The total electrode fall voltage in a channel of magnetoplasmadynamic (MPD) thruster was determined by using "zero-limit approximating method", which is one of the classical methods widely used in the arc welding field. A new five-channel parallel-plate MPDT was designed and operated in a quasi-steady mode. This paper presents the measurement of the discharge voltage vs. the electrode gap for gaps from 1 mm to 4 mm. The extrapolated zero-gap intercept resulted in 18 V, which was considered as the total electrode-fall voltage. The electrode-fall voltage did not depend on the discharge current unless the discharge current exceeded onset threshold. It is considered that most of the electrode fall is deposited on the cathode side since the space potential at the inter-electrode region was almost equal to the anode potential.
2009 The Japan Society for Aeronautical and Space Sciences