Internal Charging Research Articles

Realistic Worst Case for a Severe Space Weather Event Driven by a Fast Solar Wind Stream.

Satellite charging is one of the most important risks for satellites on orbit. Satellite charging can lead to an electrostatic discharge resulting in component damage, phantom commands, and loss of service and in exceptional cases total satellite loss. Here we construct a realistic worst case for a fast solar wind stream event lasting 5 days or more and use a physical model to calculate the maximum electron flux greater than 2 MeV for geostationary orbit. We find that the flux tends toward a value of 106 cm−2·s−1·sr−1 after 5 days and remains high for another 5 days. The resulting flux is comparable to a 1 in 150‐year event found from an independent statistical analysis of electron data. Approximately 2.5 mm of Al shielding would be required to reduce the internal charging current to below the National Aeronautics and Space Administration‐recommended guidelines, much more than is currently used. Thus, we would expect many satellites to report electrostatic discharge anomalies during such an event with a strong likelihood of service outage and total satellite loss. We conclude that satellites at geostationary orbit are more likely to be at risk from fast solar wind stream event than a Carrington‐type storm.

Electron Environment Characteristics and Internal Charging Evaluation for MEO Satellite

By analyzing the newly released in situ data in medium earth orbit (MEO) of global positioning system satellites, we studied the spatiotemporal distribution and statistical characteristics of electrons over one solar cycle. The Weibull distribution of daily-averaged flux cumulative occurrence probability is proven. For >2-MeV electron flux, the determination coefficient of Weibull fitting is 99.92%. In the magnetic storm of late July 2004, the radial diffusion of electrons to low L-shell position was obvious. The center of 0.04-MeV electrons moved inward from L = 6 to L = 4.3 in the main phase and moved outward slowly in the recovery phase. In 0-4 MeV range, the in situ electron flux data are consistent with the AE9 mean and MEO-v2 model. The percentile of the AE9 model is also validated. The differential spectra are fitted based on exponential function at different percentiles. We also develop a rapid analysis method of internal charging in a changing electron environment. Using this method, we find that the electric field of internal charging fluctuates a lot because of the time-varying electron environment in MEO. The charging processes of different dielectrics (time constant ranges from 1 day to 100 days) in one solar cycle are also simulated. The longer the time constant, the bigger is the maximum charging electric field. But the worst case flux needed for discharging hazard evaluation is smaller. The daily-averaged worst case flux for charging assessment is not applicable.

Electron Transportation Simulation for Spacecraft Internal Charging Based on Reverse Monte Carlo Method

To make an estimation of the internal charging effect caused by the high energy electrons, a high-efficient 3-D transportation simulation code for satellite has been developed based on a reverse Monte Carlo (RMC) method implemented in Geant4. Charge production distribution, dose distribution in the sensitive volume has been simulated via forward Monte Carlo (FMC) and RMC, respectively, for the same geometry construction. Simulation results show that the computing time is significantly reduced in this RMC electron transportation simulation, especially when the sensitive volume is much smaller than the entire geometry. As an example, the computing time of RMC for a sensitive volume accounting for 0.0001% in the entire structure is only 1/500 of that of FMC. Difference of the results between RMC simulation and traditional Monte Carlo simulation is less than 10%.

Cellular polypropylene foam films as DC voltage insulation and as piezoelectrets — A comparison

Polymer foams are in industrial use for several decades. More recently, non-polar polymer foams were found to be piezoelectric (so-called piezoelectrets) after internal electrical charging of the cavities. So far, few studies have been carried out on the electrical-insulation properties of polymer foams. Here, we compare the piezoelectric and the DC-voltage electrical-insulation properties of cellular polypropylene (PP) foams. Their cavity microstructure can be adjusted via inflation in high-pressure nitrogen gas in combination with a subsequent thermal treatment. While inflation is effective for improving the piezoelectricity, it is detrimental for the electrical-insulation properties. The original cellular PP foam shows a breakdown strength of approximately 230 MV/m, within the same range as that of solid PP. The breakdown strength decreases with increasing degree of inflation, and the dependence on the foam thickness follows an inverse power law with an exponent of 1.2. Nevertheless, up to a thickness of 140 μm (3.5 times the original thickness), the breakdown strength of cellular-foam PP films is at least 7 times that of an air gap with the same thickness. In addition, the influence of high temperatures and high humidities on the piezoelectricity and the breakdown strength of cellular PP was studied. It was found that the piezoelectric d33 coefficient decays rapidly already at 70 °C, while the breakdown strength slightly increases during storage at 70 or 90 °C. Under a relative humidity of 95%, the breakdown strength increases with storage time, while the piezoelectric d33 coefficient slightly decreases.

