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Full three-dimensional numerical models based on partical-in-cell with Monte Carlo collisions (PIC-MCC) simulations are developed to study ion thruster plasma interactions. 3-D simulation results for the NSTAR ion thruster plasma environment are presented.
Two particular cases of nonlinear wave interaction in a plasma column were investigated. The frequencies of the waves were on the order of magnitude of the electron plasma frequency, and ion motion was neglected. The nonlinear coupling of slow waves on a plasma column was studied by means of cold plasma theory, and the case of a plasma column surrounded by an infinite dielectric in the absence of a magnetic field was also examined. Nonlinear scattering from a plasma column in an electromagnetic field having it's magnetic field parallel to the axis of the column was investigated. Some experimental results on mode conversion in the presence of loss are presented along with some observations of nonlinear scattering, The effect of the earth's magnetic field and of discharge symmetry on the radiation pattern are discussed.
This paper presents an analysis of interactions between the Space Shuttle Orbiter and the ionosphere based on thermal plasma data obtained from a Spherical Retarding Potential Analyzer (SRPA) and a Langmuir Probe (LP) flown on the third Space Shuttle flight (STS-3) in March 1982. While previous work on spacecraft-plasma interactions has dealt with wake effects, the present work deals with effects that are seen in ram conditions that have not been previously discussed. One observation is a higher degree of plasma turbulence than has been reported from unmanned spacecraft measurements that manifests itself as a frequency component at 2.2 kHz in the SRPA signal. Also seen are unusually high number densities of what appear to be ions with a mass of at least 30 or 32 amu and a temperature in the range 2000-3000 K. Coincident with the enhanced molecular ion species, the temperature of the thermal electrons is seen elevated to above 5000 K. It is hypothesized that these measurements are evidence for a plasma instability resulting from the motion of the outgassing Orbiter through the ionosphere.
Description of laboratory studies of certain aspects of the spacecraft/space plasma interaction regarding, in particular, the near and intermediate wake regions. The plasma wind tunnel facilities and the diagnostic techniques employed in these tests are described. Results are obtained which concern the variation of the normalized ion flux with normalized distance along the wake axis downstream from a conducting spherical body, the variation of the normalized width of the disturbed region with normalized distance downstream from the body center, and the location of the point of maximum ion current enhancement as a function of body potential.
The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground-based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub-spacecraft System III longitude and the time, modulo 10 hours, of the first and subsequent magnetopause crossings.
The theoretical interpretation of observed interplanetary resonance luminescence patterns is used as one of the must promising methods to determine the state of the local interstellar medium (LISM). However, these methods lead to discrepant results that would be hard to understand in the framework of any physical LISM scenario. Assuming that the observational data are reliable, two possibilities which could help to resolve these discrepancies are discussed: (1) the current modeling of resonance luminescence patterns is unsatisfactory and has to be improved, and (2) the extrapolated interstellar parameters are not indicative of the unperturbed LISM state, but rather designate an intermediate state attained in the outer regions of the solar system. It is shown that a quantitative treatment of the neutral gas-plasma interaction effects in the interface between the heliospheric and the interstellar plasmas is of major importance for the correct understanding of the whole complex.
A wake model was defined for the NASCAP/LEO finite element model for the plasma interaction experiment (PIX-II) launched to study the interaction between high-voltage large solar arrays with the space plasma environment. The cell surface model considers the individual cells, distances between interconnects, and the fraction of surface covered by interconnects. Account is taken of the electrostatic potential around the spacecraft, which travels at 7500 mps, over five times the speed of thermal ions. Ram ions are produced ahead of the array and the wake ion density is described with a geometric shadowing model. The model correctly predicted the currents in high and low bias voltages when compared to orbital data. The panel snapover, however, was projected to occur at 100 V and instead occurred at 300 V, which indicates that the snapover state is bistable. Finally, a low potential was both predicted and measured in the wake.
As part of the SAMPIE (The Solar Array Module Plasma Interaction Experiment) program, the Langmuir probe (LP) was employed to measure plasma characteristics during the flight STS-62. The whole set of data could be divided into two parts: (1) low frequency sweeps to determine voltage-current characteristics and to find electron temperature and number density; (2) high frequency turbulence (HFT dwells) data caused by electromagnetic noise around the shuttle. The broadband noise was observed at frequencies 250-20,000 Hz. Measurements were performed in ram conditions; thus, it seems reasonable to believe that the influence of spacecraft operations on plasma parameters was minimized. The average spectrum of fluctuations is in agreement with theoretical predictions. According to purposes of SAMPIE, the samples of solar cells were placed in the cargo bay of the shuttle, and high negative bias voltages were applied to them to initiate arcing between these cells and surrounding plasma. The arcing onset was registered by special counters, and data were obtained that included the amplitudes of current, duration of each arc, and the number of arcs per one experiment. The LP data were analyzed for two different situations: with arcing and without arcing. Electrostatic noise spectra for both situations and theoretical explanation of the observed features are presented in this report.
