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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

MPD thruster performance - Propellant distribution and species effects

Previous research has shown that MPD thruster performance, as measured by thrust, specific impulse, and efficiency, is limited by a so-called 'onset' current level. Experimental results are presented which show that the onset current level varies with the radial position of mass injection. Specifically, mass injection into either of two zones results in drastically different performance for both argon and xenon propellants. This difference in performance is evidenced by the onset current levels, the onset V-J signatures, and the overall V-J characteristics. The behavior of the thruster with the total mass flow split between the two zones follows a transition between the zonal behavioral limits. The behavior of propellant mixtures also follows a transition between the behavior of the individual propellant species. The flow region between the two zones is characterized by a particle number density discontinuity, a large axial current density, and a large electron Hall parameter, suggesting a possible correlation between observed onset phenomena and a shear-flow discontinuity located in the region between the two zones.

Kelly, A. J.↗
NASA NTRS1973

Performance of a modified downstream-cathode MPD thruster.

Discussion of the improvements incorporated since 1969 in a low-power MPD thruster design which is considered a potential candidate for satellite station keeping and attitude control. The improvements include a new cathode design, and changes in thruster geometry, with xenon used as the propellant. A better thermal design is found to be necessary for further improvement of the thruster.

Burkhart, J. A.↗
NASA NTRS1981

Thrust and efficiency of a self-field MPD thruster

Thrust and efficiency of a quasi-steady multi-MW argon MPD thruster are determined for one-millisecond current pulses. Terminal voltage and impulse bit per pulse are measured for a benchmark thruster geometry on a swinging gate thrust stand in a dielectric vacuum tank, at a background pressure of 0.0001 torr, for a range of argon flow rates and arc currents. The quasi-steady thrust data scale quadratically with arc current, and confirm previous estimates of the electromagnetic and electrothermal components of thrust from magnetic and pressure probe measurements. Thruster efficiency is found to increase monotonically with specific impulse, reaching a value of 25% for 4.5 to 6.0 g/sec at 2000 seconds. Results of further experiments show that the inferred specific impulse for voltage fluctuation onset can be increased to 3000 seconds, and the thrust efficiency to above 30%.

Burton, R. L.↗
NASA NTRS1990

Anode power deposition in quasi-steady MPD thrusters

Spatially resolved anode heat flux measurements of a pulsed quasi-steady MPD thruster have been made by embedding thermocouples to the inner surface of a hollowed anode. Results obtained using argon propellant at mass flow rates of 4 and 16 g/s with the thruster operating at currents between 8 and 24 kA are presented. The results show that the anode fall voltage increases linearly with thruster current and does not depend on propellant mass flow rate. The fraction of thruster power deposited into the anode is 42 percent at 1 MW and falls to less than 20 percent at 6 MW. At any given operating condition, there is an inverse relationship between the anode fall and anode current density.

Kelly, Arnold J.↗
NASA NTRS1991

Anode power deposition in an applied-field segmented anode MPD thruster

Anode heat flux measurements of a water cooled segmented anode applied-field MPD thruster were made to investigate anode heat transfer phenomena. Pure argon and argon-hydrogen mixtures were used as propellants for a variety of thruster currents, propellant mass flow rates, and axial applied magnetic field strengths. The thruster was operated in two modes; with all four segments active, and with two of the segments floating. In addition, thrust and specific impulse were determined for each operating condition. The results show that the heat flux to the anode increases monotonically with axial magnetic field strength and thruster current. Between 50 and 75 percent of the anode heat flux is transported by the current carrying electrons. Convective and radiative heat transfer account for the remaining portion of the power deposited in the anode. The addition of hydrogen to the argon propellant results in the reduction of the fraction of anode power deposited by the anode fall to a level equivalent to that deposited by convection and radiation.

