Earth observation and greenhouse gas sensing from space provides vital information for climate and climate change monitoring, indicating the importance of novel spaceborne telescopes and spectrometers. We present a novel freeform pushbroom imaging spectrometer enabling the sensing of water vapor, carbon dioxide and methane in the atmosphere, while fitting within 2 CubeSats Units. The design comprises a 2-mirror freeform telescope, combined with a near-infrared (1100 – 1700 nm) spectrometer featuring 3 freeform mirrors and a reflective grating, providing both spatial and spectral information using a 2D detector. All mirrors are described and optimized using XY polynomials, enabling a nearly diffraction-limited performance. The novel design is exceeding the state-of-the-art, by showing a full FOV of 120°, a spatial resolution of 2.6 km, and a spectral resolution of 13 nm. According to our knowledge, our novel design shows the widest field-of-view that has ever been realized for space-based telescopes, nearly reaching Earth observation from limb to limb from an altitude of about 700 km. The freeform telescope mirrors were manufactured in-house using high-precision 5-axis milling and 5-axis ultraprecision diamond tooling. Finally, a laboratory proof-of-concept demonstrator was realized validating the field-of-view and focusing spot sizes, paving the way for future space missions that target wide field-ofview imaging and/or an enhanced climate monitoring.
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