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Space domain awareness (SDA) is becoming more important with a constantly increasing number of artificial objects in space. Astronomical reflectance spectroscopy (ARS) is a promising technique employed for remote characterization of space objects. In geosynchronous earth orbit (GEO), the chemical characteristics of a material change continuously, as it is exposed to the harsh radiation environment of several damaging species (with electrons being the primary damaging species in terms of energy deposition). These chemical modifications alter the light absorbed by and reflected from the object at certain wavelengths, resulting in a concomitant change of the measured object’s brightness and color index. By understanding the evolution of the color index of a material as a function of time on orbit, ARS can become a powerful tool for remote characterization of space objects as well as anomaly characterization and resolution. In this study, we investigate the effect of a space-simulated environment represented by high-energy (100 keV) electrons on the evolution of optical properties of several spacecraft-relevant polymer materials. [ABSTRACT FROM AUTHOR]

The harsh space environment at geosynchronous orbit (GEO) induces differential charging of spacecraft surfaces due to simultaneous fluxes of electrons with a wide distribution of energies onto, into, and through spacecraft surface materials. Thus, satellite surfaces can charge thousands of volts with respect to each other, whereas entire satellites can charge tens of thousands of volts negative relative to their surrounding space plasma. The ensuing electric fields can cause local discharges (arcs) from one part of the spacecraft to another, endangering the normal operation of the satellite. Furthermore, solar cell coverglass contamination induced by the high rate of arcing is sufficient to produce the ~1.5%/year power loss in excess of radiation damage that has been observed on global positioning system (GPS) satellites. This work focuses on evaluation of a GEO space weather effect on material properties caused by irradiating different types of commonly used space solar cell coverglasses (CMX, fused silica, and Corning 0214) with >90-keV electron radiation. [ABSTRACT FROM AUTHOR]

The Global Positioning System (GPS) satellites arc into the space environment. Evidence for this consists of undispersed impulsive radio frequency signals are shown in the dual-frequency RF receivers, that are on-board all GPS satellites, with high rates that track the charging electron environment, detection of appropriate amplitude short-timescale pulses from GPS satellites at 327 and 430 MHz with the Arecibo 305-m Gordon radiotelescope that do not appear in off-source scans, and arcing on laboratory GPS-like solar arrays at voltages similar to those inferred from GPS arc thresholds. In addition, GPS satellites (up to the Block IIRM) have power degradation (in excess of that expected from radiation) of about 1.5% per year. This degradation is primarily in the short-circuit current, consistent with contamination on the solar array cover glasses, which was detected by a thermal monitor on one GPS satellite solar array, and to be consistent with the power degradation observed on a highly arced GPS-like laboratory solar array if extrapolated to GPS undispersed event rates. The GPS arc rates required for solar array contamination and consistent with the onboard observed event rates are very high, in fact, higher than the rates measured previously on SCATHA, CTS, and other satellites. It is conjectured that the effects of these arcs on satellite power systems have been routinely prevented by highly filtering the power system and antenna response, that most satellites have had no way to detect arcing, and that most power losses up to the present time have been ascribed to radiation damage. Results of new optical and radio-frequency radio frequency observations of satellite arcing are discussed, as well as laboratory measurements confirming the high arc rates and their consequences. [ABSTRACT FROM AUTHOR]

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]

Global positioning system (GPS) satellites are strongly suspected to arc into the space environment. Arcing on spacecraft due to differential charging can be blamed for a host of operational anomalies resulting in the loss of billions of dollars and productivity. In addition to anomalous behavior on spacecraft, arcing can be accused of an otherwise unexplained degradation in solar power production of GPS satellites while on orbit. In the study presented here, it will be shown that arcs on a GPS-representative solar array coupon under representative medium earth orbit/geosynchronous earth orbit (MEO/GEO)-like conditions result in contamination of solar panel coverglasses. This finding supports the argument that arc-induced contamination is a prime suspect in explaining the mysterious excess power loss of GPS satellites on orbit. Further, optical mapping suggests that this arcing occurs primarily at the edges of the sample panel where silicone adhesive with glass microspheres was exposed. X-ray photoelectron spectroscopy (XPS) reveals that the concentration of Si near the arc sites is increased, suggesting that the adhesive is ionized during the electrostatic discharge and coats the surface of the solar panel, resulting in reduced optical transmission through the coverglass and therefore reducing power production. X-ray depth profiling suggests that the silicon detected is due to surface contamination, and electrostatic simulations indicate that glass microspheres intended to reduce adhesive mass and produce a uniform bond-line may be exacerbating the arcing problem. [ABSTRACT FROM AUTHOR]

