In June 2020 NASA has selected the VERTIAS Discovery mission to Venus for flight. The Venus Emissivity Mapper (VEM) provided by DLR together with the VISAR radar system provided by JPL are the core payload of the mission. VEM is the first flight instrument designed with a focus on mapping the surface of Venus using atmospheric windows around 1 μm wavelength. It will provide a global map of surface composition by observing with six narrow band filters from 0.86 to 1.18 μm. Continuous observation of Venus’ thermal emission will place tight constraints on current day volcanic activity. Eight additional channels provide measurements of atmospheric water vapor abundance as well as cloud microphysics and dynamics and permit accurate correction of atmospheric interference on the surface data. Combining VEM with a high-resolution radar mapper on the NASA VERITAS and ESA EnVision missions will provide key insights in the divergent evolution of Venus. After several years of pre-development including the setup of a laboratory prototype the implementation for flight has started with the qualification of the flight detectors, the review of all requirements flowdowns as well as the finalizing of spacecraft interfaces.
The Martian Moons eXploration (MMX) mission led by JAXA will conduct remote sensing of both Martian moons Phobos and Deimos and in-situ observations and return samples from Phobos. A small rover will be operating on Phobos’ surface and perform scientific measurements, in particular with its Raman Spectrometer for MMX (RAX). The instrument is jointly developed by DLR with partners from Spain (INTA, University of Valladolid) and Japan (JAXA, University of Tokyo). With its more than 20 optical elements (e.g. laser, lenses, mirrors, grating, dichroic beam-splitters, spectral filters), the optical alignment and integration of this very compact Raman spectrometer was one of the biggest challenges of the instrument development at DLR. This article will cover the different steps of alignment with 1) the integration of the lenses in each individual lens group, 2) the alignment and integration of each lens group to build the spectrometer, and 3) the global alignment verification of the end-to-end instrument. The main goal was to integrate the optical elements in RAX’s mechanical housing providing maximized scientific performance. This meant for example that the detector’s sensitive surface had to be precisely placed at the focal plane surface of the imaging objective to optimize the spectral resolution, but also that the confocality of the laser output (and image on Phobos’ surface) with the spectrometer slit had to be very accurately adjusted to optimize the Signal to Noise Ratio of the Raman features. Aligning and integrating a state-of-the art Raman spectrometer in a very compact volume of less than 10x10x10 cm³ and a mass lower than 1.5 kg was challenging but successful. The different tests performed on the instrument presented here also showed the robustness of the design and demonstrated that RAX can perform excellent scientific measurements on Phobos.
Verification of thermal-mechanical-optical design for optical instruments in space exploration is highly significant due to large temperature variation and exposure to high shock and vibration levels. Such instruments must be completely robust to these harsh environments, as there are usually no options for realignment. The JAXA Martian Moons eXploration (MMX) Mission is set for launch in 2024 with main objectives to study the Martian moons, Deimos and Phobos. A rover will acquire for the first time Raman spectra of the Phobos surface using the Raman Spectrometer for MMX (RAX) developed at DLR. The Structural-Thermal-Model (STM) of RAX presented an early opportunity to evaluate the robustness of the instrument optical alignment to thermal and mechanical environments. An interferometric method implementing dummy objectives with cross hairs was developed to enable inline six-DOF measurements at critical places within the STM before development model (DM) optics were manufactured.
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