Showing papers by "Ralf Srama published in 2013"

Theory and experiments characterizing hypervelocity impact plasmas on biased spacecraft materials

Abstract: Space weather including solar activity and background plasma sets up spacecraft conditions that can magnify the threat from hypervelocity impacts. Hypervelocity impactors include both meteoroids, traveling between 11 and 72 km/s, and orbital debris, with typical impact speeds of 10 km/s. When an impactor encounters a spacecraft, its kinetic energy is converted over a very short timescale into energy of vaporization and ionization, resulting in a small, dense plasma. This plasma can produce radio frequency (RF) emission, causing electrical anomalies within the spacecraft. In order to study this phenomenon, we conducted ground-based experiments to study hypervelocity impact plasmas using a Van de Graaff dust accelerator. Iron projectiles ranging from 10−16 g to 10−11 g were fired at speeds of up to 70 km/s into a variety of target materials under a range of surface charging conditions representative of space weather effects. Impact plasmas associated with bare metal targets as well as spacecraft materials were studied. Plasma expansion models were developed to determine the composition and temperature of the impact plasma, shedding light on the plasma dynamics that can lead to spacecraft electrical anomalies. The dependence of these plasma properties on target material, impact speed, and surface charge was analyzed. Our work includes three major results. First, the initial temperature of the impact plasma is at least an order of magnitude lower than previously reported, providing conditions more favorable for sustained RF emission. Second, the composition of impact plasmas from glass targets, unlike that of impact plasmas from tungsten, has low dependence on impact speed, indicating a charge production mechanism that is significant down to orbital debris speeds. Finally, negative ion formation has a strong dependence on target material. These new results can inform the design and operation of spacecraft in order to mitigate future impact-related space weather anomalies and failures.

Detection of electromagnetic pulses produced by hypervelocity micro particle impact plasmas

Abstract: Hypervelocity micro particles (mass < 1 ng), including meteoroids and space debris, routinely impact spacecraft and produce plasmas that are initially dense (∼1028 m−3), but rapidly expand into the surrounding vacuum. We report the detection of radio frequency (RF) emission associated with electromagnetic pulses (EMPs) from hypervelocity impacts of micro particles in ground-based experiments using micro particles that are 15 orders of magnitude less massive than previously observed. The EMP production is a stochastic process that is influenced by plasma turbulence such that the EMP detection rate that is strongly dependent on impact speed and on the electrical charge conditions at the impact surface. In particular, impacts of the fastest micro particles occurring under spacecraft charging conditions representative of high geomagnetic activity are the most likely to produce RF emission. This new phenomenon may provide a source for unexplained RF measurements on spacecraft charged to high potentials.

The filtering of interstellar dust in the solar system

Abstract: Context. Theoretical predictions demonstrate that small ( m) interstellar grains are mostly excluded from reaching the planetary system by electromagnetic interactions in the heliopause region and in the inner heliosphere. Bigger interstellar grains have been recorded in the planetary system by dust measurements on board Ulysses and other spacecraft. It was found that the interstellar dust flux is modulated by the interplanetary magnetic field.Aims. The objective of this study is to analyze the heliospheric filtering of the interstellar dust flow through the solar system and throughout the solar cycle. In the heliosphere the dynamics of interstellar dust is governed by the gravitational pull of the Sun, by the repulsion of solar radiation, and by the deflection caused by the interaction of the charged interstellar dust (ISD) grains with the interplanetary magnetic field. These interactions are described by the parameters of the radiation pressure constant β and the charge-to-mass ratio Q /m , which depend on the particle’s size, physical properties, and composition. A previous paper studied the flow characteristics of ISD moving through the solar system were studied. In this follow-up paper, we focus on how the ISD size distribution varies during its passage through the solar system.Methods. In a parametric study of 70 different β and Q /m values, we calculated interstellar dust trajectories starting at the boundary of the heliosphere with starting times spread over a complete solar cycle of 22 years.Results. As a result we obtained the interstellar dust flux and dust speed for these times and positions and demonstrate the effects of the filtering on the dust size distributions. The size distribution of ISD observed at any time and at any position in the planetary system is strongly modified from when it entered the heliosphere. Peaks in relative flux of 10 times the original flux possibly depend on the grain size and place and time in the solar system. We did a detailed study of three cases of the flux and size distribution of interstellar grains reaching the planets Saturn, Jupiter, and the main-belt asteroid Ceres. These cases are used to get a first idea of what a dust detector or collector on a mission to these bodies might see of ISD.

