MPD Thruster Performance Analytic Models

Abstract

Abstract. Magnetoplasmadynamic (MPD) thrusters are capable of accelerating quasi-neutral plasmas to high exhaust velocities using Megawatts (MW) of electric power. These characteristics make such devices worthy of consideration for demanding, far-term missions such as the human exploration of Mars or beyond. Assessment of MPD thrusters at the system and mission level is often difficult due to their status as ongoing experimental research topics rather than developed thrusters. However, in order to assess MPD thrusters' utility in later missions, some adequate characterization of performance, or more exactly, projected performance, and system level definition are required for use in analyses. The most recent physical models of self-field MPD thrusters have been examined, assessed, and reconfigured for use by systems and mission analysts. The physical models allow for rational projections of thruster performance based on physical parameters that can be measured in the laboratory. The models and their implications for the design of future MPD thrusters are presented.

High Power MPD Thruster Performance Measurements

“…32 For the baseline thruster operating with argon propellant, the critical ionization velocity is 8,720 m/s. The anode to cathode radius is 6.0 using the larger anode radius of 5.7 cm, and 3.4 using the anode lip radius of 3.2 cm.…”

“…Prior analyses of MPD thruster experiments have typically attributed this discrepancy to the larger fractional contribution of ohmically heated gas at lower currents; however, recent analysis by Choueiri indicates that the departure may instead result from pressure distributions created by the pinching components of the volumetric electromagnetic body forces. 30,31 As discussed by Choueiri and more recently by Gilland,32 Eqn, 8 is expected to hold for higher discharge currents where the electromagnetic thrust is the dominant contributor; however, the formula must modified for currents below the critical ionization current (ξ<1): Given a critical ionization velocity for argon of 8720 m/s and a thrust coefficient of 1.8x10 -7 N/A 2 , the critical ionization currents for the various mass flow rates used in the experiments are 3480 A, 4920 A, and 6025 A for mass flow rates of 0.25-g/s, 0.5-g/s, and 0.75-g/s, respectively. Using these values in Eqn.…”

“…As expected from prior MPD thruster experiments and theoretical analysis, the thruster operating voltage is generally higher at a given discharge current for lower mass flow rates, and deviates from a linear Ohm's-law relation at higher discharge currents. 26,32,33 The terminal voltage can be modeled as:…”

Modified Electromechanical Modeling and Parameters Analysis of Magnetoplasmadynamic Thruster

“…Therefore, a phenomenological or semi-empirical model is still required to predict the performance of MPDTs, and reveal the effect of several parameters (e.g., discharge current and applied magnetic field strength) on the thrust performance. To date, several theoretical models have been established for both self-field MPDTs (SF-MPDTs) [2,8,9] and applied-field MPDTs (AF-MPDTs) [5,6,[10][11][12][13][14][15]].…”

Electric Propulsion Concepts Enabled by High Power Systems for Space Exploration

“…19 Example self-field projected and measured performances are shown in Figure 5. The projected increase in efficiency is assumed to come from optimized thruster geometry and mass flow distribution, but has not yet been experimentally proven 21 .…”