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.
For ESA’s EnVision Mission to Venus, a consortium of three spectrometers from across Europe has been formed to collaborate not only on the management and science aspects, but also on the technical implementation. One important technical goal of the VenSpec suite is to implement a clean, simple and robust interface to the spacecraft and to provide an abstraction layer between the channels and the spacecraft. This is achieved by implementing the Central Control Unit (CCU), which provides a harmonized power and data interface to the spacecraft and allows the channels to design for a simple tailored internal interface to the CCU. The CCU consists of two electrical subsystems, the Data Handling Unit (CCU DHU), developed by the Max Planck Institute for Solar System Research (MPS) in Göttingen and the Institute of Computer and Network Engineering (IDA) in Braunschweig and the Power Supply Unit (CCU PSU), developed by the Instituto de Astrofísica de Andalucía (IAA-CSIC) in Granada, the system responsibility being at the DLR Institute of Planetary Research (DLR-PF) in Berlin. Within this framework, an extended electrical architecture trade-off was performed in 2023 to optimize the system, guaranteeing the requested functionality and complying to requirements from all sides. As a result of the trade-off. a single power and data interface were found to be the most suitable and robust solution considering performance, reliability, Fault Detection Isolation and Recovery (FDIR) and Electromagnetic Compatibility (EMC) considerations as well as the complexity of the associated verification campaign. This paper demonstrates the options that were suggested by the different parties and justifies the final architecture, which has been chosen to achieve the best solution for the VenSpec suite.
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