Overview of U.S. academic programs in electric propulsion

Abstract

We present an overview of recent electric propulsion research activities carried out by twelve research groups at US academic institutions. The groups are at: Colorado State University, Cornell University, Massachusetts Institute of Technology, Ohio State University, Pennsylvania State University, Princeton University, Stanford University, University of Illinois at Urbana-Champaign, University of Michigan, University of Southern California and Worcester Polytechnic Institute The research activities are sponsored by NASA, DoD, DoE and other governmental agencies and industrial partners and include experimental, analytical and numerical work related to: ion thrusters, plasma contactors, colloidal thrusters, Hall thrusters, ablative and gas-fed pulsed plasma thrusters, magnetoplasmadynamic thrusters, arcjets, microwave-heated thrusters, field emitter array cathodes, micropropulsion, thruster plumes and tethers. 1 Colorado State University Work at Colorado State University over the past year in areas related to electric propulsion has focused on understanding events that accompanied the tether failure during the TSS-1R electrodynamic tether mission and on increasing ion thruster grid lifetimes by reducing the sputter yields of grid materials. A new ∗Chief scientist at EPPDyL. Assistant Professor, Applied Physics Group, MAE Dept. and Associated Faculty at the Dept. of Astrophysical Sciences. Senior Member AIAA. †Presented at the 35th AIAA Joint Propulsion Conference, Los Angeles, CA, June 21-23, 1999. concept in plasma contacting has evolved from the former effort. Plasma Contacting with a Solid Expellant. The break on the tether during the second electrodynamic tether mission (TSS-1R) was followed by a highly unusual, yet efficient electron emission (plasma contacting) process from the broken end of the tether to the ambient space plasma. Experiments and analyses have been conducted which illustrate the important physical processes required for such a plasma contacting process to occur. Specifically, it has been shown that 1) a dense plasma discharge can be sustained by ionization of decomposed tether (primarily Teflon) vapors and 2) charge transport between the small strands of copper wire and a high density plasma that develops immediately adjacent to the wire occurs primarily via ions collected on the wire. The series of experiments and analyses that led to these conclusions and show that thermionic and/or field emission were not the mechanisms for direct electron emission from the wire are described in ref. [1]. Further analysis suggested a current conduction mechanism similar to that observed in liquid mercury cathodes where intense ionization occurs near the cathode and current continuity is achieved via ions collected on the cathode and to a lesser extent by secondary electrons emitted from it. Experiments were also conducted in which operation of hollow cathodes on vaporized Teflon at performance levels similar to those of cathodes operating on xenon was demonstrated. Normal operation was realized even when these cathodes were made of copper and when they were held near ambient temperatures. A