Random and Sine-Spectrum Vibration Testing of Pyrolytic Graphite Ion Optics

Abstract

*† ‡ § ** The long lifetime requirements of interplanetary exploration missions are driving the need to develop long-life components for the electric propulsion thrusters that are being considered for these missions. One of the primary life-limiting components of ion thrusters are the optics, which are continuously eroded during the operation of the thruster. Pyrolytic graphite is being considered for high power ion thruster optics because its erosion resistance is ten times greater than that of molybdenum and its density is among the highest of the carbon based materials. The risk of damage to the grids due to inter-grid impact during launch is, however, a source of concern because of the relatively low strength and brittle nature of the material. To address this concern, a set of flat, rectangular pyrolytic graphite grids was subjected to both random vibration and elevated sine spectrum vibration tests. Both spectra were chosen to be representative of a deep space mission, and were used as the excitation input transverse to the optics plane. Ultrasonic and visual inspection methods showed very little indication of damage due to either vibration environment. Test results, a complete description of the test, as well as the associated structural analyses and material investigations are presented herein.