The EnVisS (Entire Visible Sky) instrument is one of the payloads of the European Space Agency Comet Interceptor mission. The aim of the mission is the study of a dynamically new comet, i.e. a comet that never travelled through the solar system, or an interstellar object, entering the inner solar system. As the mission three-spacecraft system passes through the comet coma, the EnVisS instrument maps the sky, as viewed from the interior of the comet tail, providing information on the dust properties and distribution. EnVisS is mounted on a spinning spacecraft and the full sky (i.e. 360°x180°) is entirely mapped thanks to a very wide field of view (180°x45°) optical design selected for the EnVisS camera. The paper presents the design of the EnVisS optical head. A fisheye optical layout has been selected because of the required wide field of view (180°x45°). This kind of layout has recently found several applications in Earth remote sensing (3MI instrument on MetOp SG) and in space exploration (SMEI instrument on Coriolis, MARCI on Mars reconnaissance orbiter). The EnVisS optical head provides a high resolved image to be coupled with a COTS detector featuring 2kx2k pixels with pitch 5.5µm. Chromatic aberration is corrected in the waveband 550-800nm, while the distortion has been controlled over the whole field of view to remain below 8% with respect to an Fθ mapping law. Since the camera will be switched on 24 hours before the comet closest encounter, the operative temperature will change during the approaching phase and crossing of the comet’s coma. In the paper, we discuss the solution adopted for reaching these challenging performances for a space-grade design, while at the same time respecting the demanding small allocated volume and mass for the optical and mechanical design. The view expressed herein can in no way be taken to reflect the official opinion of the European Space Agency.
In the frame of the ESA Sentinel-5 mission, as part of the Copernicus program, Airbus is the prime contractor for the S5 Instrument. As part of the S5 instrument, which is using the METOP SG satellite as a platform, Leonardo is developing the Short-Wave Infrared Spectrometer (SWIR-SS), comprising two parallel channels covering the wavelength ranges of 1589÷1676 nm (SWIR 1) and 2304÷2386 nm (SWIR 3). Major objective of the S5 is the monitoring of the Earth atmosphere by taking measurements of trace gases and aerosols impacting air quality and climate, with a swath width of ca. 2670 Km providing daily coverage of Earth atmosphere at an unprecedented resolution of 7x7 Km2 at nadir. Main characteristic of the SWIR-SS compared to other spectrometers is the high spectral position one orbit stability less than 1um and high spectral pixel resolution of 0.1nm. High stability and optical quality requires accurate optical elements mounting design and high resolution is reached by using new developments regarding Immersed Grating (grating immersed on a prism) and the implementation of a cutting edge 3D Slit Homogenizer system, positioned on the object plane of the spectrometer, to mitigate radiometric errors arising from scene heterogeneity. In order to demonstrate the system performance the optical design has been validated by means of flight representative optical assemblies. These breadboards are representing all relevant optical elements of the system. This paper presents the tests, which have been performed on the flight representative optical elements and the test results. As the Optical Element Mounting, the Slit Homogenizer and the Immersed Grating are major elements to fulfil mission requirements the development approach is described. Special emphasis for Lens mounting is put on the stability and WFE, for the Slit Homogenizer is put on the requirements regarding the slit width variation and the quality of the entrance edge while the major design driver for the Immersed grating is the optical quality. This paper presents the development approach of these two major optical elements and the validation test results.
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