Sánchez, Carlos; Vizuete, Adrián.; Oriol, Jorge; Siegel, Thomas; de la Fuente, Marta
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Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series

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We present the design of the objective lens for the DRAGO-2 optical system, a compact SWIR camera designed for the space environment. DRAGO-2 is the long-focal variant of the DRAGO (Demonstrator of Remote Analysis of Ground Observations) series, developed for the ALISIO-1 mission of the IACTEC-Space team at the Instituto de Astrofísica de Canarias (IAC). The objective lens has a refractive design covering the two bands in the SWIR range (1.1 and 1.6 μm) which is passively athermalized for operation between -20 °C and 40 °C, with a focal length of 150 mm and a focal length variation over the whole temperature range of under 0.2%. The system has an f/# of 4.5, both transmission and relative illumination above 90%, and low distortion under 0.05%. The optical quality is excellent, with an as-built modulation transfer function (MTF) value at 30 cy/mm over 55% on axis and over 40% at the edge of the 6.2 mm diagonal image field to ensure pixel-limited performance. Straylight and finite-element analysis ensure optimal optical performance as well as survival to the environment. Several units of the objective lens have been manufactured with special attention to environmental requirements in terms of both assembly processes and material selection, and their optical performance has been found to be in excellent compliance with the projected as-built optical quality.