Browsing by Author "Srama, Ralf (Priv.-Doz. Dr.-Ing.)"

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Open Access
Instrument study of the Lunar Dust eXplorer (LDX) for a lunar lander mission
(2016) Li, Yanwei; Srama, Ralf (Priv.-Doz. Dr.-Ing.)
One of the highest-priority issues for a future human or robotic lunar exploration is the fine lunar dust created by meteoroid bombardment on the lunar surface with an average speed of 17 km/s. This problem should be studied in depth in order to develop an environment model for future lunar explorations. The proposed ESA lunar lander mission requires the measurement of dust transport phenomena above the lunar surface. In response to the mission requirements, an instrument design concept was developed, simulated, manufactured and tested at the Heidelberg dust accelerator facility. In contrast to former detectors, the sensor is capable to measure charged particles in a broader speed window, ranging from as low as meter per second to several kilometers per second. Furthermore, the new instrument approach is optimized for the instrument requirements of the lunar lander concept investigated by ESA. The Lunar Dust eXplorer (LDX) has a low mass of 1.2 kg and consumes a power of 1.1 W (digital electronics). The sensitive area of LDX is approximately 400 cm2. It measures the charge, speed and trajectory of individual dust particles. Meanwhile, LDX has an impact ionization target to monitor the mass of interplanetary dust and high speed ejecta. In the beginning of this study, the charge induction signals of the detector were simulated using the COULOMB software package in order to constrain the sensor accuracies. Simulations reveal trajectory uncertainties of better than 2° with an absolute position accuracy of better than 2 mm. Following simulations, a laboratory model of the LDX sensor was designed, manufactured and tested using the 2 MV Van-de-Graaff accelerator located at the Max-Planck Institute for Nuclear Physics in Heidelberg. This accelerator is a world wide unique facility to simulate hyper-velocity impacts of micron and sub-micron particles. It is currently operated by the Institute of Space System of the University of Stuttgart (IRS, Stuttgart). The experimental results additionally reveal particle primary charge uncertainties of better than ±5% and particle speed uncertainties of better than ±7%. What are the dust populations a sensor like LDX can detect on the lunar surface? How large is the contribution by secondary ejecta falling back to the surface and what is their angular distribution and speed range? To answer these questions, Autodyn 14.0/2D software was used to simulate hyper-velocity impacts of micrometeoroids bombarding the lunar surface. The initial projectiles were selected as 10 mm spheres in diameter with an average speed of 17 km/s. Furthermore, we used impact angles of 15°, 30°, 45°, 60°, 75° and 90°. In the early stage of the impact process, the projectile is coupling its energy and momentum to the target. A part of the ejecta grains created during this early stage can be captured by a sensor located on the lunar surface like e.g. the Lunar Ejecta and Meteorites (LEAM) experiment or mounted on a lander (e.g. LDX). The simulations show, that most of the detectable ejecta have low speeds (< 100 m/s1), and there are also a few grains with high speeds (> 1 km/s). The observation geometry of the sensor was investigated. Here we discuss a trade-off between a lander-mounted sensor and a surface located system. Although the LEAM data are not fully understood until today, our recent re-analysis of the data consider impact ejecta as one of the most likely sources to explain the observed event rates. Meanwhile, our studies show that a sensor mounted on the lander instead of standing on the lunar surface has more chances to measure the high-speed component of the ejecta population. The newly developed LDX sensor system is a powerful tool to study the lunar dust environment. In addition to lunar landers, smaller rover systems are also very interesting in future missions. A dust detector onboard a lunar rover would have several advantages: the measurements by the sensor can be taken at different regions of the lunar surface. Furthermore, the sensor will monitor the interaction of the rover with the lunar dust environment (plasma, electric fields, and dust). On the other hand, there are also disadvantages. The instruments onboard a rover have to maintain severe mass and data volume restrictions. Therefore we developed two further simplified designs with a lower number of electrodes and an even lower instrument mass with respect to the original LDX design. The fundamental difference between the two versions is their housing geometries. One design uses a cylindrical housing (LDX-c), and the second design has a square cross section (LDX-s). The measurement accuracies of these two detector designs are similar to LDX, but the trajectory accuracy decreases slightly by up to 2 degrees. Nevertheless, such an instrument promises, for the first time, reliable data for the properties of the lunar dust environment.
Open Access
Machine learning and Monte Carlo based data analysis methods in cosmic dust research
(2019) Albin, Thomas; Srama, Ralf (Priv.-Doz. Dr.-Ing.)
This work applies miscellaneous algorithms from the fields Machine Learning and Computational Numerics on the research field Cosmic Dust. The task is to determine the scientific and technical potential of using different methods. Here, the methods are applied on two different projects: the meteor camera system Canary Island Long-Baseline Observatory (CILBO) and the Cassini in-situ dust telescope Cosmic-Dust-Analyzer (CDA).