CHIME (Copernicus Hyperspectral Imaging Mission for the Environment) is one of the six Sentinel Expansion missions currently developed by EU and ESA, to be launched by the end of the decade. It will provide hyperspectral imagery of the Earth's surface. The mission is expected to have a major impact on our understanding of the Earth's land surface and its processes and will help us to address some of the most pressing challenges facing our planet today by supporting a variety of applications including sustainable agriculture, water management, environmental monitoring, or disaster management. A pair of satellites will each carry a high-performance push broom hyperspectral imager able to measure the reflected light from the Earth's surface in 250 spectral bands over a swath of 130 km, at 30m x 30m ground sampling. The spectrometer system (SPS) consists of three identical spectrometer units (SU). The spectrometers are in a unique staggered and offset arrangement, offering a full swath of about 4500 pixels (including overlaps). The main technological challenges of the spectrometer unit, i.e. the broadband grating and the ultra-accurate long slit have been raised up to TRL6 during the Phase B2 and the final design is now frozen. The main optical and thermo-mechanical analyses are completed as well as the test approach. The manufacturing of the first fully functional Engineering Model is on-going.
Copernicus, the European Union’s programme for observing and monitoring the Earth, represents one of the most successful space programmes coordinated and managed by the European Commission in partnership with ESA, the Member States and Agencies. 2020 marked a major step of the Copernicus expansion programme with the selection of six missions to enter into B2CD implementation, namely CHIME, LSTM, CO2M, CRISTAL, ROSE-L, and CIMR. The CHIME mission (Copernicus Hyperspectral Imaging Mission for the Environment) space segment was awarded to an industrial consortium led by Thales Alenia Space (FR), as Mission Prime, and OHB (DE), as Instrument Prime. Within the instrument team, the responsibility of the design and development of the spectrometer system (SPS) have been assigned to AMOS (BE). The SPS is the centrepiece of the CHIME instrument, ensuring the accurate spectral dispersion of the imaged ground swath over wide focal planes. The SPS consists of three identical spectrometer units drawn from the compact de-magnifying freeform Offner optical solution developed at AMOS. Its throughput is guaranteed by a broadband convex diffraction grating, while the image quality and distortion control are enabled using freeform mirrors. This paper describes the mathematical modelling and prototyping activities, including manufacturing and testing of grating samples, carried by AMOS raising the maturity of the CHIME diffraction grating achieving Technology Readiness Level 6 (TRL6).
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