Current closure for the electrodynamic tether

Summary form only given, as follows. One of the outstanding issues in the operation of an electrodynamic tether in space is the collection and return of electrons by the payload. In the tethered-satellite-system experiment, the tethered satellite is expected to collect electrons, and the collected current is returned from the shuttle using an electron gun. Is a current closure involving the collected and returned electrons essential for the operation of the electrodynamic tether? Since the tether system moves with an orbital velocity of about 8 km/s, the current closure leading to the neutralization of the space charges created by the collection of electrons by the satellite and the ejection of the current from the shuttle occurs behind the system in the wake region. On the other hand, the electron collection occurs from the fresh plasma into which the satellite continually ploughs through. If the collected current is efficiently ejected using the electron gun from the shuttle, the problem of current collection is separated from that of current closure behind the system. The space charges left behind in the wake should be neutralized by appropriate current system set up in the infinitely large volume of the space plasma. Both these problems of current collection and charge neutralization are simulated using particle-in-cell (PIC) codes. Both 2.5-D and fully 3-D codes are employed to study the problems. Results from such simulations are presented.