Current collection to and plasma interaction with femtosatellite-and CubeSat-scale electrodynamic tether subsystems

The efficacy of an electrodynamic tether system in generating a propulsive force or harvesting energy is limited, in part, by its ability to collect current from and emit current to the surrounding ambient plasma. This process is facilitated by active and passive electron emitters. Laboratory experiments were designed and conducted in a ground-based vacuum chamber to investigate the current-voltage characteristics of potential devices within the plume of a plasma source capable of producing ion and electron temperatures and densities similar to that found in low Earth orbit. We achieved active electron emission using a tungsten filament and lanthanum hexaboride crystal (approximately milliamps and microamps, respectively). We achieved a passive plasma contact by biasing a planar surface coated in a thin layer (15 Ω/sq) of indium tin oxide, which yielded current levels comparable to that of alodined aluminum. We also developed laboratory experiments designed to validate certain assumptions made about the behavior of ultra-small electron collecting interfaces for femtosatellites using short electrodynamic tethers.