Showing papers by "Ralf Srama published in 2006"
TL;DR: During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite; this asymmetric signature is consistent with a locally enhanced dust production in the south polar region of Encesladus.
Abstract: During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite. The dust impact rate peaked about 1 minute before the closest approach of the spacecraft to the moon. This asymmetric signature is consistent with a locally enhanced dust production in the south polar region of Enceladus. Other Cassini experiments revealed evidence for geophysical activities near Enceladus' south pole: a high surface temperature and a release of water gas. Production or release of dust particles related to these processes may provide the dominant source of Saturn's E ring.
306 citations
TL;DR: In this article, the electrostatic potential of E ring particles was measured using the charge-sensitive grid system of the cosmic dust analyser (CDA) on the Cassini spacecraft, which allows an in situ determination of the charge of grains bigger than 2.
82 citations
TL;DR: In this paper, the mass spectra of jovian stream particles were used to determine the chemical composition of particles, and the results imply that the vast majority (>95%) of the observed stream particles originate from the volcanic active jovians satellite Io from where they are sprinkled out far into the Solar System.
68 citations
TL;DR: In this paper, polypyrrole (PPy) has been deposited from aqueous solution onto submicrometer-sized sulfur-rich poly[bis(4-vinylthiophenyl)sulfide] (PMPV) latex particles.
Abstract: Polypyrrole (PPy) has been deposited from aqueous solution onto submicrometer-sized sulfur-rich poly[bis(4-vinylthiophenyl)sulfide] (PMPV) latex particles. The PMPV seed particles and resulting composite particles were extensively characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, FT-IR spectroscopy, helium pycnometry, Raman spectroscopy, and electrical conductivity measurements. Four-point probe measurements on pressed pellets indicate conductivities of around 6 × 10-5 S cm-1 for a polypyrrole loading of approximately 11.5%. This suggests a somewhat patchy, nonuniform polypyrrole overlayer, which is consistent with our Raman spectroscopy studies. Despite their relatively low conductivities, these polypyrrole-coated PMPV latexes can be accelerated up to hypervelocities (>20 km s-1) using a high voltage (2 MV) van de Graaf instrument. In view of their high sulfur contents (ca. 28%), these new electrically conductive latexes are expected to be interesting synthetic mimics fo...
53 citations
Max Planck Society1, California Institute of Technology2, Jet Propulsion Laboratory3, University of Chicago4, Open University5, Rutherford Appleton Laboratory6, University of Tromsø7, University of Colorado Boulder8, Technische Universität München9, European Space Research and Technology Centre10, University of Potsdam11, University of Hawaii12
TL;DR: In this paper, the authors focus on the analysis of impact rates, which were strongly variable primarily due to changes of the spacecraft pointing and the Cosmic Dust Analyser (CDA) data within Titan's orbit.
49 citations
TL;DR: In this paper, a novel dust telescope is developed based on experience with current space dust instruments, which is a combination of a dust trajectory sensor for the identification and an analyzer for the elemental composition of the dust.
Abstract: There are different types of dust particles in interplanetary space, such as dust from comets and asteroids, and interstellar grains traversing the solar system. Based on experience with current space dust instruments, a novel dust telescope is being developed. A dust telescope is a combination of a dust trajectory sensor for the identification and an analyzer for the elemental composition of the dust. Dust particles’ trajectories are determined by the measurement of the electric signals that are induced when a charged grain flies through a position-sensitive electrode system. The objective of the trajectory sensor is to measure dust charges in the range 10−16–10−13 C and dust speeds in the range 6–100 km/s. First tests with a laboratory setup have been performed. The chemical analyzer will have an impact area of 0.1 m2. It consists of a target with an acceleration grid and a single-stage reflectron for energy focusing, and a central ion detector. Results from SIMION simulations show that a mass resolution of M/ΔM>150 can be obtained.
33 citations
TL;DR: The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse (i = 79 degrees, perihelion distance 1.3 AU, aphelia distance 5.4 AU) since it encountered Jupiter in 1992 as discussed by the authors.
32 citations
TL;DR: Horanyi et al. as discussed by the authors presented data from the Galileo dust instrument for the period January 1997-December 1999 when the spacecraft completed 21 revolutions about Jupiter, in which data were obtained as high resolution real-time science data or recorded data during 449 days (representing 41% of the entire period).
20 citations
TL;DR: In this paper, the authors present a mission scenario based on the SMART 1 mission, where the Dust Telescope on-board DUNE-eXpress consists of two large area mass analyzer (LAMA) instrument modules and four dust Trajectory Sensors with a total weight of 60 kg.
13 citations
TL;DR: In this paper, a simulation of ion behavior within Cassini's cosmic dust analyser (CDA) instrument, using an inhouse ion dynamics code, is presented. And the results show that the isotropic emission of ions from the impact plasma successfully reproduces features seen in flight spectra and that the emitted ions have a higher range of energies than previously reported in some studies.
13 citations
01 Mar 2006
Abstract: INTERSTELLAR DUST COLLECTION. T. Stephan, A. L. Butterworth, C. J. Snead, R. Srama, and A. J. Westphal, Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany (stephan@uni-muenster.de), Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA 94720, USA, Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.