Myers, R. M.↗
NASA NTRS1992

Numerical simulation of MPD thruster flows with anomalous transport

Anomalous transport effects in an Ar self-field coaxial MPD thruster are presently studied by means of a fully 2D two-fluid numerical code; its calculations are extended to a range of typical operating conditions. An effort is made to compare the spatial distribution of the steady state flow and field properties and thruster power-dissipation values for simulation runs with and without anomalous transport. A conductivity law based on the nonlinear saturation of lower hybrid current-driven instability is used for the calculations. Anomalous-transport simulation runs have indicated that the resistivity in specific areas of the discharge is significantly higher than that calculated in classical runs.

Caldo, Giuliano↗
NASA NTRS1984

MPD thruster operation with stepped current input

Experimental study of the response of a quasi-steady MPD thruster to an incremental increase or decrease in current illuminates the processes by which the discharge adjusts to changes in its operating level. For changes well below the onset condition, the thruster maintains quasi-steady operation throughout. Changes imposed near onset produce transition periods of non-quasi-steady operation. The duration of the transient appears to be determined by magnetic field diffusion in the portion of the discharge downstream of the thrust chamber.

Jahn, R. G.↗
NASA NTRS1991

Numerical simulation of self-field MPD thrusters

A fully two dimensional magnetohydrodynamics code was developed to predict self-field, steady-state MPD thruster performance. The governing equations are outlined, and methods of solution are presented. Model predictions are compared with experimental data for two thruster geometries over a range of discharge currents and mass flow rates. Model limitations are evaluated, and issues concerning quasi-steady versus steady-state thruster comparisons are discussed.

Lapointe, Michael R.↗
NASA NTRS1990

Diagnostics and performance of a 1/4-scale MPD thruster

The primary purpose of this study is to evaluate the performance and scaling characteristics of a 1/4-scale magnetoplasmadynamic (MPD) thruster operating with and without applied magnetic nozzle fields. The experiment was carried out with separate pulse forming networks for the thruster and the applied field solenoidal coil. A strong correlation of impact pressure signal with thruster current was noted. Also striking was the larger impact signal when the magnetic nozzle field was applied. Measurements of N(e) and T(e) from Langmuir probes have been made. Compatible interpretation of pressure with N(e), T(e), allow local velocity to be mapped, thus enhancing understanding of the acceleration process.

York, T. M.↗
NASA NTRS1991

Numerical simulation of self-field MPD thrusters

A fully two-dimensional magnetohydrodynamics code has been developed to predict self-field, steady-state MPD thruster performance. The governing equations are outlined, and methods of solution are presented. Model predictions are compared with experimental data for two thruster geometries over a range of discharge currents and mass flow rates. Model limitations are evaluated, and issues concerning quasi-steady versus steady-state thruster comparisons are discussed.

La Pointe, Michael R.↗
NASA NTRS1991

A preliminary characterization of applied-field MPD thruster plumes

Electric probes, quantitative imaging, and emission spectroscopy were used to study the plume characteristics of applied-field MPD thrusters. The measurements showed that the applied magnetic field plays the dominant role in establishing the plume structure, followed in importance by the cathode geometry and propellant. The anode radius had no measurable impact on the plume characteristics. For all cases studied the plume was highly ionized, though spectral lines of neutral species were always present. Centerline electron densities and temperatures ranged from 2 x 10 to the 18th to 8 x 10 to the 18th cu m and from 7500 to 20,000 K, respectively. The plume was strongly confined by the magnetic field, with radial density gradients increasing monotonically with applied field strength. Plasma potential measurements show a strong effect of the magnetic field on the electrical conductivity and indicate the presence of radial current conduction in the plume.

Myers, Roger M.↗
NASA NTRS1992

The MPD thruster program at JPL

The topics covered are presented in viewgraph form and include the following: engine lifetime assessment; lithium magnetoplasmadynamic (MPD) thruster development; and radiation-cooled, applied-field engine testing.