Internal Charging Characteristics in Typical Navigation Satellite Orbits

Internal charging is an important hazard for navigation satellites, which operate in outer electron radiation belt and experience a very variable radiation environment because of the inclination of orbits. A rapid analysis method of internal charging is introduced, including physical model, conductivity model, shielding and electron transportation algorithm, and charging calculation method. Using this method, we calculate the charging processes of dielectric in medium earth orbit (MEO), geostationary earth orbit (GEO), and inclined geosynchronous orbit (IGSO). The results show that charging field fluctuates a lot in orbit and variation rate of field is proportional to electron flux. The saturated charging field in MEO is higher than that in GEO, and the field in GEO is higher than that in IGSO. So, the internal electrostatic discharging risk in MEO, GEO, and IGSO decreases in turn. If conductivity of dielectric is smaller, saturated field is larger and the difference of field in MEO, GEO, and IGSO is smaller. The dark and radiation-induced conductivity (RIC) of dielectric are important parameters in simulation, so we study the impact of conductivity in charging processes. In IGSO and MEO, when dark conductivity-induced time constant of charging is greater than orbital period and RIC is not large, the deposited electrons between different orbits accumulate and the charging field increase constantly. In this situation, the dark conductivity has a big influence on internal charging and it is important to measure it accurately.

Electrostatic behaviour of space used materials in regard of internal charging met on spacecrafts

This paper is dedicated to the characterisation of charging behaviour of space used polymers in space electron environment. Spacecrafts are indeed submitted in Medium Earth Orbit (MEO) to severe fluxes of electrons with energies ranging from a few keV to several MeV. For qualification of materials used on satellites and the prediction of their electrostatic behaviour in space environment, it is therefore important to tests these materials in representative environment. These experiments have been carried out at ONERA, The French Aerospace Lab (Toulouse, France) in the SIRENE facility. Different polymers (PEEK, ETFE, Kapton®, polyurethane and silicone varnish, polyurethane based paint) have been characterised to extract the main electric parameter that steer their charging behaviour in space environment: the radiation induced conductivity (RIC). These materials have then been tested in representative environment so as to study the evolution of their conductivity and charging behaviour as a function of the received radiation dose (for low and high dose levels). From these experiments, it was possible to extract the physical parameters that steer RIC and assess numerically their charging levels in specific MEO environment.

A new charging model for exposed dielectric of spacecraft

In order to consider comprehensively the effects of high-energy electron radiation and space plasma on the exposed dielectrics outside a spacecraft, in this paper, a model named surface and internal coupling charging model for the exposed dielectric of spacecraft is proposed, and its numerical solution is obtained. It is based on the deep dielectric charging model, with considering the interaction between the exposed dielectric surface and the ambient plasma by adding an incident charging current into the boundary in the proposed model, and the potential of infinite plasma is regarded as the referential potential (zero potential). The determinate solution of the model is analyzed and a numerical solution in one-dimensional case is provided by using an iterative algorithm to overcome the coupling between electric field and conductivity. The solution includes the potential of spacecraft body, the distribution of dielectric potential, and the electric field. Moreover, the new model is compared with surface charging model and internal charging model. The results show that the new model has an advatage of depicting the electric field exactly with respect to the surface charging model; if the internal deposition current is equal to zero, the new model degenerates into the one depicting the surface charging. It considers the effect of surface potential on charging results compared with the internal charging model. The three kinds of currents, namely the surface incident current, the internal deposition current and the leakage current, are considered comprehensively in the new model. Among them, the leakage current is the most complicated, which is determined by the potential and the dielectric conductivity affected by the electric field, radiation dose rate, and temperature. Using this new model, the surface and internal coupling charging simulation of the exposed dielectric can be performed. Therefore, the new model can provide a more comprehensive assessment for the charging of exposed dielectric of spacecraft.

