Adverse air quality impacts human health and climate and has implications for environmental equity. The Compact Hyperspectral Air Pollution Sensor (CHAPS) is a newly designed small imaging spectrometer for remote sensing of nitrogen dioxide (NO2) and other air pollutants from space. It incorporates two emerging technologies, to achieve the miniaturization necessary to fit within a 6U CubeSat. The first is freeform optics, which can be used to reduce the size of an imaging spectrometer without compromising optical performance. We report the science requirements; preliminary, fully freeform and fully reflective optical design of the CHAPS demonstrator, CHAPS-D; and model its performance. The second technology is additive manufacturing, coupled with topology optimization, which has a number of potential advantages over traditional subtractive manufacturing. The instrument mechanical structure, including optical mounts and integral light baffles, and two of the optical elements will be additively manufactured using a high-strength nextgeneration aluminum alloy. We show preliminary results of additive manufacturing tests. CHAPS-D is currently being developed for ground-based and airborne testing.
Within the Copernicus program, the Sentinel-5/UVNS instrument is dedicated to the monitoring of air quality, trace gases and aerosols. The instrument consists of two co-aligned telescopes and five spectrometers in the spectral channels named UV1, UV2VIS, NIR, SWIR1, and SWIR3. The spectral band of UV1 spectrometer is defined from 270 nm to 310 nm. To distribute incoming light and eliminate false light into the channels and within the UV1 channel dedicated coatings for UV spectral range are needed. OBJ was selected for development and application of these coatings.
Jess Köhler, Rik Jansen, Juan Irizar, Alexander Sohmer, Markus Melf, Robert Greinacher, Matthias Erdmann, Volker Kirschner, Abelardo Pérez Albiñana, Didier Martin, Bryan de Goeij, Rob Vink, James Day, Daniël Ten Bloemendal, Wim Gielesen, Jan de Vreugd, Ludger van der Laan, Adriaan van’t Hof
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.
Sentinel-5 is an Earth atmospheric monitoring mission developed within the Copernicus program. The mission objective is to monitor the composition of the Earth’s atmosphere on a daily basis. TNO is developing the UV1 spectrometer subsystem as well as the two telescope subsystems. In this paper, the design of the UV1 spectrometer is described and its major design and verification challenges are discussed.
The UV1 optical design is based on a classical Offner-type spectrometer which has been adapted to employ freeform optics and an aspheric off-axis grating. It generates a magnification of 0.4. A structural, monolithic housing has been designed that is optimized for stability, accessibility and integration of optical components. To realize a thermo-mechanically stable construction, both housing and mirror bodies are built from aluminum. Four out of five mirrors have a dedicated black coating for absorbing out-of-band light. For further stray light suppression, a graded short-pass filter is employed on the last optical element just in front of the detector.
Performance verification of a standalone spectrometer without telescope, entrance slit, limiting aperture stop and flight detector is a major challenge. For this verification TNO developed dedicated ground support equipment that will be used under both ambient and vacuum conditions; a dedicated optical stimulus that mimics the illumination from the telescope in terms of pointing and NA, a Slit Assembly that mimics the homogenizer entrance slit and a Test Detector to determine the image plane and to measure the optical performance with high accuracy.
At the time of writing this article, the first (proto-flight) model has been aligned and performance verification is about to start.
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