An Impacting Descent Probe for Europa and the other Galilean Moons of Jupiter

We present a study of an impacting descent probe that increases the science return of spacecraft orbiting or passing an atmosphere-less planetary body of the solar system, such as the Galilean moons of Jupiter. The descent probe is a carry-on small spacecraft (< 100 kg), to be deployed by the mother spacecraft, that brings itself onto a collisional trajectory with the targeted planetary body in a simple manner. A possible science payload includes instruments for surface imaging, characterisation of the neutral exosphere, and magnetic field and plasma measurement near the target body down to very low-altitudes (~1 km), during the probe's fast (~km/s) descent to the surface until impact. The science goals and the concept of operation are discussed with particular reference to Europa, including options for flying through water plumes and after-impact retrieval of very-low altitude science data. All in all, it is demonstrated how the descent probe has the potential to provide a high science return to a mission at a low extra level of complexity, engineering effort, and risk. This study builds upon earlier studies for a Callisto Descent Probe (CDP) for the former Europa-Jupiter System Mission (EJSM) of ESA and NASA, and extends them with a detailed assessment of a descent probe designed to be an additional science payload for the NASA Europa Mission.Comment: 34 pages, 11 figure

Evaluation of the communications impact of a low power arcjet thruster

The interaction of a 1 kW arcjet thruster plume with a communications signal is evaluated. A two-parameter, source flow equation has been used to represent the far flow field distribution of the arcjet plume in a realistic spacecraft configuration. Modelling the plume as a plasma slab, the interaction of the plume with a 4 GHz communications signal is then evaluated in terms of signal attenuation and phase shift between transmitting and receiving antennas. Except for propagation paths which pass very near the arcjet source, the impacts to transmission appear to be negligible. The dominant signal loss mechanism is refraction of the beam rather than absorption losses due to collisions. However, significant reflection of the signal at the sharp vacuum-plasma boundary may also occur for propagation paths which pass near the source

Cold ions of ionospheric origin observed at the dayside magnetopause and their effects on magnetic reconnection

Thesis (Ph.D.) University of Alaska Fairbanks, 2015Magnetic reconnection at the dayside magnetopause is one of the most important mechanisms that efficiently transfers solar wind particles, momentum, and energy into the magnetosphere. Magnetic reconnection at the magnetopause is usually asymmetric since the plasma and magnetic field properties are quite different in the magnetosphere and the magnetosheath. Cold dense plasma, originating either directly from the ionosphere or from the plasmasphere, has often been observed at the adjacent magnetopause. These cold plasmas may affect reconnection since they modify the plasma properties on the magnetospheric side significantly. This dissertation presents case and statistical studies of the characteristics of the cold ions observed at the dayside magnetopause by using Cluster spacecraft datasets. The plasmaspheric plumes have been distinguished from the ionospheric outows using ion pitch angle distributions. The ionospheric outows feature unidirectional or bidirectional field-aligned pitch angle distributions, whereas the plasmaspheric plumes are characterized by 90° pitch angle distributions. The occurrence rates of the plasmaspheric plumes and ionospheric outows and their dependence on the solar wind/Interplanetary Magnetic Field (IMF) conditions have been investigated. It is found that the occurrence rate of plasmaspheric plume or ionospheric plasma strongly depends on the solar wind/IMF conditions. In particular, plasmaspheric plumes tend to occur during southward IMF while ionospheric outows tends to occur during northward IMF. The occurrence rate of the plasmaspheric plumes is significantly higher on the duskside than that on the dawnside, indicating that the plasmaspheric plumes may lead to a dawn-dusk asymmetry of dayside reconnection. Furthermore, this dissertation investigates the behavior of the cold dense plasma of ionospheric origin during magnetic reconnection at the dayside magnetopause. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection near the subsolar magnetopause, the colder ions are simply entrained by E x B drift at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play a very limited role in magnetic reconnection process. Finally, this dissertation examines a controlling factor that leads to the asymmetric reconnection geometry at the magnetopause. It is demonstrated that the separatrix and ow boundary angles are greater on the magnetosheath side than on the magnetospheric side of the magnetopause, probably due to the stronger density asymmetry rather than magnetic field asymmetry at this boundary

Self consistent kinetic simulations of SPT and HEMP thrusters including the near-field plume region

The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.Comment: 14 pages, 11 figures This work was presented at 21st International Conference on Numerical Simulation of Plasmas (ICNSP'09

Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations

Abstract Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution, and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date. Key PointsQuantitative analysis of the first balloon REP with closely conjugate EMIC wavesOur simulation suggests EMIC waves to be a viable cause for the REP eventThe adopted model is proved to be applicable to simulating the REP event

Detailed modeling and analysis of spacecraft plume/ionosphere interactions in low Earth orbit