Incorporating Radiation Effects Into AE9/AP9

This paper describes a framework for incorporating linear radiation effects into the statistical machinery of the AE9/AP9 radiation climatology model software via “kernel” files. Users can provide their own kernels without modification of the software. Kernels can be applied to a variety of radiation effects such as proton single-event effect rate, internal charging current, ionizing dose, and nonionizing dose. Kernels can be generated for custom shielding geometry and materials and for custom parts or material susceptibilities.

Validation Through Experiments of a 3-D Time-Dependent Model of Internal Charging

A new model of dielectric conductivities has been implemented in SPIS-IC. It allows modeling the time-dependent behavior of the charge transport and the electric potential inside payload components under realistic radiation environments in space. The simulation results have been compared to experiments on four validation cases going from simple 1-D geometry to more complex 3-D components such as a d-type connector. The comparison shows a good agreement in most of the cases, and the discrepancies are explained in certain cases. Finally, the results have been analyzed in term of discharge probability and severity. This study also shows the great importance of time-dependent modeling of the radiation-induced conductivity.

3-D NUMIT: A General 3-D Internal Charging Code

A general 3-D internal charge analysis method, 3-D NUMIT, was developed by combining a Monte Carlo radiation transport simulation tool such as MCNPX or GEANT4 and a commercial finite-element analysis software such as COMSOL. The method was validated in 1-D cases with the analytical solution and NUMIT 2.0 and in a 3-D case with previously developed CB_IESD. The internal charging behavior of a semi-rigid coax cable in space was successfully analyzed using this 3-D NUMIT method.

Experimental Measurement of Low-Intensity and Long-Duration Internal Charging Behavior

We report initial results from the EU FP7 Spacestorm project on the experimental behavior of commonly-used space dielectric materials in an electron environment where the incident electron current is significantly below safe levels specified by design standards. The realistic electron environment facility (REEF), which uses an intense strontium-90 beta-emitting radioactive source to simulate the space environment, has been recommissioned at the University of Surrey for this purpose. Using a combination of shielding and variable source-sample separation REEF can achieve a very wide dynamic range in electron current, from the very high levels associated with an extreme space weather event, down to the levels below the European Cooperation for Space Standardization low temperature (<25 °C) safety threshold of 0.02 pA/cm2. In order to allow for the accumulation of significant levels of charge at such a low current, these experiments need to be run continuously for several weeks, far in excess of typical experimental investigations of internal charging phenomena. Here we report our early results from these experiments on samples of polyether ether ketone thermoplastic polymer material. Irradiating using a range of electron currents provides insight into the effect not just of inherent material properties but also of secondary effects such as radiation-induced conductivity.

Modeling of Electric Fields Inside Spacecraft Dielectrics Using In-Orbit Charging Current Data

Internal charging caused by energetic electrons is a threat to critical space infrastructure such as Europe's Galileo navigation satellites, however, the mechanism involved and its relationship to space weather is still poorly understood. While the electric field developed inside on-board dielectrics is accepted to be of prime importance, it has never been measured in orbit. On the other hand, internal charging currents have now been measured in a GPS-like medium Earth orbit (MEO) over a ten-year period, so we have used these data to model the electric fields of concern. The measured charging currents provide both charge deposition and dose rate inputs to the electric field model, the latter allowing the introduction of radiation-induced conductivity (RIC) to improve realism. As expected we find that RIC is a mitigating factor for the electric fields but they can still become very large, e.g., a 1.0-mm thickness of PEEK under 0.5 mm of Al shielding would be at risk of breakdown almost throughout the mission. We find that RIC tends to reduce sensitivity to space weather perturbations of the environment such as the April 2010 storm event, and hence longer term average fluxes seem to be more important. This seems physically reasonable for the examples studied but we also know that some satellite anomalies do show a correlation with space weather storms and short term (daily) electron fluences and so further work is needed to understand such cases: for example model parameters could be adjusted to see under what circumstances short term variations are more influential. To enable the progressive improvement of such modeling in future we recommend wider deployment of charging current sensors, especially in MEO and geostationary orbits.