As a part of the SAMPIE (The Solar Array Module Plasma Interaction Experiment) program, the Langmuir probe (LP) was employed to measure plasma characteristics during the flight of STS-62. The whole set of data could be divided into two parts: (1) low frequency sweeps to determine voltage-current characteristics and to find the electron temperature and number density; (2) high frequency turbulence (HFT) data caused by electromagnetic noise around the Shuttle. Broadband noise was observed at 250-20,000 Hz frequencies. Measurements were performed in ram conditions; thus, it seems reasonable to believe that the influence of spacecraft operations on plasma parameters was minimized. It is shown that ion acoustic waves were observed, and two kinds of instabilities are suggested for explanation of the origin of these waves. According to the purposes of SAMPIE, samples of solar cells were placed in the cargo bay of the Shuttle, and high negative bias voltages were applied to them to initiate arcing between these cells and the surrounding plasma. The arcing onset was registered by special counters, and data were obtained that included the amplitudes of current, duration of each arc, and the number of arcs per one experiment. The LP data were analyzed for two different situations: with arcing and without arcing. Electrostatic noise spectra for both situations and a theoretical explanation of the observed features are presented in this paper.
Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. The average time constant for sample charging was estimated between 25 and 50 seconds for all samples. It appears that current drops off by approximately a factor of 3 over the charging time of the sample. All samples charged in the forward and reverse bias directions, demonstrated hysteresis. Current jumps were only observed in the forward or positive swept voltage direction. There is large dispersion in tile critical snapover potential when repeating sweeps on any one sample. The current ratio for the first snapover region jumps between 2 and 4.6 times, with a standard deviation less than 1.6. Two of the samples showed even larger current ratios. It is believed the second large snapover region is due to sample outgassing. Under certain preset conditions, namely at the higher neutral gas background pressures, a perceptible blue-green glow was observed around the conductor. The glow is believed to be a result of secondary electrons undergoing collisions with an expelled tenuous cloud of gas, that is outgassed from the sample. Spectroscopic measurements of the glow discharge were made in an attempt to identify specific lines contributing to the observed glow.
The Voyager 1 measurements made during the Titan flyby reveal that Saturn's rotating magnetospheric plasma interacts directly with Titan's neutral atmosphere and ionosphere. This results from the lack of an intrinsic magnetic field at Titan. The interaction induces a magnetosphere which deflects the flowing plasma around Titan and forms a plasma wake downstream. Within the tail of the induced magnetosphere, ions of ionospheric origin flow away from Titan. Just outside Titan's magnetosphere, a substantial ion-exosphere forms from an extensive hydrogen-nitrogen exosphere. The exospheric ions are picked up and carried downstream into the wake by the plasma flowing around Titan. Mass loading produced by the addition of exospheric ions slows the wake plasma down considerably in the vicinity of the magnetopause.
The Earth's ionosphere is an important element in solar-terrestrial energy transfer processes. As a major terrestrial sink for many solar and magnetospheric events, the ionosphere has characteristic features that are traced to such seemingly remote phenomena as solar flares, radiation belt wave-particle interactions and magnetospheric substorms. In considering the multiple of solar-terrestrial plasma interactions, it is important to recognize that the high-latitude ionosphere is not altogether a simple receptor of various energy deposition processes. The high-altitude ionosphere plays an active feedback role by controlling the conductivity at the base of far-reaching magnetic field lines and by providing a plasma source for the magnetosphere. Indeed, the role of the ionosphere during magnetospheric substorms is emerging as a topic for meaningful study in the overall picture of magnetospheric-ionospheric coupling.
A large number of experimental and analytical efforts have been directed toward understanding the plasma sheath growth and discharge phenomena which lead to high-voltage solar array/space plasma interactions. An important question which has not been addressed is how the voltage gradient in the plasma sheath near the surface of such an array may affect these interactions. The purpose of the experimental study described in this paper is to examine the merging of the sheaths around biased slits in a dielectric and how this affects the collection of electrons through these slits. The data, which are obtained by emissive probes and direct measurement of the current collected through the slits, indicate that when the sheaths merge the current collection by the slits is significantly altered with the most positive slit collecting more electrons than it otherwise would. Therefore, the effect of a voltage gradient in the sheath around a solar array should be considered when evaluating solar array performance.