Detailed direct simulation Monte Carlo/particle‐in‐cell simulations involving the interaction of spacecraft thruster plumes with the rarefied ambient ionosphere are presented for steady thruster firings in low Earth orbit (LEO). A nominal mass flow rate is used to prescribe the rocket exit conditions of a neutral propellant species for use in the simulations. The charge exchange interactions of the steady plume with the rarefied ionosphere are modeled using a direct simulation Monte Carlo/particle‐in‐cell methodology, allowing for a detailed assessment of nonequilibrium collisional and plasma‐related phenomena relevant for these conditions. Results are presented for both ram‐ and wake‐flow configurations, in which the thrusters are firing into (ram) or in the direction of (wake) the free stream ionosphere flow in LEO. The influence of the Earth's magnetic field on the development of the ion plume is also examined for three different field strengths: two limiting cases in which B →0 and B → ∞ , and the LEO case in which B =0.5 Gs. The magnetic field is found to have a substantial impact on the resulting neutral and ion plumes, and the gyroscopic motion of the magnetized ions results in a broadening of the ion energy distribution functions. The magnetic field model also incorporates a cross‐field diffusion mechanism which is shown to increase the current density sampled far from the thruster. Key Points Particle‐based model for plume/ionosphere interactions Charge‐exchange reactions modeled using detailed DCS/TCS data B ‐field has a strong influence on the development of plumesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106930/1/jgra50833.pd

Characterization of a 50kW Inductively Coupled Plasma Torch for Testing of Ablative Thermal Protection Materials Using Non-Air Gases

Thermal protection systems have been a major area of study since the advent of space flight, but recent efforts towards crewed spaceflight missions have placed a new importance on the development of such systems. The 50 kW Inductively Coupled Plasma (ICP) Torch Facility at The University of Texas at Austin allows for rapid testing of high-temperature aerospace materials essential to the development of thermal protection systems in planetary re-entry applications. This ICP Torch Facility has been previously characterized using air as the test gas. However, planets of interest for future exploration have atmospheric compositions that differ from air, so testing heat shield materials in the presence of other gases is critical. To address this disparity between tested and actual environment, the current work characterizes the torch using various combinations of argon, CO2, and N2 by determining its operational range at various power settings, mass flow rates, and mixtures these gases. At each setting, the cold-wall heat flux is also measured to determine the range the torch is able to provide. Measurements indicate that using pure Ar gives the torch the largest operating range with regard to power setting and gas injection mass flow rate, and mixing argon into other gases drastically increases the stable operating range compared to the pure gas. Pure CO2 does not form a stable plasma discharge, but a mixture of 50% argon and 50% CO2 (by mass) provides stable operation up to 40 slpm total gas flow rate with a maximum heat flux of 98 W/cm2. Smaller percentages of CO2 allow the cold-wall heat flux to be increased to 110 W/cm2. Pure N2 forms a stable plasma discharge, but the operating range is very limited, providing stable operation up to 20 slpm total gas flow rate with a maximum heat flux of 110 W/cm2.Aerospace Engineering and Engineering Mechanic

Spacecraft plume interactions with the magnetosphere plasma environment in geostationary Earth orbit

Particle‐based kinetic simulations of steady and unsteady hydrazine chemical rocket plumes are presented in a study of plume interactions with the ambient magnetosphere in geostationary Earth orbit. The hydrazine chemical rocket plume expands into a near‐vacuum plasma environment, requiring the use of a combined direct simulation Monte Carlo/particle‐in‐cell methodology for the rarefied plasma conditions. Detailed total and differential cross sections are employed to characterize the charge exchange reactions between the neutral hydrazine plume mixture and the ambient hydrogen ions, and ion production is also modeled for photoionization processes. These ionization processes lead to an increase in local plasma density surrounding the spacecraft owing to a partial ionization of the relatively high‐density hydrazine plume. Results from the steady plume simulations indicate that the formation of the hydrazine ion plume are driven by several competing mechanisms, including (1) local depletion and (2) replenishing of ambient H+ ions by charge exchange and thermal motion of 1 keV H+ from the ambient reservoir, respectively, and (3) photoionization processes. The self‐consistent electrostatic field forces and the geostationary magnetic field have only a small influence on the dynamics of the ion plume. The unsteady plume simulations show a variation in neutral and ion plume dissipation times consistent with the variation in relative diffusion rates of the chemical species, with full H2 dissipation (below the ambient number density levels) approximately 33 s after a 2 s thruster burn.Key PointsSpacecraft hydrazine plume interacts with GEO via charge exchange and photoionization processesMagnetized hydrazine ion plumes envelop spacecraft, and neutral plumes convect downstreamIon and neutral plume dissipation times longer and species‐dependentPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135463/1/jgra52433_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135463/2/jgra52433.pd

Spacecraft-plasma-debris interaction in an ion beam shepherd mission

This paper presents a study of the interaction between a spacecraft, a plasma thruster plume and a free floating object, in the context of an active space debris removal mission based on the ion beam shepherd concept. The analysis is performed with the EP2PLUS hybrid code and includes the evaluation of the transferred force and torque to the target debris, its surface sputtering due to the impinging hypersonic ions, and the equivalent electric circuit of the spacecraft-plasma-debris interaction. The electric potential difference that builds up between the spacecraft and the debris, the ion backscattering and the backsputtering contamination of the shepherd satellite are evaluated for a nominal scenario. A sensitivity analysis is carried out to evaluate quantitatively the effects of electron thermodynamics, ambient plasma, heavy species collisions, and debris position