Developing field emitter array cathode systems for electrodynamic tether propulsion
Field Emitter Array Cathodes (FEAC) are a new technology being developed for several potential spacecraft electron emission and charge control applications. Instead of a single hot (i.e. high powered) emitter, or a gas dependant plasma contactor, FEAC systems consist of many (hundreds or thousands) of small (micron level) cathode/gate pairs printed on a semiconductor wafer that effect a cold field emission at relatively low voltages. Each individual cathode emits only micro-amp level currents, but a functional array is capable of amp/cm2 current densities. It is hoped that thus FEAC offers the possibility of a relatively low-power, simple to integrate, and inexpensive technique for the high level of current emissions that are required for a tether propulsion mission. (Tether propulsion is a achieved by flowing current through a conducting tether, using the ionosphere as a current return path, thus requiring electron emission.) This paper covers research in progress at the University of Michigan to develop FEAC systems for electrodynamic tethers (EDTs). Challenges for a FEAC system in the EDT environment relating to space charge limits and non-ideal vacuum effects will be presented. Possible solutions via electrical and geometric configurations of FEAC systems, and the PIC and vacuum chamber tests being used to develop those solutions are discussed.
