The Charging Characteristics of Kevlar-Polyester Composite Materials under Electron Beam Irradiation

The response of antenna aperture materials to irradiation by an electron beam was studied to evaluate the potential impact of these materials on the electromagnetic environment of spacecraft in orbit. The materials investigated were Kevlar-polyester composite and the same material coated with PV-100 white paint. The study was directed toward determining the equilibrium charging conditions achieved by these materials under irradiation and the severity of the electrical discharges that occur. The samples were irradiated by an electron flood gun having a beam current density in the range of 0.5 to 2.5 nA/cm2. Equilibrium surface voltages were inferred from the energy spectra of secondary electrons obtained with a curved plate electrostatic energy analyzer. Substrate currents were measured to infer bulk conductivities and to determine the frequency, duration, and intensity of the electrical discharges occurring on the sample. The experimental configuration was designed to selectively simulate the effect of electrical and mechanical feed-throughs and the effect of support posts on the charging characteristics of the materials. The characteristics of the two materials were similar in many respects. The surface leakage currents are comparable in both cases and low amplitude bipolar discharges are observed to occur for beam voltages as low as 5 keV. The discharges occurred more frequently when the support post was grounded than in the floating configuration. There was a slightly greater tendency for the unpainted Kevlar to charge, with the equilibrium surface voltage 1.7 to 2.4 kV less negative than the beam voltage. The painted Kevlar charged 2.