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When electrical arcs occur in space, a plasma expands away from the arc-site, neutralizing adjacent surfaces (a current), and causing a current to be produced at the arc-site (source of neutralization current). The speed of this plasma expansion depends on the plasma species, which in turn depend on the ionizable materials near the initial electrostatic discharge (ESD) site. Based on laboratory experiments undertaken as part of the U.S. round-robin experiments on plasma propagation speed, a scenario for arc plasma propagation and arc current profiles is presented. It is found that the complex arc current profiles invariably seen in laboratory arcs are due to a multicomponent plasma, where each plasma species expands away from the arc-site supersonically and with approximately constant velocity. Apparent slowing of the arc plasma seen in high-speed video cameras is caused by the density depletion of the lightest (most rapid) plasma component first and heavier (slower) plasma components later. Electron currents onto surfaces originate at the arc-site, and the conductive arc plasma is a conduit for these currents. Sudden, simultaneous onset of arc currents at all distances from the arc-site is the result of blowoff currents, making all surfaces more positive, which then attract ambient electrons. Sudden, simultaneous cutoff of arc currents at all distances from the arc-site is the result of collapse of the plasma due to conditions at the arc-site. The ionization at the arc-site during the arc is seen to be rapidly variable, with variations on the nanosecond timescale. This model not only makes the varied plasma velocities reported in the literature understandable, but it also makes predictions about the arc radio-frequency interference (RFI), contamination produced by the arcs, and the total charge in an arc possible. Arc-site materials are suggested which, being hard to ionize and with massive ions, minimize arc currents and maximize arc current rise times. [ABSTRACT FROM AUTHOR]

The speed plasma propagates across a charged solar panel after a primary arc is one of the most important, yet poorly known, quantities in determining Electrostatic Discharge (ESD) currents for spacecraft arcing events. A review of the literature over the last two decades reveals that measured propagation velocity varies by as much as an order of magnitude. To overcome this deficiency, a round-robin set of tests was initiated with partners from industry, academia, NASA and the U.S. Air Force. This paper will provide the most recent results from the Air Force Research Laboratory testing conducted at the Spacecraft Charging and Instrument Calibration Laboratory. [ABSTRACT FROM PUBLISHER]

Proper spacecraft design and testing depend on a knowledge of the worst case environment and the number of arcs to be endured during the spacecraft lifetime. In this paper, we define the criteria to be used to specify the worst case geosynchronous earth orbit (GEO) charging environment (plasma density and temperature), including the physical constraints on particle and magnetic field energy densities and the relative importance of frame charging and differential charging. A previous estimate of the frequency of arcing (found in the literature and incorporated into an International Standards Organization standard) and the consequent total number of arcs to be encountered in a GEO satellite lifetime are found to be incorrect because they were based on environmental measurements using a faulty algorithm to determine spacecraft charging and plasma density. Using more accurate estimates of the frequency of GEO plasma densities and temperatures, we arrive at a much lower estimate of the total number of arcs during a GEO satellite lifetime. Finally, the worst case GEO charging environment seen to date is determined from Nascap-2k simulations. Our estimates of worst case charging environments and arc frequencies may be more confidently used by GEO spacecraft designers and test engineers. [ABSTRACT FROM PUBLISHER]

Electrostatic discharges on the spacecraft solar array surfaces have been studied for over 40 years. Multiple tests in many laboratories have been performed to reveal the mechanisms of current pulse formation, to determine plasma expansion speed and dimensions of neutralized surface area, and to define the parameters of the electric circuits to be able to adequately simulate space discharges in plasma chambers. Initially, a thorough analysis of all the available experimental data is performed to achieve progress in the creation of a satisfactory theoretical description of pulse wave forms and surface neutralization processes. It is shown that there are two main reasons for the significant variations observed in pulse wave forms, durations, and amplitudes; differences in test arrangements and pure statistical variations caused by the random nature of arc inception and development. Then, the theoretical model of flashover current pulse formation due to coverglass charge neutralization at the plasma perimeter is carefully considered and confronted with existing experimental data. It is found that this theory contains some appropriate elements but cannot be applied for quantitative explanation of pulse wave forms. The comparison of theoretical results and experimental data clearly shows that there is no (and there cannot be) such thing as a standard pulse. To estimate the possibility of detrimental effects from primary arcs, these events must be studied and analyzed statistically. [ABSTRACT FROM PUBLISHER]

Plasma ground-testing results, obtained at the John H. Glenn Research Center National Plasma Interaction Facility, are presented for a number of thin-film photovoltaic cells. The cells represent a mix of promising new technologies identified by the Air Force Research Laboratory under the Space Science Technology Experiment (SSTE-4) Program. The current ground-testing efforts are aimed at characterizing both the performance and survivability of thin-film technologies in the harsh Low Earth Orbit space environment where they are intended to be flown. Measurements of parasitic currents and arc threshold voltages were performed in situ under strictly controlled charging conditions for both amorphous silicon (a-Si) and copper indium gallium selenide cells. Surface flashing on the large-area a-Si cells revealed that microdischarges in the dielectric surface do not appear to cause any apparent degradation to the cells. Catastrophic arc testing between adjacent cells resulted in no sustained arcs. Similar catastrophic arc tests between adjacent strings resulted in self-extinguished nonsustained arc extensions on time scales of approximately 100 μs in length. All cell efficiency measurements were performed in the Solar Cell Calibration Laboratory prior to plasma testing and then once again after the completion of the plasma tests. [ABSTRACT FROM AUTHOR]

Tests of arcing and current collection in simulated-space-plasma conditions have been performed at the National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) in Cleveland, OH, for over 30 years and at the Marshall Space Flight Center (MSFC) in Huntsville, AL, for almost as long. During this period, proper test conditions for an accurate and meaningful space simulation have been worked out, comparisons with actual space performance in spaceflight tests and with real operational satellites have been made, and NASA has achieved the authors' own internal standards for test protocols. It is the purpose of this paper to communicate the test conditions, test procedures, and types of analysis used at the NASA GRC and MSFC to the space environmental testing community at large, to help with international space-plasma arcing-testing standardization. Discussed herein are the neutral gas conditions, plasma densities and uniformity, vacuum chamber sizes, sample sizes and Debye lengths, biasing samples versus self-generated voltages, floating samples versus grounded samples, test electrical conditions, arc detection, preventing sustained discharges during testing, real samples versus idealized samples, validity of low Earth orbit tests for geosynchronous Earth orbit samples, extracting arc threshold information from an arc rate versus voltage tests, snapover, current collection and glows at the positive sample bias, Kapton pyrolysis, thresholds for trigger arcs, sustained arcs, dielectric breakdown and Paschen discharge, tether arcing and testing in very dense plasmas (i.e., thruster plumes), arc mitigation strategies, charging mitigation strategies, models, and analysis of test results. Finally, the necessity of testing will be emphasized, not to the exclusion of modeling, but as part of a complete strategy for determining when and if arcs will occur, and preventing them from occurring in space. [ABSTRACT FROM AUTHOR]