R. Srama | Universität Stuttgart (original) (raw)

Papers by R. Srama

The future exploration of the lunar surface by an ESA lander requires the measurement of dust tra... more The future exploration of the lunar surface by an ESA lander requires the measurement of dust transport phenomena above the surface. Therefore an instrument study investigates the properties of a dust sensor (LDX) with low mass which is based on charge induction. In this work, we used simulation software Coulomb V91 to study the possible charge signals for the dust detector-LDX. Lunar Dust eXplorer (LDX) is a hybrid trajectory sensor, with two instruments, one is used for the detection of lunar dust rising from lunar surface and the other one is used for the dust transmitting through horizontal direction of lunar surface. A dust detector landing on lunar surface supports a direct way to study this process. The Coulomb V91 software was used as a tool to simulate the induced charge signals, when a charged ejecta particle flies through LDX grid segments and wires. Grain trajectories close to the wall and to segment edges have a strong influence to the signal shapes. The wires diameters...

Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 2014

ABSTRACT The German X-ray telescope eROSITA will perform the first imaging all-sky survey in the ... more ABSTRACT The German X-ray telescope eROSITA will perform the first imaging all-sky survey in the medium energy range up to 10 keV with unprecedented spectral and angular resolution. The launch of eROSITA onboard of the Russian Spectrum- Röntgen-Gamma satellite into an orbit around the L-2 lagrangian point is foreseen in 2016. Even tough the L-2 space environment can be considered free of orbital debris, the presence of extraterrestrial meteoroids in the interplanetary space implies a certain hazard for the eROSITA pnCCDs, as experienced by both pn and MOS cameras onboard XMM-Newton. In this paper we address this question and investigate the response of the optical blocking filter to hypervelocity impacts.

The Cosmic Dust Analyzer (CDA) onboard the Cassini mission measures the properties of micron size... more The Cosmic Dust Analyzer (CDA) onboard the Cassini mission measures the properties of micron sized dust particles in the environment of Saturn. Since its arrival at Saturn in July 2004, the CDA detector recorded many thousand dust impacts within the E ring of Saturn. Data analysis revealed enhanced dust densities until a radial distance of at least 16 Saturn radii. The dust densities and the mass distribution of the ring particles is investigated. Furthermore, compositional measurements indicate a clear dominance of water ice particles in the size range between 0.5 and 2 micro meter. The discovery of the extended E ring changes the former understanding and modeling based on remote sensing observations.

Planetary and Space Science, 2009

We discuss issues involved with interpreting time-of-flight mass spectra (TOFMS) obtained by the ... more We discuss issues involved with interpreting time-of-flight mass spectra (TOFMS) obtained by the Chemical Analyser subsystem of the Cassini Cosmic Dust Analyser (CDA). We use an in-house ion dynamics code specifically written for CDA which helps us to understand and constrain the initial impact plasma ion kinetic energy and angular distributions. We also present some typical results obtained from within the Saturnian system. We find that particles predominantly consist of water ice (manifesting itself in the TOFMS as hydronium ions, with varying numbers of water molecules attached) and minor silicate impurities. Some ammonia may also be present.

Planetary and Space Science, 2015

One of the highest-priority issues for a future human or robotic lunar exploration is the lunar d... more One of the highest-priority issues for a future human or robotic lunar exploration is the lunar dust. This problem should be studied in depth in order to develop an environment model for a future lunar exploration. The impact ejecta of interplanetary meteoroids is one of the source mechanics of the lunar dust environment. A dust detector placed on the lunar surface is exposed to strong variations in the impact ejecta environment. The purpose of this article is a study of the speed and trajectory information of ejecta created by micrometeoroid impacts. Auto-dyn14.0/2D software was used to simulate the impacting by micrometeoroids bombarding the lunar surface. The projectiles were selected as 10 µm spheres in diameter with the speed of 17 km•s −1. We used impact angles of 30 • , 45 • , 60 • and 90 •. A part of impact ejecta grains created in the early stage of impact process can be captured by a sensor placed on the lunar surface (e.g. Lunar Ejecta and Meteorites (LEAM) experiment) or mounted on a lunar lander (e.g. Lunar Dust eXplorer (LDX)). Most of the detectable ejecta grains have very-low-speeds (< 100 m•s −1) together with a few of high-speed ejecta grains (> 1 km•s −1). Comparing with the most recently analysis of LEAM data, the impact ejecta grains are considered as one of the most possible sources for the recorded events. Furthermore, a sensor mounted on a lander instead of directly placed on the lunar surface has more chances to measure high-speed ejecta. A new developed instrument, such as LDX, will be a powerful tool to study the lunar dust environment.

