Effect of Laser Produced Pinholes upon the Charging Characteristics of Spacecraft Thermal Control Surfaces

Differential charging of dielectric surfaces on spacecraft has received much attention in recent years because of the possible damage to spacecraft systems resulting from electrical breakdowns. Teflon presents a long term hazard because it can retain its charge for long periods after initial charging. In an attempt to reduce the charging of Teflon, a CO2 laser has been used to drill 100 ¿m diameter pinholes in metal backed Teflon. A radiation induced conduction layer from the front surface through the pinhole to the metal backing may provide a path for increased leakage currents and hence lower equilibrium surface potentials. Measurements of drilled Teflon samples irradiated with a monoenergetic electron beam indicate that an increased conduction to the metallized back of the samples and a reduction of secondary electron emission from the sample surface are accompanied by a reduction in equilibrium surface potential. The most interesting and perhaps most important effect noted is that drilled Teflon emits electrons after irradiation ceases. This emission combined with charge leakage to the metallized backing leads to a rapid reduction in surface potential. Drilled Teflon will therefore not maintain a charge for as long as will undrilled Teflon.