The first NASA spacecraft to visit and explore planet Venus since the 1990s will be the Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy mission (VERITAS) orbiter. The Venus Emissivity Mapper (VEM) onboard the spacecraft is designed for surface mapping of Venus within dedicated atmospheric spectral windows. The instrument will provide global coverage for the detection of thermal emissions like volcanic activity, surface rock composition, water abundance, cloud formation and their dynamics by observing 14 narrow filter bands in the near-infrared to short-wave infrared (NIR, SWIR) range of 790 nm to 1510 nm. An almost identical instrument will be part of ESA’s recently announced EnVision mission to Venus, the VenSpec-M in the Venus Spectroscopy Suite (VenSpec). The utilized photodetector for both missions will be an InGaAs type imaging sensor with integrated thermoelectric (TE) cooling, comprising a 640x512 pixel array with 20 μm pixel pitch.
In general, a space environmental qualification of electronic devices combines its susceptibility to radiation induced single event effects (SEE) and the evaluation of permanent degradation effects due to total ionizing dose (TID) and displacement damage dose (DDD). Following a successful qualification test with heavy-ions focusing on SEE, our imaging sensor was subject to a proton irradiation test campaign at Helmholtz-Zentrum Berlin (HZB) for combined TID and DDD testing. To track the sensor evolution, we subdivided the proton fluence into 10 irradiation steps with intermediate measurements. The collected data provide information on the evolution of dark current, light sensitivity and pixels showing randomtelegraph- noise (RTN) on the sensor during a 5-year mission.
We report on the current Venus Emissivity Mapper (VEM) instrument design and development status onboard NASAs Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy (VERITAS) and ESAs EnVision orbiters. The VEM instrument is a push broom multispectral imager that comprises an optical system based on a sophisticated filter assembly with 14 spectral bands and an InGaAs detector with integrated thermoelectric cooler. A turn window mechanism and a two-staged baffle in front of the optics protect the instrument against contamination and straylight. The instruments nominal mass is approximately 6 kg. VEM opens the path for mapping Venus surface emission with a global coverage of >70%.
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.
KEYWORDS: Microbolometers, Photodiodes, Spectral response, Dark current, Signal to noise ratio, Light sources, Data acquisition, Collimators, Quantum sensors, CMOS sensors
We report on the design of a new laboratory setup for testing the performance of optical and thermal sensors at temperatures ranging from 50 K to 350 K and pressures ranging from ambient atmospheric pressures down to 10-5 mbar. The system will be built around a closed-cycle cooled cryostat which houses the device under test. Optical stimuli will be provided by a calibrated selectable light source which provides collimated light from an integrating sphere or a cavity blackbody. Bandpass filters as well as imaging targets can be selected for determining the spectral response and modular transfer function. Data acquisition from the device under test will be accomplished using an automated test bench based on a custom-made FPGA interface adaption board.
The Venus Emissivity Mapper (VEM) as part of NASAs Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy mission (VERITAS) is designed for mapping the surface of Venus within dedicated atmospheric spectral windows. The instrument will provide global coverage for detection of thermal emissions like volcanic activity, surface rock composition, water abundance and cloud formation as well as dynamics by observing 15 narrow filter bands in the near infrared to short wavelength infrared (NIR, SWIR) range of 862 nm to 1510 nm. An almost identical instrument will be part of ESAs EnVision mission to Venus, the VenSpec-M in the Venus Spectroscopy Suite (VenSpec). The utilized photodetector is an InGaAs type imaging sensor with integrated thermoelectric (TE) cooling. It comprises a 640x512 pixel array with 20 μm pixel pitch. Following the mission requirements we irradiated the detector with a set of ions of various stopping powers and range distributions from lower energy Argon (Ar) to higher energy Xenon (Xe). Therefore, exploiting the mentioned ions and proper tilt angles during irradiation, our data covers a Linear Energy Transfer (LET) range of 7 to 75 MeVcm2/mg which fulfills NASA/JPL led space qualification standards (up to 75 MeVcm2/mg) as well as ESA space qualification standards (up to 60 MeVcm2/mg) for heavy-ion irradiation. Our electrical setup consists of a dedicated over-current protection detecting high-current states occurring during irradiation steps and immediate power cycling to prevent physical damage of the device. From the event rates seen during the test we calculated the specific cross-sections and therefore can estimate the expected event rates at Venus during the mission. The detector showed saturated cross-sections below 1E-3 cm2 at 10°C with acceptable event rates for the highest LETs and our applications.
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.
K. Enya, M. Kobayashi, K. Ishibashi, S. Kobayashi, N. Namiki, H. Araki, S. Tazawa, H. Noda, S. Oshigami, S. Kashima, M. Utsunomiya, J. Kimura, K. Touhara, T. Yamawaki, S. Iwamura, N. Fujishiro, Y. Matsumoto, T. Iida, H. Nakagawa, H. Imai, O. Kirino, C. Hatakeyama, T. Yokozawa, Y. Sato, K. Kojima, N. Matsui, K. Tanimoto, M. Fujii, C. Althaus, S. Del Togno, J. Jänchen, B. Borgs, T. Behnke, H. G. Lötzke, R. Kallenbach, K. Lingenauber, H. Hussmann
The Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency to be launched in 2022 will provide an opportunity for a dedicated exploration of the Jovian system including its icy moons. The Ganymede Laser Altimeter (GALA) has been selected as one of the ten payloads of JUICE. GALA will enable unique studies of the topography and shape, tidal and rotational state, and geology of primarily Ganymede but also Europa and Callisto. The GALA project is an ongoing international collaboration led by Germany, together with Switzerland, Spain, and Japan. This paper presents the optical and mechanical design of the focal plane receiver, the Japanese part of GALA.
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