Denis Payan

SPIS Open-Source Code: Methods, Capabilities, Achievements, and Prospects

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.

Secondary Electron Emission on Space Materials: Evaluation of the Total Secondary Electron Yield From Surface Potential Measurements

Secondary electron emission (SEE) is one of the main parameters controlling spacecraft potential. It also plays an important role in the triggering of the multipactor phenomenon occurring in waveguides (electron avalanche in microwave electric fields). In this paper, we propose an original method adapted to low-energy SEE measurements on dielectrics and conductors (incident electron energy below 20 eV). It is based on Kelvin probe (KP) surface potential measurements after electron irradiation. It is particularly well suited to insulating materials but can also be used on metals by letting the sample potential float. We present results of SEE measurements performed on metals used in waveguides, Kapton, Teflon, and CMX cover glass. In order to avoid any experimental artifact due to the earth magnetic field and conduct accurate low-energy measurements with the KP method, the distance between the electron gun and the sample is chosen to be negligible compared to the Larmor radius.

Pulsed electro-acoustic technique applied to in-situ measurement of charge distribution in electron-irradiated polymers

Dielectric materials are frequently used in satellite structures for substantial savings in weight. Their dielectric nature and the effect of different forms of radiation encountered in space combine to accumulate electrical charges resulting in the occurrence of electrostatic discharges which cause harmful interference with the electronic parts of the satellite, leading to its malfunction or to a total loss of equipment control. Therefore, the behavior of dielectrics under irradiation must be investigated before being used in space. A pulsed electroacoustic (PEA) device was mounted in an irradiation chamber to monitor the spatial distribution of electrons implanted into polymer films during electronic irradiation. Internal charge accumulation was clearly identified. Penetration depth versus energy was double checked by comparing PEA with surface potential data.

Parametric Study of a Physical Flashover Simulator

A physical flashover (FO) simulator has been developed by ONERA/DESP and CNES. The objective of this simulator is to represent the missing cells when testing small coupons in the laboratory. The aim of this paper is to present the results of a parametric study which has been performed on a sample constituted by a solar-array coupon made of six cells and a simulator constituted of a large surface of metallized polymeric film. Experiments were performed in the ONERA/DESP facility called JONAS which is a 9-m3 vacuum chamber equipped with a plasma source and a 10-keV electron gun. Electrostatic discharges (ESDs) occur in the inverted potential gradient (IPG) configuration obtained either by electrons or by plasma. The FO was characterized by measuring the neutralization current on the different surfaces with current probes. Therefore, we could get charge quantity, duration, and velocity. The surface potential of the coupon and the polymeric film were monitored before and after ESD by a potential probe, giving a good correlation with the amount of charges participating to the discharge. In order to determine what the limits of the FO are and what parameters can monitor it, we have studied different configurations: 1) electron or plasma IPG charging; 2) surfaces from 0.5 to 14 m2; 3) geometries-cylinder, ring, rectangular, and discontinuous surface; 4) primary arc locations-cell edge or interconnectors; and 5) absolute satellite capacitance values-between 300 pF and 300 nF. Analysis of the results is given for these configurations.

Measurements of the Flashover Expansion on a Real-Solar Panel—Preliminary Results of EMAGS3 Project

When a primary discharge occurs on a solar array, it is important to understand what would be the maximum flashover expansion. This value would then be representative of in-flight scenarios on full panel size. This paper presents the results of the experimental campaign performed in the frame of the European Space Agency EMAGS3 project “Flash-over evaluation on large solar panels” and where we measure flashovers in different conditions on a real-solar panel. This experimental campaign is conducted in the large vacuum chamber of Industrieanlagen-Betriebsgesellschaft mbH (IABG) (Germany) on a solar panel of 4 × 2 m provided by Astrium-Germany and organized in 52 linear strings of silicon cells covered by Cerium doped borosilicate glass (CMX) coverglasses (CG). During the test, several parameters are studied such as inverted potential gradient (IPG) obtained in plasma or in electrons and test of flashover expansion over a gap between panels by addition of a small panel. The main difficulty is in the evaluation of the value and homogeneity of the initial potential gradient to be able to determine the initial stored charge. The development of a model of flashover expansion has contributed significantly to the comprehension of the results and the assessment of the initial stored charge. During the first step (IPG by electrons at room temperature) ~ 200 electrostatic discharges (ESDs) are recorded of which 12 discharge of the theoretical stored charge in the CG. In IPG by plasma at room temperature, ~ 100 ESDs are recorded, 12 discharging of the theoretical stored charge including two that discharged the panel completely. With this test campaign we demonstrate that, even if the probability is not very high, an ESD on a solar panel could lead a flashover to expand and neutralize the complete surface of an 8- m2 panel. In addition, we see that the flashover can continue across a gap of 10 cm.

