Charging Behavior of the H-II Transfer Vehicle by Active Electron Emission

A field-emission cathode (FEC) is a simple electron source that emits electrons just by applying a strong electric field on a solid surface. The Japan Aerospace Exploration Agency has been developing FECs, especially for the application in electrodynamic tether (EDT) propulsion for active space-debris removal systems. An in-orbit experiment on EDT technologies including the FEC was conducted in early 2017 on the H-II transfer vehicle 6 (HTV-6). In the experiment, the FEC operated successfully throughout the 1-week mission and the maximum electron emission current of about 5.8 mA was obtained. An electric potential monitor measured the HTV potential with reference to the ambient plasma and the measurement results revealed that active electron emission mitigated the negative potential of the HTV in sunlight by up to 15 V. Reasonable estimation results of the incoming and outgoing of charged particles on the HTV body were also obtained by simple quantitative analysis.