In this paper, we describe the upgrade of a small electrostatic dust accelerator located at the University of Stuttgart. The newly developed dust source, focusing lens, differential detector and linac stage were successfully installed and tested in the beam line. The input voltage range of the dust source was extended from 0–20 kV to 0–30 kV. A newly developed dust detector with two differential charge sensitive amplifiers is employed to monitor particles with speeds from several m/s to several km/s and with surface charges above 0.028 fC. The post-stage linac provides an additional acceleration ability with a total voltage of up to 120 kV. The entire system of this dust accelerator works without protection gas and without a complex high voltage terminal. The volumes to be pumped down are small and can be quickly evacuated. The new system was used to accelerate micron- and submicron-sized metal particles or coated mineral materials. Improvements in the acceleration system allow for a wider variety of dust materials and new applications.

<p class="Default"><span lang="EN-US">The surface of the </span><span lang="NL">Moon </span><span lang="EN-US">and other airless planetary bodies is usually covered by a regolith layer. The meteoroids and interplanetary dust particles bombarding such highly pulverized layer may excavate with a yield up to 1000 times of the impactor’s own mass. The excavated ejecta grains with relatively high speeds are the main components of the dust cloud around airless bodies. Faster grains with speeds exceeding the escape velocity of a planetary body contribute to the interplanetary dust environment. </span></p> <p class="Default"><span lang="EN-US">In order to understand the formation of the dust cloud around airless planetary bodies, </span><span lang="EN-US">it is necessary to deeply understand </span><span lang="EN-US">how ejecta grains are launched from regolith surfaces</span><span lang="EN-US">. We performed new oblique impact experiments on particulate targets to determine the angular and size distributions of ejecta. </span><span lang="EN-US">The spherical Aluminum projectiles of 4 mm were fired by a light gas gun at speeds of around 4.1 km/s</span><span lang="EN-US">. The targets were B<sub>4</sub>C powders with median diameters of 17 µm and the incident angles were 15</span><span lang="IT">°</span><span lang="EN-US">, 30</span><span lang="IT">°</span><span lang="EN-US">, and 45</span><span lang="IT">° </span><span lang="EN-US">to the target surface. Around the target, arrays of thin Al foils with thicknesses of 15 µm were installed, which were penetrated by high speed ejecta grains. The resulting holes were analyzed with computer vision methods. Our preliminary result is that we found (1) the sizes of major ejecta grains are comparable with median diameters of the target powder; (2) the angular distributions of ejecta varies with the incident angle of the impactor. </span></p>

<p>The return to the Moon pushed forward by space agencies as well as private companies around the world, has rekindled interest in the Lunar dust environment, which was identified as a major factor in spacecraft safety and reliability considerations during the Apollo missions. Orbiting the Moon from 2013 to 2014, the Lunar Atmosphere and Dust Environment Explorer (LADEE) gathered conclusive evidence for the existence of a permanent, asymmetric dust cloud around the Moon [1]. Micron-sized ejecta particles generated at impact of interplanetary meteoroids on the Lunar surface act as the main source of this high-altitude dust exosphere, which shows a variable density in dependence of annual meteoroid showers.</p><p>Here we report on the development of a dynamic model for the lunar ejecta dust cloud. This model simulates cloud particles in a Monte-Carlo fashion, drawing on a combination of existing engineering models and results from hypervelocity impact experiments as model inputs: To emulate the influx of meteoroids we use the Interplanetary Meteoroid Environment Model 2 (IMEM2) [2], developed under ESA contract, as well as a comet stream model based on meteor shower zenith-hourly-rates [3, 4]. To determine angular, velocity, and size distributions of ejecta particles, we resort to three different methods: (1) We use the software <em>Ansys Autodyn</em> to numerically model ejecta particles generated at hypervelocity impacts. (2) Impact experiments with a light-gas gun have been conducted at the Harbin Institute of Technology, to derive ejecta distributions generated by bigger projectiles. (3) We intend to conduct hypervelocity impact experiments with lunar soil simulant at the electrostatic dust-accelerator facility at the University of Stuttgart. The novel experiment set-up, which uses a delay-line-detector to measure micron-sized ejecta particles has recently been verified [5]. Ultimately, the simulated dust ejecta cloud will be fitted to LADEE/LDEX data. This poster-presentation gives an overview of the project and its various modules.</p><p><strong>References:</strong><br>[1] Horányi, M., et al. "A permanent, asymmetric dust cloud around the Moon." <em>Nature</em> 522.7556 (2015): 324-326.<br>[2] Soja, R. H., et al. "IMEM2: a meteoroid environment model for the inner solar system." <em>Astronomy & Astrophysics</em> 628 (2019): A109.<br>[3] Jenniskens, Peter. "Meteor stream activity I. The annual streams." <em>Astronomy and Astrophysics</em> 287 (1994): 990-1013.<br>[4] McBride, Neil. "The importance of the annual meteoroid streams to spacecraft and their detectors." <em>Advances in Space Research</em> 20.8 (1997): 1513-1516.<br>[5] Li, Yanwei, et al. "Measurement of fragments generated by hypervelocity impacts of micron-sized iron particles at grazing incidents." <em>Advances in Space Research</em> 69.6 (2022): 2629-2635.</p>