Space-Charge Detection and Behavior Analysis in Electron Irradiated Polymers

Charges accumulate on the spacecraft surface through various processes such as conduction, irradiation, ionization, and polarization. These charges can affect the space system operations via an electric current flowing in the structure or a locally generated electric field. This paper is focused on the analysis of electron behavior in polymeric films such as polymethylmetaacrylate and Teflon subjected to an electron irradiation. The charge distribution is detected during and after the irradiation in situ by pulsed electroacoustic method. Surface-potential and surface-current measurements are also performed to get further information on the charge displacement with time

Radiation Induced Conductivity in Teflon FEP Irradiated With Multienergetic Electron Beam

Teflon Fluorinated Ethylene Propylene (FEP), used as thermal blankets on satellites, has a specific electrical behavior under space ionizing environment. Charging behaviors of this dielectric material, under electron beam irradiation, is of special interest for future spacecraft needs. Hence, ground experimental parameters have been adjusted in order to distinguish between the different physical mechanisms that steers FEP charging potential. The effect of incident electron spectrum, electric field, and dose rate has been investigated through surface potential measurements during and after the irradiation process. The experimental results especially reveal that charging potential evolution as a function of time is not strongly dependent upon the electron spectrum and the electric field but varies noticeably with dose rate. These results have been analyzed in the light of a physical model that takes into account ionization, trapping/detrapping, and recombination mechanisms for negative and positive charges.

Polyimide and FEP charging behavior under multienergetic electron-beam irradiation

Surface and internal charging of dielectric materials is a potential cause of surface discharges and satellite anomalies, due to the fluctuating irradiation levels induced by space environment. Understanding conduction mechanisms and reducing charging levels are therefore important industrial issues for satellite designers and manufacturers. Surface potential measurements under irradiation and after charging (potential decay) are the most significant laboratory tests to qualify and understand the charging and discharging behavior of insulating materials. We present here experimental results obtained using the SIRENE facility at ONERA. Kapton and Teflon FEP films respond differently when subjected to a 20 keV charging electron beam combined with a 400keV ionizing electron beam. The physics underlying these experimental results is discussed. A simple numerical model has been developed. It is shown that different combinations of mobility, trapping and recombination may explain the results on both materials. The complex behavior observed on Teflon FEP may be attributed to the progressive deep trapping of the negative charge, enhancing holes recombination.

Electrostatic Discharge and Secondary Arcing on Solar Array—Flashover Effect on Arc Occurrence

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.

Study of signal treatment for a pulsed electro-acoustic measurement cell: a way of improving the transfer matrix condition number

This work is focused on the improvement of the condition number of the transfer function matrix in a pulsed electro-acoustic (PEA) cell. A numerical electro-acoustic model is developed with the software COMSOL. This model is one-dimensional and the system of equations with partial differential functions is solved using a finite element method in non-stationary situations. Using this model, we can establish the output voltage of the piezoelectric sensor and acoustic pressure at each point of the calculation domain. Our approach consists in recovering the charge distribution within the sample using a deconvolution method between the simulated output voltage and the transfer function of the PEA cell. Results show why some changes of the PEA cell such as the nature of materials or sensor geometry involve an ill-posed problem or ill-conditioned problem, and why other arrangements lead to a well-conditioned problem, more amenable to giving the appropriate solution.