Low-density polyethylene (LDPE) is a nonpolar polymer commonly used as an insulating material. Although its applications in the spacecraft industry are limited, LDPE is widely utilized as a model system to study electron transport through disordered insulating materials under simulated space weather conditions. The charge transport models developed using this system may then be extended to more commonly used spacecraft materials such as polyimides. Several proposed charge transport models share high complexity and many free fitting parameters. For better estimation of initial values of these free parameters, the correlation between charge transport and its chemical origins should be made. Whenever possible, experimental measurements should be used as initial values for each of the free fitting parameters to improve model accuracy. In this paper, we studied alterations of the chemical properties of LDPE after irradiation by high-energy (100 keV) electrons using Fourier transform infrared spectroscopy (FTIR) and bulk conductivity measurements. Moreover, we utilized a quadrupole mass spectrometer (QMS) to identify the ablated species released from the solid during irradiation. These measurements offer insight into the structural and chemical damages of the material. Results of the performed analysis are correlated with the underlying chemical changes that occur in LDPE during irradiation. [ABSTRACT FROM AUTHOR]

The processes of electrical charge accumulation and dissipation in dielectric materials are critical to spacecraft construction and operational anomaly resolution. Electrical conductivity, and therefore surface potential, of radiation-damaged materials undergoes unpredicted changes while on orbit. The space environment causes fundamental modifications in the chemical structure of spacecraft materials by breaking intermolecular bonds and creating free radicals that act as space charge traps. Over time, free radicals react with each other and the material recovers. The rates of free radical formation and loss determine the dynamics of the conductivity of spacecraft materials. Lack of knowledge about dynamic aging is a major impediment to accurate modeling of spacecraft behavior over its mission life. This paper presents an investigation of the chemical and physical properties of polyimide (PI) films during and after irradiation with high-energy (90 keV) electrons. The constant voltage method was utilized to monitor material conductivity during the recovery process. To quantify the concentration of free radicals within the irradiated material, the electron paramagnetic resonance technique was used. Changes in the infrared (IR) absorption profile of irradiated materials during the recovery process were identified using the directional-hemispherical reflectance technique coupled with the Fourier transform IR spectroscopy. This physical/chemical collaboration allowed correlation of chemical changes in PI with the dynamic nature of spacecraft material aging. [ABSTRACT FROM PUBLISHER]

We present here an investigation of the arcing voltage threshold for GPS-like arrays performed in the Spacecraft Charging and Instrument Calibration Laboratory at the Air Force Research Laboratory’s Battlespace Environment Laboratory at Kirtland Air Force Base, New Mexico, USA. Our simulations were done under GPS-like plasma environments in a vacuum-plasma chamber. The arc voltage threshold found is compared with that predicted from the Los Alamos National Laboratory (LANL), detectors, and the question of to what degree were the indium tin oxide-coated cells on GPS properly grounded is discussed. It is shown through the current–voltage testing of the arrays pre- and postarcing that the anomalous power degradation seen on GPS satellites on orbit can be completely accounted for by arcing at the anomalous event rates seen by LANL radio frequency detectors onboard. Implications for arcing and contamination mitigation on future GPS satellites are presented. [ABSTRACT FROM PUBLISHER]

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]

A recent space weather headline has cast doubt in the minds of some as to whether space weather is the source of spacecraft anomalies, and thus, whether it is important in the design and operation of critical situational awareness, communications, and positioning systems. In this paper, we reiterate the evidence for the importance of space weather, its role in producing spacecraft and ground anomalies, and the threat it poses to critical systems. In addition, we report new studies broken down by anomaly types and suggest the sources of the anomalies (surface charging or interior charging). Finally, we suggest spacecraft charging and ground effects mitigation strategies for design and operations of systems critical to our modern civilization. [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]