Goodfellow, Keith↗
NASA NTRS1991

LLNL contributions to MPD thrusters for SEI

Some of the topics covered with respect to the Lawrence Livermore National Laboratory's (LLNL's) contributions to Magnetoplasmadynamic (MPD) Thrusters for the Space Exploration Initiative (SEI) include: an IR camera, plasma-induced erosion/redeposition, the Mirror Fusion Test Facility-B (MFTF-B), the Thruster Lifetime Test Facility, the RACE Compact Torus Accelerator Facility, and a RACE program summary. Some of the other topics addressed include: flux contours for HAM simulation, comparison of RACE data of plasma ring formation with the HAM 2-D magnetohydrodynamic code, and the 2-D Ring Acceleration Code (TRAC).

Hooper, Edwin Bickford↗
NASA NTRS1992

Review of recent work on MPD thrusters at MIT

The topics are presented in viewgraph form and include the following: basic philosophy of MIT SSPL work; 2-D numerical magnetoplasmadynamic (MPD) simulations; analysis of MPD boundary layers; and ignition of MPD thrusters.

Hastings, Daniel↗
NASA NTRS1988

Cathode phenomena in a low power, steady state MPD thruster

Mass loss and surface temperature measurements, filter photography and SEM surface characterization are used to study cathode phenomena in a steady state self-field MPD thruster operated at power levels between 15 and 30 kW. The equilibrium cathode temperature is found to be approximately 3200 K over most of its length, for which evaporation and thermionic emission adequately explain measured erosion rates and current levels. The start-up phase is characterized by spot current attachment with associated high erosion rates.

Kelly, A. J.↗
NASA NTRS1992

Numerical simulation of geometric scale effects in cylindrical self-field MPD thrusters

A 2D, two-temperature, single fluid MHD code which incorporates classical plasma transport coefficients and Hall effects has been developed to predict steady-state, self-field MPD thruster performance. The governing equations and numerical methods of solution are outlined and discussed. Experimental comparisons are used to validate model predictions. The model accurately predicts thrust and reproduces trends in the discharge voltage for discharge currents below experimentally measured onset values. However, because the model does not include electrode effects the calculated voltage drops are significantly lower than experimentally measured values. Predictions of thrust and flow efficiency are made for a matrix of fifteen cylindrical thruster geometries assuming a fully ionized argon propellant.

Lapointe, M.↗
NASA NTRS1992

Numerical simulation of geometric scale effects in cylindrical self-field MPD thrusters

A 2-D, two-temperature, single fluid magnetohydrodynamic code which incorporates classical plasma transport coefficients and Hall effects was developed to predict steady-state, self-field magnetoplasmadynamic (MPD) thruster performance. The governing equations and numerical methods of solution are outlined and discussed. Experimental comparisons are used to validate model predictions. The model accurately predicts thrust and reproduces trends in the discharge voltage for discharge currents below experimentally measured onset values. However, because the model does not include electrode effects, the calculated voltage drops are significantly lower than experimentally measured values. Predictions of thrust and flow efficiency are made for a matrix of fifteen cylindrical thruster geometries, assuming a fully ionized argon propellant. A maximum predicted specific impulse of 1680 s is obtained for a thruster with an anode radius of 2.5 cm, a cathode radius of 0.5 cm, and equal electrode lengths of 2.5 cm. A scaling relation is developed to predict, within limits, the onset of cylindrical, self-field thruster instability as a function of geometry and operating condition.

Lapointe, M.↗
NASA NTRS1987

MPD thruster plasma instability studies

Results of an ongoing experimental/theoretical effort to understand the influence of plasma waves and instabilities upon coaxial plasma thruster performance and longevity are discussed. An experiment which permits measurement of the plasma dispersion relation plus a suite of plasma parameters for each one millisecond quasi-steady discharge is described. This investigation is guided by a linearized Boltzmann-Poisson kinetic numerical model which can accommodate the effects of collisions, inhomogeneities and the magnetic field. Preliminary tests reveal the presence of the low-frequency branch of an ion cyclotron wave. Although the stability of these waves still has to be established through spatial growth rate measurements, it is well known that they are prone to 'current-driven' instabilities. 'Current-driven' instabilities in the collisional tensor conducting plasma of the MPD thruster are analytically discussed and their relevance to the MPD plasma is illustrated by estimating a critical total current at which their onset occurs.

Kelly, A. J.↗