Magnetoplasmadynamic Research Articles

Electric propulsion in Europe

This paper presents the major activities carried out in Europe in the field of Electric Propulsion. Four lines of development are presently pursued. Two different models from the RIT family of radio-frequency ion thrusters are being developed in Germany. The RIT-10 thruster, operating in the thrust range of 10 mN, is due to be flight tested on board of the European Retrievable Carrier EURECA in 1988. A scaled-up version of this thruster, the RIT-35, is under development and it is mainly intended as the basic element of an Electric Propulsion Module for future interplanetary missions. Field Emission Electric Propulsion (FEEP) and Magneto-Plasma Dynamic (MPD) thrusters are also undergoing extensive research and testing. The paper describes the research, development and qualification programmes associated with the electric propulsion systems mentioned above and the work done by European industries and Universities. Finally an account is given of future interplanetary missions for which the use of primary electric propulsion is envisaged.

Self-field MPD thruster with atomic and molecular propellants

This study is devoted to the design, the operational characteristics and optimization of a self-field magnetoplasmadynamic (MPD) arc in view of its applications as a thruster and as a plasma source for recombination lasers. Its principal characteristics, i.e. its terminal voltageVE1and the exhaust speedueas functions of the square of the discharge currentI divided by the mass flow ratem are determined experimentally for atomic propellants. On the basis of measured diagramsVE1versus (I2/m) our discharge configuration is found to be well comparable to those applied by other laboratories. However, in order to further increase the specific impulse, these devices should make use of propellants of low molecular weight. Therefore, we also show that these thrusters can be operated in a quasi-steady mode for atomic as well as for molecular propellants, e.g. H2, N2, O2. Existing theories and interpretations of observations on atomic propellants are reviewed and, if possible, extended to explain the experimental results obtained with molecular propellants. In the framework of these extended theories the high-power limit of a stable operation is well understood.

MPD arcjet system performance test

A new MPD (magnetoplasmadynamic) arcjet system was developed and tested to demonstrate its technological readiness for flight model design. The MPD arcjet, of quasisteady type, was repetitively operated. In the endurance test, more than 10 5 shots were cleared in continuous operation. Some components cleared more than 10 6 shots. Cathode erosion was markedly reduced through the use of newly developed material. Thermal data were obtained which define the thermal interface between the spacecraft and the MPD arcjet system. Waste heat from the electrodes was found to be 20–30% of the input power and to vary with repetition frequency. No technological difficulties are foreseen for further continuation of repetitive operation.

ＭＰＤアークジェットシステム

The current status and future prospects of the magnetoplasmadynamic (MPD) arcjet system are described. Recent research activities on the chemical rocket and electric propulsion are discussed. The characteristics of various MPD arcjet systems including the Komaba-I system developed by the Institute of Space and Astronautical Science of the Tokyo University are analyzed. The applications of the MPD arcjet system to the satellite test, lunar mission, free flyer test, space station test, and heliospheric exploration are discussed.

Comparison of potential electric propulsion systems for orbit transfer

Electric propulsion concepts are compared on the basis of trip time for the low earth orbit (LEO) to geosynchronous earth orbit (GEO) mission. Resistojet, arcjet, magnetoplasmadynamic (MPD), pulsed inductive, and ion engine thruster concepts are included. The optimum (minimum trip time) value of specific impulse is found to be dependent upon the specific mission and system being considered. As expected, the devices which can deliver good efficiency at low specific impulses promise the fastest trip times. The solution for trip time and propellant mass for the constant power, continuous low acceleration orbit transfer problem (one way and round trip) is presented in nomograph form. The influences of mission Delta V, thruster efficiency, specific impulse, power, power and propulsion system mass, and payload mass are clearly illustrated.

Inductive Energy Storage for MPD Thrusters

The high thrust density of the self-field magnetoplasmadynamic (MPD) thruster makes it a promising candidate for many advanced space missions. The high power requirements of this thruster lead to its operation in a pulsed mode from an energy storage device. The system characteristics of an inductive energy storage circuit with a solar array power from 25 kwe to 400 kwe are considered, by solving the circuit equations for the inductor charge and discharge phases. Using simple analytic models of the circuit components, the total system efficiency and inductance are determined as functions of the array output power and circuit resistance. The total system efficiency increases with array power and is acceptable only for low values of circuit resistance, indicating that superconducting circuitry may be desirable. The optimum charge-discharge cycle changes fundamentally as the circuit resistance is decreased through a critical value dependent on the thruster operating characteristics.

