EnVision, ESA's upcoming Venus orbiter, seeks to comprehensively understand the planet's evolution, building on the success of Venus Express. It will map Venus's interior, surface, and atmosphere with unprecedented detail, enhancing insights into its geological evolution [1]. VenSpec-H – one of the instruments within the VenSpec Suite – is focusing on the atmosphere both below and above the clouds as it will analyze volcanic plumes, as well as complementing surface and subsurface observations [2]. The results are foreseen to support the research teams of BIRA-IASB under Instrument Lead (IL) Dr. Séverine Robert and ETH Zürich under Profs. Paul Tackley and Taras Gerya – Co-ILs of the VenSpec-H Instrument – in understanding commonalities and differences between the planetary evolutions of Venus and Earth [3][4]. VenSpec-H is an optical spectrometer using an echelle grating to diffract uniform light for detailed compositional analysis. A cooled spectrometer section is preceded by a band selection section based on a combination of a filter wheel and a fixed horizontal double stripe filter.
This paper focusses on the development approach of the Filter Wheel Mechanism (FWM) lead by the Swiss Team of VenSpec-H (HSLU, ETH, FHNW, KOEGL Space) and its drive electronics lead by BIRA. It also gives insights in the tests that were performed with a detailed breadboard built within phase B1 of the project.
EnVision is ESA’s upcoming mission to Venus with a launch scheduled in 2031. One of the payloads on board is the VenSpec suite,1 containing three spectrometer channels, one of which is VenSpec-H. VenSpec-H (Venus Spectrometer with High resolution) performs absorption measurements in the atmosphere of Venus in four near-infrared spectral bands. VenSpec-H is developed under Belgian management and builds on heritage from instruments on Venus-Express and TGO. Techniques used in these precursor instruments are improved and complemented with new technologies to comply with the scientific goals of the EnVision mission. The operating wavelength range (1.15 - 2.5 μm) imposes stringent temperature requirements on the instrument to make nightside measurements below the Venus clouds possible. Most importantly, the spectrometer’s optical components are held in a separate cold section inside the instrument, cooled down to −45°C, to remove thermal background from the signal. To avoid heat dissipation close to the spectrometer optics, the electronic boards are kept in a separate box. Besides that, some mechanisms, placed in the warmer part of the instrument at the entrance or exit of the cold section, had to be developed: a turn window unit to protect the interior of the instrument during the aerobraking phase of the mission, a filter wheel mechanism to select the spectral bands of interest, and an integrated detector-cooler-assembly to register the spectra. Some passive optical elements in the spectrometer had low technological readiness at the start of the project. One of them is a freeform corrector plate, used to compensate for aberrations introduced in the system by a parabolic mirror. This device is developed by the Brussels Photonics lab of VUB (Brussels) using a supply chain with shape adaptive corrective polishing and dedicated metrology. Another is the echelle grating, used to disperse the incoming light into its spectral components, which is built by AMOS. Both devices are highlighted in this article.
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