Experimental study of thrust performance of a Multimode Acceleration Coaxial (MAC) thruster

In-space Servicing, Assembly, and Manufacturing (ISAM) missions require propulsion systems capable of achieving both high specific impulse (I sp ) and high thrust under limited power constraints. To avoid the complexity of separate electrical and chemical propulsion systems, JAXA is exploring multimode propulsion technologies. This study introduces a novel Hall thruster-based concept, the Multimode Acceleration Coaxial (MAC) thruster, and experimentally evaluates its performance. While the MAC thruster’s structure resembles a Hall thruster with an internally mounted cathode, it is distinguished by a cathode designed to function as a high-flow gasjet using a long nozzle. Initial testing confirmed that this nozzled cathode maintains discharge characteristics equivalent to conventional orificed cathodes. The cathode was subsequently integrated into a BreadBoard Model (BBM) MAC thruster for evaluation. Performance in gasjet, Hall, and combined modes, supplemented by Faraday probe measurements, was evaluated in a vacuum chamber with an effective krypton pumping speed of 220,000 L/s. Background pressure was maintained below 7 mPa at a maximum total krypton injection rate of 58 mg/s. Results demonstrate that the “combined mode”, simultaneous Hall and gasjet operation, consistently exceeds the sum of the individual modes, achieving a thrust-to-power ratio exceeding 110 mN/kW using Krypton propellant.