Field Emission Cathode for Electrodynamic Tethers

Electrodynamic (ED) tethers offer the potential of propellant-less propulsion with infinite specific impulse (Isp). To achieve it, an efficient electron source that contacts the space plasma without using propellant must be coupled with the ED tether. At present, the electrons are supplied by a hollow cathode (HC) plasma contactor with complex propellant management and storage and power-processing unit that typically dominate the ED tether system mass. Busek therefore proposes the development of a field emission electron source that uses no propellant, and is less massive and less complex than the HC system.In Phase I we will design, build, and test a field emission array cathode (FEAC) using Busek-grown carbon nanotubes as the emitters. The FEAC will consist of four paralleled emitter cells that will be tested individually and as a combined FEAC panel. The cell technology was already demonstrated as a neutralizer on a laboratory colloid thruster. Scaling up this technology while maintaining adequate current density is the major Phase I challenge.In Phase II, a complete FEAC panel system consisting of many cells will be developed per typical ED tether requirements. The system will include the FEAC power-processing unit and emission control circuitry for autonomous tether current matching.