Sentinel 5 instrument and UV1 spectrometer subsystem optical design and development

Sentinel-5 is an Earth atmospheric monitoring mission developed within the European Union’s Copernicus program. The mission objective is to monitor the composition of the Earth’s atmosphere on a daily basis. Airbus DS GmbH acts as the prime contractor under a European Space Agency contract. The instrument design, development, and the instrument verification was and is in many aspects a fruitful co-operation between Airbus and TNO. The first part of this paper illustrates the optical design of the five optical channels of the Sentinel 5 instrument. The innovative compact optical design sets the basis for the acquisition of the variety of trace gas spectra. The design includes a two free-form mirror wide field telescope, a pointing insensitive Dual Babinet Pseudo Depolariser type polarisation scrambler, three one-dimensional waveguide type homogenizers, five reflective and refractive anamorphotic spectrometers including different disperser types as an a-spherical reflective diffraction grating for the ultra-violet, a grism for mainly the visible, a transmissive grating for the near-infrared, and immersed reflective gratings for the short wave infrared spectral ranges. The second part of this paper focusses on the design, qualification and verification of the UV1 spectrometer subsystem. Its optical design is based on an Offner-type spectrometer which has been adapted to employ freeform optics and an aspheric off-axis grating. A monolithic housing structure has been developed for optimum stability, accessibility and easy integration of the optical components. The qualification and performance verification of the first Proto Flight Model of the UV1 spectrometer was successfully completed in July 2020.