The USAF Communication/Navigation Outage Forecast System satellite, launched into an eccentric low earth orbit (401 km perigee by 867 km apogee) of 13^\circ inclination on April 16, 2008, has a set of dc electric field probes that constitute part of the Vector Electric Field Investigation (VEFI). In order to obtain the ambient electric field, the v\times B component of electric field must be subtracted from the VEFI measurements. After this subtraction and the subtraction of the ambient dc electric components, a residual dc offset directed toward the spacecraft wake is still observed, which varies somewhat within an orbit and on longer timescales. One of the interesting features of these offsets is that when the satellite is occasionally rotated, the offsets are reset to their baseline values, only to come back within a month or so. Various hypotheses have been proposed to explain the residual dc offsets. In this paper, we explore the possibilities that either the influence of the spacecraft wake on the sensors or that modified surface layers on the probe surfaces are producing the offsets. Nascap-2k and EWB models are used to show the various influences of the wake and of surface materials. Finally, a hypothesis is produced that quantitatively explains many of the salient features of the offsets. The feasibility of using dc electric field probes in space is reaffirmed. Recommendations for probe construction on future spacecraft to ameliorate spurious effects are presented. [ABSTRACT FROM PUBLISHER]

The first preliminary results are reported from the U.S. Round-Robin Test on Plasma Expansion Speed. The tests were performed at the NASA Glenn Research Center on two coupons (six strings) of International Space Station (ISS) solar cell arrays, with a separate small array to obtain arcs (because it is so difficult to get ISS arrays to arc). ISS arrays were used because they have no exposed interconnects to act as bare current collectors and confuse the experimental results. The preconstructed ISS strings were laid out approximately parallel to the plasma expansion velocity to allow for the best test of the simple plasma expansion front current waveform model. Several Langmuir probes were arranged above and to the sides of the sample to allow for measurement of the plasma propagation speed. In the initial set of tests, primary arcs and the consequent current waveforms were measured in a Low Earth Orbit-type plasma. In a second set of tests, two electron guns with diffusers were used to provide an approximately uniform Geosynchronous Earth Orbit-type environment, and primary arcs and current waveforms were obtained. The objective of this and other round-robin tests is to characterize primary arc waveforms in terms of speed and degree of discharge of arc plasmas produced by primary arcs, and their dependences on environment, capacitance per unit area, arc voltage, temperature, and so on. The final goal is to allow engineering estimates of arc current peaks and half-widths to allow confident design and construction of space solar arrays, and to allow mitigation techniques to be evaluated. This is the first in an extended series of tests to be performed at six different U.S. facilities, and with participation from ten different U.S. organizations. [ABSTRACT FROM PUBLISHER]

Spacecraft charging, as a field, is continually being recharged by new developments in understanding, new materials and technologies, and new approaches to both new and old problems. I will discuss some of the new frontiers in understanding spacecraft charging in this paper, as well as referencing relevant papers from the 11th Spacecraft Charging Technology Conference. Spacecraft charging is highly material-property dependent. For example, the secondary electron emission, photoemission, bulk electrical resistivity, and surface resistivity are important parameters that help determine the extent of spacecraft charging (both on the surface and inside the spacecraft) in any given environment. Our understanding of these material properties is one of the new frontiers in spacecraft charging. I will discuss how these fundamental material properties have been found to depend on the following: proper measurement techniques, temperature, radiation flux, electric field, surface treatment, surface contamination from plumes and outgassing, surface modification through arcing and vacuum exposure, and synergistic effects. Modeling of spacecraft charging is a second new frontier. New developments in modeling have both improved our understanding of spacecraft charging and enabled us to model situations that are dynamic and geometrically complex. New schemes for treating both space and time variations of fields, particle fluxes, and spectra have made our modeling more precise and accurate. Now, many more spacecraft are being launched into low Earth orbit and the radiation belts. Modeling charging effects more accurately in those orbits will become more important than ever. A third new frontier in spacecraft charging is novel mitigation techniques. Surface materials and simple passive devices that emit electrons as fast as they are collected seem to make real-time charge mitigation cheaply and reliably achievable for the first time. Novel solar cell configurations and coverglass materials promise to make arcing, both of the primary electrostatic discharge (ESD) type and sustained arcing between cells or strings, a thing of the past. Superconducting cables may obviate the high voltages that lead to arcing. New cooperation between spacecraft and solar array manufacturers and spacecraft charging experts may help to prevent the spacecraft charging mistakes of the past. Furthermore, the final frontier is dealing with new materials and higher power requirements. Lightweight spacecraft materials are, in some cases, prone to exacerbate charging or arcing and may allow transmission of electromagnetic interference into sensitive electronics. New solar cell active materials may increase the effects of arcing on solar cell and solar array performance, even for primary ESD events. Higher power requirements may require longer transmission cables, which may increase the need for higher voltages, making arcing more likely. If superconducting cables become a reality, magnetics may become very important for spacecraft control and stability. What will happen to a superconducting cable if it must carry the increased current in an arcing event of very short duration? [ABSTRACT FROM PUBLISHER]

