An unavoidable step in the process of space exploration is to use high-power, very large spacecraft launched into Earth orbit. Obviously, the spacecraft will need powerful energy sources.Previous experience has shown that electrical discharges occur on the surfaces of a high-voltage array, and these discharges (arcs) are undesirable in many respects. Moreover
A number of experiments have been done to study characteristics of the plasma contamination and electromagnetic radiation generated by arcing on anodized aluminum plates immersed in low-density plasma. The low-Earthorbit plasma environment was simulated in a plasma vacuum chamber, where the parameters could be controlled precisely. Diagnostic equipment included two antennas, a mass spectrometer, a spherical langmuir probe, a wire probe, and a very sensitive current probe to measure arc current. All data except for mass spectrometry were obtained in digitalform with a samplinginterval of 2.5 ns that allowed us to study the radiationspectrum at frequencies up to 200 MHz. We found that the level of interference considerably exceeds the limitations on the level of electromagnetic noise set by technical requirements on Space Shuttle operation. Experiments with two independently biased plates have shown that the arcing onset on one plate generates a pulse of current on the second plate and that the secondary current pulse has a signi cant amplitude. The sampling interval for mass spectrometry was 250 ms. This allowed us to obtain the rate of plasma contamination due to arcing. A signi cant degradation of the coating layer was determined by measurement of the resistance of the plate, which had experienced a few hundred arcs. NomenclatureA = atomic number a = diameter of hole in the shield, m C = capacitance, F D = langmuir probe diameter, m D h = diameter of damaged area, m d = thickness of coating layer, m E = electrical eld strength, V/m e = electron charge, C F = ux of atoms, atoms/m 2 s f = frequency, Hz f e = plasma frequency, Hz I m = amplitude of discharge current, A L = distance between plates, m l = antenna length, m M = atomic mass, kg N e = number of electrons N i = number of ions n e = electron number density, m ¡3 p = neutral gas pressure, torr Q = electrical charge, C R = resistance, Ä T e = electron temperature, eV t = time, s t d = time delay, s U = bias voltage, V U a = amplitude of antenna voltage, V V p = plasma expansion speed, m/s ± = skin depth, m ½ = coating material density, kg/m 3 ¿ = pulse duration, s
The electrical insulating materials used on solar cell array undergo degradation primarily due to their interaction with high energy protons, electrons and spaceplasma. The parameters that indicate the quality of the insulating materials are the surface resistivity and the dissipation factor of the insulating material.Pressure, temperature and radiation are synergistic multifactor stress parameters (1).The vacuum effects and the thermal effects have been investigated extensively but independently ( 2 ) . In order to understand the degradation processes and deterioration in the quality of the dielectric materials the theoretical model must be supported by experimental measurement of the materials. For accurate measurement of the change in above quantities an instrumentation and measurement systems was designed constructed and tested (3). Kapton, an insulating material used in space power system was investigated for its dielectric properties. This paper reports the preliminary results of the measurement of @ Proceedingssurface and volume resistivities, dielectric constant and dissipation factor of Kapton type H and V thin films of various thicknesses, at different temperatures and vacuum. MEASUREMENTS Two types of Kapton -H type and V type-were selected for investigation. The thicknesses chosen for H type were 1,2,3 and S mil and for V type they were 2,3 and 5 mil. manufacturers suggested specification. However, the samples showed variations in thickness. The sample thickness was measured These were at fourperipheral points and in the center The average of these values was used in calculating the experimental results. The surface resistivity and volume resistivity were measured under 20 millitorr pressure and 30, SO and 70 degree celcius temperatures. At each temperature the sample was subjected to 100 and 200 volts in sequence. The measurements of capacitance and dissipation factor were made on one set of samples at the temperature of 30, SO and 70 degrees celcius at 6 volts and 1000 Hz and another set at room temperature (25 "c) and 1989 Southeastcon 1377
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