<p>Cosmic dust particles are important messengers. They contain information about their origin and their journey through space. The DESTINY<sup>+</sup> mission that launches in 2024 provides the opportunity to investigate the dust populations present at 1 AU and around the active asteroid (3200) Phaethon. For this purpose, the Destiny<sup>+</sup> Dust Analyzer (DDA) is employed. The instrument is developed under the lead of the University of Stuttgart in Germany. Its capabilities are to simultaneously analyze the dynamical and compositional properties of individual cosmic dust grains that are intersected along the mission. To gain independence from the S/C attitude a two axes pointing mechanism is developed. It provides an azimuthal range of 180° and an elevation range of 90°. The full instrument electronics is developed by the industry partner von Hoerner & Sulger GmbH in Schwetzingen, Germany while the software development takes place at the University of Stuttgart. The mass of the full instrument is ~12 kg and the power consumption is ~35 W in observation mode. The particle trajectory and grain size are determined by the trajectory sensor stage. It utilizes the fact that particles in space carry a surface charge. It consists out of a segmented plane of metal grids of which each is connected to a charge sensitive amplifier. This plane is sandwiched between two grids that are on ground potential. If a charged particle resides in between the grounded planes, it induces a mirror charge on the measurement grid segments. The incident angle, velocity and surface charge of the dust grains are reconstructed from the course and amplitude signal traces. An impact ionization time of flight mass spectrometer provides the compositional analysis of the dust grains. The sensor target is a gold surface with 300 cm² sensitive area and a field of view of 1.99 steradian. Particles collide with the sensor target with relative speeds of several km·s<sup>-1</sup>. At impact they ionize and the impact plasma is manipulated by electric fields. The cations are accelerated, reflected and focused towards an electron multiplier wich functions as an ion detector. Here the cations are detected with high temporal resolution at two sensitivity stages. This allows to identifie the presence cations in the atomic mass range of 1 – 800 u with a high dynamic range. In the relevant ion mass range of silicates, carbon and metals the mass resolution is high enough so separate the individual atomic species. As the mass spectrometer is highly sensitive to contamination the target can be heater for decontamination. A door cover protects the cleanliness of the sensor interior during launch. Additionaly to the mass spectrum the cation charge is measured by charge sensitive amplifiers at an ion grid in front of the multiplier aperture and an ion ring around it. The negative plasma charge is measured at the target. All signal channels are contiuously active and analyzed by an FPGA. A frame of the signal set is stored as soon as trigger conditions are met. This sensitive yet robust system allows to separate actual dust impacts from noise events. An uncompressed signal set from an individual impact event has a size of ~400 kbit and 2 Gbit non volatile ram is available for storage. Data processing is performed by a SAMRH71 from Microchip. Lossless and lossy compression algorithms are implemented for reducing the packet size for downlink. The talk will give an overview of the instrument functionality and design. We will present the development status and the results of first dust impact measurement will be presented, that are obtained by laboratory measurements with a dust accelerator.</p> <p> </p> <p><img src="" alt="" width="1065" height="858" /><img /></p> <p>Crossection cut through the DDA Sensor. Pointing mechanism and sensor head for measuring cosmic dust particles are depicted. A separate electronics box (not depicted) is located inside the S/C. </p>