Priorities are described for research on trans-Neptunian Objects (TNOs), a recently-discovered (t... more Priorities are described for research on trans-Neptunian Objects (TNOs), a recently-discovered (thereby excluding Pluto and Charon) population of small, outer solar system objects with important implications for the early history of the solar system. We conclude that we must discover and obtain accurate orbits for an unbiased sample of ~5000 TNOs over the next decade and a significant fraction of these objects must be targeted for more detailed physical observations. A broad range of complementary theoretical and laboratory studies are also needed, and we must work towards direct spacecraft exploration of TNOs as soon as possible.

Planetary and Space Science, 2006

Meteoritics & Planetary Science, 2011

The 'Interplanetary Meteoroid Environment for eXploration' (IMEX) project, funded by the European... more The 'Interplanetary Meteoroid Environment for eXploration' (IMEX) project, funded by the European Space Agency (ESA), aims to characterize dust trails and streams produced by comets in the inner solar system. We are therefore developing a meteoroid stream model that consists of a large database of cometary streams from all known comets in the inner solar system. This model will be able to predict meteor showers from most known comets, that can be observed anywhere in the inner solar system, at any time 1980-2080. This is relevant for investigating meteor showers on the Earth, on other planets, or at spacecraft locations. Such assessment of the dust impact hazard to spacecraft is particularly important in the context of human exploration of the solar system.

The future exploration of the lunar surface by an ESA lander requires the measurement of dust tra... more The future exploration of the lunar surface by an ESA lander requires the measurement of dust transport phenomena above the surface. Therefore an instrument study investigates the properties of a dust sensor (LDX) with low mass which is based on charge induction. In this work, we used simulation software Coulomb V91 to study the possible charge signals for the dust detector-LDX. Lunar Dust eXplorer (LDX) is a hybrid trajectory sensor, with two instruments, one is used for the detection of lunar dust rising from lunar surface and the other one is used for the dust transmitting through horizontal direction of lunar surface. A dust detector landing on lunar surface supports a direct way to study this process. The Coulomb V91 software was used as a tool to simulate the induced charge signals, when a charged ejecta particle flies through LDX grid segments and wires. Grain trajectories close to the wall and to segment edges have a strong influence to the signal shapes. The wires diameters...

Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 2014

ABSTRACT The German X-ray telescope eROSITA will perform the first imaging all-sky survey in the ... more ABSTRACT The German X-ray telescope eROSITA will perform the first imaging all-sky survey in the medium energy range up to 10 keV with unprecedented spectral and angular resolution. The launch of eROSITA onboard of the Russian Spectrum- Röntgen-Gamma satellite into an orbit around the L-2 lagrangian point is foreseen in 2016. Even tough the L-2 space environment can be considered free of orbital debris, the presence of extraterrestrial meteoroids in the interplanetary space implies a certain hazard for the eROSITA pnCCDs, as experienced by both pn and MOS cameras onboard XMM-Newton. In this paper we address this question and investigate the response of the optical blocking filter to hypervelocity impacts.

