CHAPS-D: The Compact Hyperspectral Air Pollution Sensor–Demonstrator

Targeted observations of atmospheric trace gases at high spatial resolution are important for characterizing the sources, distribution, and evolution of anthropogenic pollution. The Compact Hyperspectral Air Pollution Sensor (CHAPS) is an imaging spectrometer designed for a 6U CubeSat to fill this need. Miniaturization of this instrument was enabled through the use of freeform optics, additive manufacturing (AM), and topology optimization (TO). We developed the CHAPS–Demonstrator (CHAPS-D) with support from NASA’s Earth Science Technology Office and will demonstrate the feasibility of AM and TO in reducing volume and mass while advancing its technology readiness level (TRL) for future space instrument applications.The CHAPS team selected the requirements for this demonstrator instrument to closely match the requirements for a space-borne mission. A spectral range of 300-500 nm (@ 0.6-nm resolution), a signal to noise ratio (SNR) greater than 500, and a spatial resolution of 1 km x 1 km were selected for science-relevant NO
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measurements from an orbit of 400-600 km. The airborne demonstrator will fly at an altitude of roughly 8 km. We have self-imposed a 6U CubeSat payload total instrument volume constraint. Several AM metal alloys were evaluated through initial material property studies. We chose Scalmalloy as the ideal candidate for this application due to its structural integrity, closely matched CTE with aluminum 6061, and ease of manufacturing with existing processes and equipment. The optical design of the imaging spectrometer employs a number of freeform elements. After establishing the optical design and stability requirements, along with the thermal and structural constraints of a typical CubeSat environment, the structure was algorithmically designed using topology optimization.The CHAPS team environmentally tested a prototype of the initial TO instrument design, and lessons learned were incorporated into the final instrument demonstrator design. CHAPS-D is scheduled for an aircraft flight out of NASA Langley Research Center in summer of 2024. The instrument will be mounted into a NASA King Air B200 and take atmospheric science data over major population centers. The successful demonstration of this instrument concept will enable a future small satellite mission.