Development of Field Emitter Array Technology for ED Tether Propulsion

Field Emitter Arrays (FEAs) are being developed for electron emission in electrodynamic tether applications. Instead of a single hot (i.e. high powered) emitter or a gas dependant plasma contactor, FEA systems consist of many (up to millions per square centimeter) of small (micron-level) cathode/gate pairs on a semiconductor wafer that effect cold emission at a relatively low voltage. Each individual cathode emits only micro-amp level currents, but a functional array is capable of multiple amp levels. This potentially provides a low power, relatively inexpensive technique for the amp level current emissions required for electrodynamic tether propulsion systems. Critical issues in the development of FEA systems which are discussed here are survivability in ionospheric and spacecraft environments, emission efficiency (i.e. power required to overcome space charge limits in the ionosphere), and electrical integration requirements. Tests of FEA devices are being conducted at the University of Michigan to evaluate their performance and results to date from these tests will be presented here.