The Floating Potential Probe (FPP) operated on the International Space Station (ISS) from December 2000 to April 2001. During that time, it took many measurements of the ISS floating potential and the low-Earth-orbit electron density and temperature. Those measurements were used as inputs to the Environment WorkBench (EWB) model of ISS potentials (originally developed by the Science Applications International Corporation for NASA, but now sometimes called the Boeing Plasma Interaction Model), which is used even today to predict charging levels for ISS. FPP is now completely defunct, having been re- moved and jettisoned from ISS. With the advent of the new floating potential measurement unit (FPMU) on ISS and the beginning of ISS operations with three large sets of solar array panels instead of just one, a review of FPP measurements can offer comparisons with the new FPMU data and perhaps improve the accuracy of future ISS charging predictions. In particular, FPP measurements during times of low electron temperature and high electron density (the times of worst ISS charging) will be brought forward for comparison with the newly obtained FPMU data. [ABSTRACT FROM AUTHOR]

Emission spectra of arc plasmas contain valuable information regarding arc sites, plasma parameters and composition, and temporal dynamics of plasma expansion. Emission spectra within the range of 200-800 nm were measured for trigger arcs on triple junctions and sustained arcs between solar array strings. Spectra were recorded from arcs on several different brands of conventionally designed solar array samples immersed in simulated low-Earth-orbit plasma. The arc sites and cathode materials were determined for plasmas generated by primary discharges and sustained arcs. Comparative analysis of temporal dynamics of arc current pulse waveforms with spectral line intensities allowed obtaining estimates for plasma expansion rates. Statistical processing of spectral line intensities resulted in calculations of arc plasma electron temperatures and surface densities of some atomic species. The presence of a flux of energetic electrons (above 100 eV) was confirmed by analysis of the structure of the excited atom and ion energy levels. [ABSTRACT FROM AUTHOR]

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]

This marks the seventh issue of the IEEE Transactions on Plasma Science dedicated to Spacecraft Charging Technology. The theme of this issue is based on the papers presented at the 15th Spacecraft Charging Technology Conference, Kobe, Japan, in 2018. The history of spacecraft charging goes back to the first Spacecraft Charging Technology Conference, sponsored by AFRL and NASA, that was held at the U.S. Air Force Academy, Colorado Springs, CO, USA, in 1978. The 15th Spacecraft Charging Technology Conference was hosted by the Japan Aerospace Exploration Agency (JAXA) and the Graduate School of System Informatics, Kobe University. It continues a tradition of international conferences on a ~2-year cycle. This conference, as well as each previous one in the series, was a great success. The topical discussions have greatly helped in making progress in the fields of spacecraft charging, spacecraft-plasma interactions, and related areas. At the end of the 15th Conference, the assembly agreed to request publication of the proceedings of the conference in the IEEE Transactions on Plasma Science and to encourage the submission of the papers presented at the conference to the Journal. [ABSTRACT FROM AUTHOR]

An introduction to the fourth installment of Special Issues of "IEEE Transactions on Plasma Science" about spacecraft charging technology is presented.

The article offers information related to spacecraft charging technology discussed at the 11th Spacecraft Charging Technology Conference held in Albuquerque, New Mexico in September 2010. It highlights the advent of new solar cycle, new technologies for spacecraft systems and new satellites for space environment. It was organized by the U.S. Spacecraft Air Force Research Laboratory and David Cooke , Dale Ferguson and Shu T. lai were the main organizers.