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A new Spacecraft Plasma Interaction Software has been developed in the frame of the Spacecraft Plasma Interaction Network (SPINE). This software is designed to simulate the kinetic processes of ions and electrons, taking into account their space charge and their interaction with spacecraft surfaces. It is freely available worldwide in open source. While the development and the qualification of the software functionalities were under the responsibility of a consortium led by ONERA under contract with the European Space Agency, the test and validation of the applicability of the code for solving problems in plasma physics remained under SPINE responsibility. The validation program includes step-by-step applications of the software to sheath modeling in simple geometry, artificial plasma injection, and spacecraft charging. We report here on the progress along this program, including Langmuir probe tests with spherical and cylindrical geometry and comparison with other numerical methods. Index Terms--Langmuir probe, numerical techniques, particle-in-cell (PIC) plasma modeling, spacecraft charging.

Cumulative electrostatic discharges (ESDs) on spacecraft solar cells result in the degradation of their performances. In this paper, silicon solar cells are tested in inverted voltage gradient situation obtained in plasma. ESDs occurring on the cells are detected by both electrical and optical signatures. To be representative of flight ESDs, the test setup must avoid unwanted coupling with ground arcs. The degradation is then evaluated by measuring the current--voltage characteristic of the cell in darkness. The equivalent shunt resistance allows quantifying this degradation, which can be attributed to material deposition on the cell edge or to local cell carbonization due to arcing. Visual inspection of the cells allows us to correlate ESD location and local degradation of the cell. The important parameter for solar cell degradation is the amount of energy dissipated during the discharge. A model of the plasma expansion from the cathode spot is compared to measurement. This model explains the current rise during the first phase of the discharge, which is the same for normal ESDs and coupling with ground ESDs. Index Terms--Arcing, electrostatic discharges (ESDs), plasma expansion model, solar cell degradation.

A good representativeness of the test setup used for the qualification of solar arrays is fundamental. We know now that the flashover current involved in the electrostatic discharge is related with the total dielectric surface neutralized during the electrostatic discharge. This paper presents experiments on samples of different sizes, performed in a large vacuum chamber, JONAS, installed in ONERA/DESP, Toulouse, France. The samples are tested in the inverted voltage gradient configuration obtained with electrons. We observed that secondary arcs obtained on a large sample (i.e., with a long flashover) had much longer durations than those on a small sample, i.e., the flashover is a critical parameter for secondary arc initiation and sustainment. Index Terms--Electrostatic discharge (ESD), plasma generation, solar power satellites.

Several aspects of plume effects of field-effect electric propulsion (FEEP) were studied. We first estimated the contamination by cesium deposit due to charge exchange of fast ions and slow neutrals and to direct neutral impingement. Levels are rather low, with local maximums of a few tens or hundreds of angstroms per year, and not much more than 1-10 [Angstrom] farther from thruster nozzles. Neutralization of the ions emitted by FEEPs was also addressed, both concerning FEEP ion space-charge compensation and spacecraft net current, i.e., the floating potential issue. With the presence of a cathode-grounded neutralizer, the spacecraft was shown to float somewhat negative with little dependence on the ambient environment. Index Terms--Cesium, field-effect electric propulsion (FEEP), floating potential, space vehicle propulsion, surface contamination.

ONERA plasma tank JONAS is populated of drifting Ar+ argon ions representative of Low Earth Orbit environment, produced by a Kaufman source, and slow ions created by charge exchange with the background pressure of argon. When testing a mock-up or space equipment in this tank, it is often important to determine the drifting and slow ion densities in various locations. The orbital and radial motion models are compared to experimental current--voltage measurements and to numerical results. In the range of parameters used in this paper, the radial motion model is more adapted than the orbital-motion-limited model to determine slow ion density. Nevertheless, the number of measurements is necessarily limited and discriminating between fast and slow ions is not easy. A complementary approach consists in performing a numerical simulation of the plasma dynamics in the tank. Provided the modeled physics is validated, and the modeling is calibrated through measurements, this approach supplies fast and slow ion densities everywhere with an acceptable factor of uncertainty. This approach has been followed by characterizing in detail a given plasma configuration in JONAS and modeling it with Spacecraft Plasma Interaction Software open source code. The mock-up was a simple plate. We measured the plasma characteristics through numerous current--voltage sweeps and current space profiles at given probe potential. The modeling was based on fast ion beam measurements close to the source and the residual pressure. Index Terms--Charge EXchange (CEX), plasma diagnostics, plasma simulation, wake effect.

In this paper, recent improvements in the modeling capabilities of the Spacecraft Plasma Interaction Software (SPIS) code are presented. New developments still in progress are also reported. They should in particular allow modeling of fast dynamical phenomena, including processes as challenging as the second part of ESDs, i.e., the vacuum arc and its related flashover plasma expansion. The first, electronic, part of ESDs is already modeled. The range of SPIS application domains and studies is reviewed. An interesting study case, the assessment of charging at multiple-scale levels, is presented here in more detail. Charging in geostationary-Earth-orbit conditions is simulated from the spacecraft scale down to a solar-cell-gap (hence, decameters to millimeter) scale. This self-consistent computation shows that macroscopic inverted-voltage-gradient (IVG) cases may differ at microscopic scales close to a solar-cell gap, due to the local blocking of secondary emission by the small-scale electric-field configuration. We consider this effect as the likely origin of the different ESD triggering thresholds, depending whether IVG is obtained by electrons or plasma. Index Terms--Electrostatic discharges, modeling, plasmas, spacecraft.