Internal Charge Estimates for Satellites in Low Earth Orbit and Space Environment Attribution

Space assets are continuously bathed by charged particles making their components susceptible to the effects of spacecraft charging. While their orbits are not embedded within the radiation belts, low earth orbiting assets with high inclinations do pass through the horns of these belts during each polar crossing, transiting through potentially dangerous charged particle populations many times per day. Occasionally, these low altitude horns include significant populations of energetic ~1 MeV electrons, which can penetrate typical spacecraft shielding and accumulate within dielectric materials and on ungrounded conductors, a process known as internal charging. The National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites (POES) have experienced on-orbit anomalies in the boost voltage regulator (BVR) that is suspected to be associated with the accumulation and discharge of ~800 keV electrons. We have used observations from the Medium Energy Proton and Electron Detector (MEPED) instrument and a first principles model of charge accumulation [11] to develop estimates of electron internal charge (IC) accumulation over the lifetime of each POES and Metop spacecraft for a range of typical discharge time constants. With the advantage afforded by a larger database of anomalies, we are able to show that these BVR anomalies are generally not attributable in a simple way to the accumulation and subsequent discharge from >800 keV nor a higher fluence of lower energy >300 keV electrons. To the best of our knowledge, this paper presents the first long-term estimates of IC for spacecraft in highly inclined low earth orbits.

Extreme relativistic electron fluxes in the Earth's outer radiation belt: Analysis of INTEGRAL IREM data

AbstractRelativistic electrons (E &gt; 500 keV) cause internal charging and are an important space weather hazard. To assess the vulnerability of the satellite fleet to these so‐called “killer” electrons, it is essential to estimate reasonable worst cases, and, in particular, to estimate the flux levels that may be reached once in 10 and once in 100 years. In this study we perform an extreme value analysis of the relativistic electron fluxes in the Earth's outer radiation belt as a function of energy and L∗. We use data from the Radiation Environment Monitor (IREM) on board the International Gamma Ray Astrophysical Laboratory (INTEGRAL) spacecraft from 17 October 2002 to 31 December 2016. The 1 in 10 year flux at L∗=4.5, representative of equatorial medium Earth orbit, decreases with increasing energy ranging from 1.36 × 107 cm−2 s−1 sr−1 MeV−1 at E = 0.69 MeV to 5.34 × 105 cm−2 s−1 sr−1 MeV−1 at E = 2.05 MeV. The 1 in 100 year flux at L∗=4.5 is generally a factor of 1.1 to 1.2 larger than the corresponding 1 in 10 year flux. The 1 in 10 year flux at L∗=6.0, representative of geosynchronous orbit, decreases with increasing energy ranging from 4.35 × 106 cm−2 s−1 sr−1 MeV−1 at E = 0.69 MeV to 1.16 × 105 cm−2 s−1 sr−1 MeV−1 at E = 2.05 MeV. The 1 in 100 year flux at L∗=6.0 is generally a factor of 1.1 to 1.4 larger than the corresponding 1 in 10 year flux. The ratio of the 1 in 10 year flux at L∗=4.5 to that at L∗=6.0 increases with increasing energy ranging from 3.1 at E = 0.69 MeV to 4.6 at E = 2.05 MeV.

Preparation of semi-insulating PANI/PMMA coating and its applications in internal charging protection

The internal charging effect is one of the most important factors threatening satellite’s life in the space environment. In this paper, a semi-insulating conformal coating is prepared on the circuit board surface by spray method aimed to eliminate the charging. The coating is composed of two layers. A polymethyl methacrylate (PMMA) base layer followed by top layer made of PMMA matrix polyaniline (PANI) composite with a surface resistivity of 1.49 × 1011 Ω. The structure and morphology of PANI were investigated by FTIR, XRD, and TEM. Anti-internal charge testing of PANI/PMMA conformal coating is performed by the internal charging simulation device. The results showed that the coating can prevent the discharge phenomenon effectively.

Recent Progress on Piezoelectric and Triboelectric Energy Harvesters in Biomedical Systems.

Implantable medical devices (IMDs) have become indispensable medical tools for improving the quality of life and prolonging the patient's lifespan. The minimization and extension of lifetime are main challenges for the development of IMDs. Current innovative research on this topic is focused on internal charging using the energy generated by the physiological environment or natural body activity. To harvest biomechanical energy efficiently, piezoelectric and triboelectric energy harvesters with sophisticated structural and material design have been developed. Energy from body movement, muscle contraction/relaxation, cardiac/lung motions, and blood circulation is captured and used for powering medical devices. Other recent progress in this field includes using PENGs and TENGs for our cognition of the biological processes by biological pressure/strain sensing, or direct intervention of them for some special self‐powered treatments. Future opportunities lie in the fabrication of intelligent, flexible, stretchable, and/or fully biodegradable self‐powered medical systems for monitoring biological signals and treatment of various diseases in vitro and in vivo.

