Space electrodynamic tether propulsion technology: System considerations and future plans

Space electrodynamic tethers offer the opportunity for in-space “propellantless” propulsion around planets with a magnetic field and ionosphere. This propulsion is accomplished by converting the magnetic force on the tether current into propulsive or drag thrust to either increase or decrease the orbital energy of the spacecraft system. To validate electrodynamic-tether thrusting, we must be able to demonstrate sustainable currents and effective methods of collecting and emitting electron current under varying ionospheric conditions. To date, significant tether current flow (~1 A) to/from the tether’s end collectors in the Earth’s ionosphere has been demonstrated as part of NASA’s TSS-1R mission in 1996, though the maximum possible current was not tested. Here, we review system-level issues associated with effective electrodynamic-tether operation, which include ionospheric and motional-EMF variability as well as details of the tether “end”, contacts under varying ionospheric conditions. We also survey potential future near-Earth applications of electrodynamic tethers as currently conceived. Applications ranging from orbit transfer of payloads, orbit maintenance, and end-of-mission deorbiting will be described. The NASA ProSEDS mission, an important first step to understanding electrodynamic-tether capabilities, is discussed.