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A carbon nanotube-based field-emission cathode (FEC) has been researched and developed by the Japan Aerospace Exploration Agency mainly for space-debris removal systems with electrodynamic tether (EDT) propulsion. An in-orbit experiment to demonstrate the EDT technologies including the FEC was planned and conducted in early 2017. The FEC operated well without any critical trouble during the one-week mission period. The data obtained include its electron emission capability to space plasma and its durability in low Earth orbit, which suggest the prospect of using the FEC in space.

In this study, the active removal of space debris is studied from the point of view of technological feasibility. First, the actual debris distribution is analyzed to determine which debris objects should be removed considering the effectiveness in preventing collisional cascading and feasibility such as the delta-V required for rendezvous with the objects. Target regions such as sun-synchronous orbit and a 1,000km altitude, 83 degree inclination orbit are then selected and rendezvous with debris object in these regions are studied. Electrodynamic tether is promising as a highly-efficient propulsion system required for debris de-orbit in these regions. A small piggyback-launched satellite to dispose of one debris object, and a dedicated debris removal satellite which removes several debris objects from crowded regions are proposed. Precise numerical simulations of EDT are performed to evaluate the de-orbit time.

In order to understand plasma properties of hollow cathodes, a numerical simulation code with Hybrid-PIC model has been developed, in which ions and electrons are modeled as particles and fluid, respectively. In this study, as a first step, the applicability of the model is demonstrated, and then the influences of the emitter temperature on the flow field are discussed for a discharge current of 30 A and a mass flow rate of 1 mg/s. The electron density for the maximum emitter temperature of 1900 K agrees well with the experimental data from JPL. The results also show that the electron density tends to be higher with lower emitter temperature due to the higher electron temperature inside the cathode tube. The higher electron temperature is caused by the energy loss suppression resulting from the higher sheath voltage on the emitter surface. It was also found that charge exchange collisions shift the location of the electron density peak upstream.