Cubesat multispectral space-based imaging spectrometer enhancing climate change monitoring

Space-based spectrometers are of high importance for Earth observation and greenhouse gas sensing. We present a novel freeform pushbroom imaging spectrometer, covering the visible (400 - 1100 nm), near-infrared (1100 - 1700 nm) and thermal (8 - 14 mu m) wavelength range, showing a full field-of-view of 120 degrees, while fitting within a single CubeSat Unit. The design is composed of a freeform 2-mirror telescope, followed by a freeform spectrometer unit. The freeform telescope guides the light to the spectrometer entrance slit, after which a collimating mirror is present, and the light is split to the 3 spectrometer channels. Each spectrometer channel focuses the light onto a 2D detector providing both spatial and spectral information. The visible spectrometer channel comprises a transmission diffraction grating followed by 2 freeform mirrors, enabling a nadir spatial resolution of 9.87 km and a spectral resolution of 5.18 nm. The near-infrared and thermal spectrometer each comprise a reflective diffraction grating and 2 freeform mirrors, featuring a nadir spatial resolution of 4.13 km and 9.31 km, and a spectral resolution of 2.74 nm and 48.27 nm, respectively. All mirrors are described using XY polynomials, up to the 4th order, enabling a close to diffraction-limited performance. Consequently, this design might benefit future space missions enabling an improved Earth observation and climate monitoring.