VEHICLE CHARGING EFFECTS DURING ELECTRON-BEAM EMISSION FROM THE CHARGE-2 EXPERIMENT

The CHARGE-2 sounding rocket payload was designed to measure the transient and steady-state electrical charging of a space vehicle at low Earth orbit altitudes during the emission of a low-power electron beam from the vehicle. In addition to the electron gun, the payload contained several diagnostics to monitor plasma and waves resulting from the beam/space/vehicle interaction. The payload was configured as a mother-daughter arrangement with the two parts connected by an insulated conducting wire tether that extended to a maximum length of 426 m during the flight. In the paper we discuss the configuration of the payload, a description of the science instruments, and the flight operation plan. We then present some initial results from the flight, addressing the prime objective of the mission to study vehicle charging. The results show that the 1-keV electron beam was generated at beam currents of 1-48 mA emerging from the exit aperture of the electron gun. The beam emission always resulted in positive charging of the vehicle, which occurred as a two-step process; a transient charging took place about 10 iis after beam turn-on, followed by a slower rise to a steady-state potential in a period of the order of milliseconds. The maximum steady-state potential we measured was 560 V for a 17-mA beam emission current. The highest transient potential we measured was 290 V for a 31-mA beam current. Studies of the distribution of currents and voltages in the complete tethered system show that the return currents are supplied from the space charge limited sheath currents above 240 km. Below 240 km the return current to the mother appears to be enhanced by the effects of beam plasma interactions. Detectable effects of the electron beam in vehicle potential and photon emission from the beam are seen for beam currents as low as 1 mA. © 1989 American Institute of Aeronautics and Astronautics, Inc. All Rights Reserved.