Probing IMF using nanodust measurements from inside Saturn's magnetosphere

Abstract: [1] We present a new concept of monitoring the interplanetary magnetic field (IMF) by using in situ measurements of nanodust stream particles in Saturn's magnetosphere. We show that the nanodust detection pattern obtained inside the magnetosphere resembles those observed in interplanetary space and is associated with the solar wind compression regions. Our dust dynamics model reproduces the observed nanodust dynamical properties as well as the detection pattern, suggesting that the ejected stream particles can reenter Saturn's magnetosphere at certain occasions due to the dynamical influence from the time-varying IMF. This method provides information on the IMF direction and a rough estimation on the solar wind compression arrival time at Saturn. Such information can be useful for studies related to the solar wind-magnetosphere interactions, especially when the solar wind parameters are not directly available.

Application and calibration of a simple position detector for a dust accelerator

Abstract: A newly developed position sensitive detector was implemented in the beam line of the Heidelberg dust accelerator. By charge induction, the detector enables the position of a dust particle to be determined without affecting its motion. The detector consists of four pairs of parallel plates, connected to a single common charge amplifier. The charge induced on the plates varies as a function of the dust particle trajectory, producing simple, easily interpreted signals. Using a segmented target installed in the beam line for a second independent measure of the trajectory, the position detector has been calibrated, allowing the detector signal to be mapped to a dust particle position. The resulting calibration curve indicates that the detector's position accuracy is approximately 0.14 mm, based on an average SNR of 700 for dust particles passing through the centre of the detector. The minimum dust charge for reliable detection was found to be about 1.1 fC. A detector simulation was used to produce a calibration curve that confirms the experimental results.

Dust orbitrap sensor (dots) for in-situ analysis of airless planetary bodies

Abstract: C. Briois, R. Thissen, C. Engrand, K. Altwegg, A. Bouabdellah, A. Boukrara, N. Carrasco, C. Chapuis, H. Cottin, E. Grun, N. Grand, H. Henkel, S. Kempf, J.P. Lebreton, A. Makarov, F. Postberg, R. Srama, J. Schmidt, C. Szopa, L. Thirkell, G. Tobie, P. Wurz, M. Zolotov. LPC2E, 45071 Orleans Cedex, France (Christelle.Briois@cnrs-orleans.fr), IPAG, Univ. Grenoble, BP 53, 38041 Grenoble Cedex 9, France, CSNSM, Batiment 104, 91405 Orsay Campus, France, Univ. Bern, Physics Inst. Sidlerstrasse 5, 3012 Bern, Switzerland, LATMOS, 11 Blvd d’Alembert 78280 Guyancourt, France, LISA, 61 avenue du General de Gaulle, 94010 Creteil Cedex, France, Max Planck Institut fur Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany, vH&S GmbH, Schlossplatz, 68723 Schwetzingen, Germany, LASP, Colorado University, Boulder CO 80303-7814, USA, Thermo Fisher Scientific, Hanna-Kunath Str. 11, 28199 Bremen, Germany, Univ. Stuttgart, Raumfahrtzentrum Baden Wurttemberg, Pfaffenwaldring 29, 70569 Stuttgart, Germany, Univ. Oulu, Dpt Physics, PL 3000, 90014 Oulun yliopisto, Finland, LPGN, Univ. Nantes, BP 92208, 4322 Nantes Cedex 03, France.

Composition of Plasmas Formed from Debris Impacts on Spacecraft Surfaces

Abstract: The threat of electrical anomalies caused by plasma resulting from hypervelocity impacts of meteoroids and space debris has thus far not been well characterised. Here we present results from a ground-based hypervelocity impact experiment with measurements of the impact plasma formed by iron projectiles impacting on representative spacecraft materials at speeds characteristic of both meteoroids and space debris. These experiments were conducted using a Van de Graaff dust accelerator with projectiles ranging from 10−16 to 10−11 g in mass. We find that a mixture of negative ion species are produced and ejected from negatively-biased impact surfaces, and that the dependence of electron production on impact speed is weaker for surfaces with a conductive coating.