A wide range of opportunities is provided by the electrodynamic tether to more fully understand the generation of waves in plasmas, the behavior of field aligned currents, the behavior of large body-space plasma interactions, and for process simulation, using the electrodynamic tether to study processes and phenomena relevant to solar system and astrophysics plasma physics. The electrodynamic tether offers a means of study and experimentation in space which will provide a rich yield in new scientific results and will enhance the understanding of space plasma physics. It also has promising technological applications (e.g., the generation of electrical power and thrust) which may be highly significant to future space operations.
During an Extravehicular Activity (EVA), if the Extravehicular Mobility Unit (EMU) makes galvanic contact with the International Space Station (ISS), a negative Floating Potential (FP) can lead to an arcing hazard when it exceeds -45.5 V, and a positive FP can produce a DC current high enough to stimulate the astronaut’s muscles (5 mA), and also cause a hazard. The Boeing Space Environments team developed and utilizes a Plasma Interaction Model (PIM) in order to calculate the ISS FP based on the plasma environment, ISS velocity, geomagnetic field, solar array and ISS orientation, and solar array regulation to support EVA planning operations. Presently, the model excludes the sheath capacitance, resulting in the total potential drop being across the dielectric surface of the vehicle. Data from the Floating Potential Measurement Unit (FPMU) show this assumption to be generally true. However, Rapid Charging Events (RCE) are often observed in the FPMU data at eclipse exit when the electron number density, Ne, is low (less than 5(sub e)10 m (exp-3)). During these events, the FP can rise more than 40 V in one to five seconds. There is then a relaxation phase where the FP drops back to the normal FP values. The PIM model is not capable of producing these RCEs. It was thought that the inclusion of the sheath in PIM could improve the charging predictions, particularly as related to RCEs. A parametric study was performed to determine what portion of the measured FP is across the sheath for a range of Ne experienced by the ISS, and if the inclusion of the sheath in PIM is necessary. Results show that the potential drop across the sheath is negligible at times when the N(sub e) is greater than 1(sub e)11 m-3. However, there appears to be a transitional region between 1(sub e)10 m(exp -3) and 1(sub e)11 m(exp -3) where the sheath capacitance becomes more significant. During those conditions the potential drop across the sheath can be larger than the potential drop across the dielectric for short periods (1-5 seconds). These results agree remarkably well with measurements made by the FPMU. The inclusion of the sheath explains why high charging measurements occur when the Ne is low at eclipse exit and even times when the solar arrays are not a significant driver (i.e., potentials often rise as the ISS flies through spread-F). Results also show that the RCEs are not a safety concern because the potential drop across the dielectric surface does not exceed -45.5 V. In that case, the EMU would not arc. This gives high confidence in the low probability of an arcing hazard occurring.
NASA’s Gateway will provide the capability for sustaining a human presence in cis-lunar space. Operations of the Gateway will include spacecraft dockings, extra vehicular activities (EVA), and high-power solar arrays. NASA’s experience with the International Space Station highlighted the importance of evaluating spacecraft charging effects for such operations. For crewed spacecraft, which tend to employ the use of dielectric surfaces in this dynamic plasma environment, reliance on spacecraft charging simulation packages, such as the NASA/Air Force Spacecraft Charging Analyzer Program (Nascap-2k) [Mandell et al., 2006] and Spacecraft Plasma Interaction System (SPIS) [Roussel et al., 2008], is required to understand the risks to hardware and humans. The variability in the lunar plasma environment as the Moon revolves around the Earth, lunar wake effects, and a strong dependency on photoemission and secondary electron emission creates challenges for spacecraft charging analysis. The Design Specification for Natural Environments (DSNE) [NASA, MSFC] is the primary resource for space environments affecting NASA’s crewed missions, and the DSNE provides plasma environments in a standard form for input into simulation packages. NASA developed the existing lunar plasma environment using data from Geotail [Nishida, 1994] along with published lunar plasma wake models [Halekas et al., 2005] based on Lunar Prospector. Since 2011, NASA’s twin Acceleration Reconnection Turbulence & Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) satellites [Angelopoulos, 2010] have been collecting high resolution plasma and fields observations within the lunar plasma environment providing a much larger dataset of the plasma properties in cislunar space. This research compares the existing lunar plasma environment definition with ARTEMIS data and makes recommendations on the refinement of the environment definition for future lunar missions.
Electrostatic approximation of resonant four-wave interaction of electron plasma oscillations
Beam-plasma interaction to amplify millimeter waves