Transient Analysis of Spacecraft Exposed Dielectric Charging Using SICCE

Spacecraft exposed dielectric interacts directly with the ambient plasma and may be faced with energetic electron irradiation. Using the charging model surface and internal coupling charging model for spacecraft exposed dielectric (SICCE), it is possible to investigate this special charging process, including both surface charging (SC) and deep dielectric charging. Based on the finite-difference time-domain method, a transient solution of the SICCE in the 1-D case is proposed in this paper with adequate verifications. An important improvement is made to the SICCE by employing secondary electron yield formula in Katz form, which is the same with Spacecraft Plasma Interaction Software (SPIS) and NASA Charging Analyzer Program (NASCAP) $-2k$ . The typical charging environment for exposed dielectric is assumed Geosynchronous Earth Orbit (GEO) worst plasma environment combined with Flumic3 energetic electron irradiation. The charging characteristics of a 3-mm polyimide board with front surface exposed to this typical environment and back surface connected to the spacecraft body is investigated. The total charging process in time-domain can be divided into three stages: the first is dominated by fast SC of spacecraft body with the typical time less than 1 s determined by spacecraft capacitance, the following stage lasts until the dielectric surface potential reaches equilibrium with the charging time of several hundred seconds determined by dielectric board capacitance, and the deep dielectric charging dominates in the third part with the charging time more than 2 h. If the magnitude of the body potential is larger than the dielectric surface potential in equilibrium, overcharge and feedback appear in the surface potential evolution. Peak electric field appears on the point connecting spacecraft body and reaches a maximum value in charging equilibrium. In the case of multiple roots of SC equation, transient solution has the advantage of avoiding unstable charging potential. This investigation can further enrich engineers’ understanding of spacecraft exposed dielectric charging.

Additive effects under the series of EOS in space application VLSI circuits

One of the problems of space technology is the spacecraft on orbit charging effect. Series of EOS (electrical overstress) are caused by internal charging affect VLSI (very large-scale integrated) circuits, which may lead to its damage. The results of the EOS series with energy below the threshold of failure for modern submicron VLSI circuits design are presented. The obtained results confirm the possibility of accumulation of the effects of damage from exposure of EOS series in modern VLSI circuits and allow you to get the dependence describing the additive nature of damage the VLSI circuits during exposure to subthreshold EOS. The obtained dependence agrees well with the Arrhenius equation, which indicates the thermal nature of the damage under the series of subthreshold energy EOS. The method of the VLSI circuits testing is proposed to determine the level of the VLSI circuits EOS hardness to the effects of multiple different pulsing voltages.

Grain‐scale supercharging and breakdown on airless regoliths

AbstractInteractions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain‐grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature‐dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain‐to‐grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

Extreme internal charging currents in medium Earth orbit: Analysis of SURF plate currents on Giove-A

Relativistic electrons can penetrate spacecraft shielding and can damage satellite components. Spacecraft in medium Earth orbit pass through the heart of the outer radiation belt and may be exposed to large fluxes of relativistic electrons, particularly during extreme space weather events. In this study we perform an extreme value analysis of the daily average internal charging currents at three different shielding depths in medium Earth orbit as a function of L∗ and along the orbit path. We use data from the SURF instrument on board the European Space Agency's Giove-A spacecraft from December 2005 to January 2016. The top, middle, and bottom plates of this instrument respond to electrons with energies >500 keV, >700 keV, and >1.1 MeV, respectively. The 1 in 10 year daily average top plate current decreases with increasing L∗ ranging from 1.0 pA cm−2 at L∗=4.75 to 0.03 pA cm−2 at L∗=7.0. The 1 in 100 year daily average top plate current is a factor of 1.2 to 1.8 larger than the corresponding 1 in 10 year current. The 1 in 10 year daily average middle and bottom plate currents also decrease with increasing L∗ ranging from 0.4 pA cm−2 at L∗=4.75 to 0.01 pA cm−2 at L∗=7.0. The 1 in 100 year daily average middle and bottom plate currents are a factor of 1.2 to 2.7 larger than the corresponding 1 in 10 year currents. Averaged along the orbit path the 1 in 10 year daily average top, middle, and bottom plate currents are 0.22, 0.094, and 0.094 pA cm−2, respectively.