The Cosmic Dust Analyzer (CDA) onboard the Cassini mission measures the properties of micron size... more The Cosmic Dust Analyzer (CDA) onboard the Cassini mission measures the properties of micron sized dust particles in the environment of Saturn. Since its arrival at Saturn in July 2004, the CDA detector recorded many thousand dust impacts within the E ring of Saturn. Data analysis revealed enhanced dust densities until a radial distance of at least 16 Saturn radii. The dust densities and the mass distribution of the ring particles is investigated. Furthermore, compositional measurements indicate a clear dominance of water ice particles in the size range between 0.5 and 2 micro meter. The discovery of the extended E ring changes the former understanding and modeling based on remote sensing observations.

Planetary and Space Science, 2009

We discuss issues involved with interpreting time-of-flight mass spectra (TOFMS) obtained by the ... more We discuss issues involved with interpreting time-of-flight mass spectra (TOFMS) obtained by the Chemical Analyser subsystem of the Cassini Cosmic Dust Analyser (CDA). We use an in-house ion dynamics code specifically written for CDA which helps us to understand and constrain the initial impact plasma ion kinetic energy and angular distributions. We also present some typical results obtained from within the Saturnian system. We find that particles predominantly consist of water ice (manifesting itself in the TOFMS as hydronium ions, with varying numbers of water molecules attached) and minor silicate impurities. Some ammonia may also be present.

Planetary and Space Science, 2015

One of the highest-priority issues for a future human or robotic lunar exploration is the lunar d... more One of the highest-priority issues for a future human or robotic lunar exploration is the lunar dust. This problem should be studied in depth in order to develop an environment model for a future lunar exploration. The impact ejecta of interplanetary meteoroids is one of the source mechanics of the lunar dust environment. A dust detector placed on the lunar surface is exposed to strong variations in the impact ejecta environment. The purpose of this article is a study of the speed and trajectory information of ejecta created by micrometeoroid impacts. Auto-dyn14.0/2D software was used to simulate the impacting by micrometeoroids bombarding the lunar surface. The projectiles were selected as 10 µm spheres in diameter with the speed of 17 km•s −1. We used impact angles of 30 • , 45 • , 60 • and 90 •. A part of impact ejecta grains created in the early stage of impact process can be captured by a sensor placed on the lunar surface (e.g. Lunar Ejecta and Meteorites (LEAM) experiment) or mounted on a lunar lander (e.g. Lunar Dust eXplorer (LDX)). Most of the detectable ejecta grains have very-low-speeds (< 100 m•s −1) together with a few of high-speed ejecta grains (> 1 km•s −1). Comparing with the most recently analysis of LEAM data, the impact ejecta grains are considered as one of the most possible sources for the recorded events. Furthermore, a sensor mounted on a lander instead of directly placed on the lunar surface has more chances to measure high-speed ejecta. A new developed instrument, such as LDX, will be a powerful tool to study the lunar dust environment.

Priorities are described for research on trans-Neptunian Objects (TNOs), a recently-discovered (t... more Priorities are described for research on trans-Neptunian Objects (TNOs), a recently-discovered (thereby excluding Pluto and Charon) population of small, outer solar system objects with important implications for the early history of the solar system. We conclude that we must discover and obtain accurate orbits for an unbiased sample of ~5000 TNOs over the next decade and a significant fraction of these objects must be targeted for more detailed physical observations. A broad range of complementary theoretical and laboratory studies are also needed, and we must work towards direct spacecraft exploration of TNOs as soon as possible.

Planetary and Space Science, 2006

Meteoritics & Planetary Science, 2011

The 'Interplanetary Meteoroid Environment for eXploration' (IMEX) project, funded by the European... more The 'Interplanetary Meteoroid Environment for eXploration' (IMEX) project, funded by the European Space Agency (ESA), aims to characterize dust trails and streams produced by comets in the inner solar system. We are therefore developing a meteoroid stream model that consists of a large database of cometary streams from all known comets in the inner solar system. This model will be able to predict meteor showers from most known comets, that can be observed anywhere in the inner solar system, at any time 1980-2080. This is relevant for investigating meteor showers on the Earth, on other planets, or at spacecraft locations. Such assessment of the dust impact hazard to spacecraft is particularly important in the context of human exploration of the solar system.