Thermodynamic Properties and Hall Currents in MPD Accelerators

A study of the relationship between local thermodynamic properties, magnetic field strengths, and Hall currents in the arc region of magnetoplasmadynamic (MPD) accelerators is presented.

Pressure and Current Effects on the Thermal Efficiency of an MPD Arc Used as a Plasma Source

Measurements of arc voltage and energy loss to the cooled electrodes of a magnetoplasmadynamic (MPD) arc, operating without an applied magnetic field, were made at chamber pressures of 26 to 950 torr, argon mass flow rates of 0.08 to 44 g/s and current of 200 to 2000 A. The resulting arc thermal efficiency varied from 22% at a chamber pressure of 26 torr to 88% at 950 torr. Thermal efficiency was only weakly dependent on arc current. It is concluded that the MPD arc operating without an applied magnetic field and at higher pressure than normally used in thruster applications is a reliable and efficient steady-state plasma source.

Low environmental pressure MPD arc tests.

Tests of lithium and ammonia magnetoplasmadynamic (MPD) arc thrusters were conducted in the 15-ft-diam, 65-ft-long vacuum tank at NASA Lewis Research Center. The tank pressure was maintained at 3 X 10 ~ torr during lithium performance testing. The thrust efficiency varied from 10% at a specific impulse of 1000 sec to 70% at 5500 sec, in fair agreement with previously published results at three decades higher environmental pressure. The over-all efficiency of the thruster using ammonia propellant was found to improve with increasing mass flow rate and was almost as high as that of the lithium thruster for specific impulse less than 2500 sec. The degree of ionization of the ammonia MPD arc was studied both by spectroscopic means and by estimating the power available for frozen flow losses. At approximately constant specific impulse the degree of ionization, and hence frozen flow Josses, correlated with arc voltage and less strongly with magnetic field. The current distribution of the discharge of an ammonia MPD thruster was studied by means of Rogowski coils. It was found that, under a wide range of conditions, the arc current was concentrated into spokes rotating at a frequency in the hundreds of kilohertz range. Under the conditions studied, the frequency increased with increasing magnetic field or increasing arc current and decreased with increasing propellant flow rate.

Nonequilibrium ionization in magnetoplasmadynamic power generation - theory and experiment

Test results from a closed-loop magnetoplasmadynamic (MPD) generator experiment at gas temperatures in the range of 1000°-1100 °F are examined in the light of the theory of magnetoplasmadynamic electrical power generation with nonequilibrium ionization. The effective electrical conductivities measured under virtual short-circuit electrical load conditions in a segmented-electrodes constant-area-duct experiment when the magnetic field is applied, are compared with the thermal equilibrium ionization conductivities, which are calculated using electron densities derived from Saha's equation with the corresponding gas temperatures inserted. This comparison gives a verification of the presence of magnetically-induced nonequilibrium ionization in the MPD generator duct. Next, the energy balance equation is used to derive the electron temperature. The electron temperature is in turn used to calculate the resultant nonequilibrium electron density. This is done using two approaches. One approach uses an ion balance equation, which balances the rate of generation of ions by the hot electrons with the rate of loss of ions by recombination. The other approach derives the electron density from Saha's thermal equilibrium equation using the electron temperature instead of the gas temperature. The calculated nonequilibrium conductivities resulting from the use of these two approaches are compared with those obtained by experiment.

Extrathermal Electrical Conductivity Measurements in a Magnetoplasmadynamic Generator

A DETAILED description of the International Research and Development Co., Ltd., magnetoplasmadynamic (MPD) generator has been given previously1,2. On July 14, 1964, a series of power generation experiments with caesium seeding of the helium were undertaken. This series differed from the previously reported runs3 mainly in the generator and nozzle configuration and materials. To reduce end current leakage, the tantalum nozzle used previously was replaced by a boron nitride nozzle, the exit region of the generator lengthened by 2 in. and the interior of the diffuser inlet spray-coated with alumina. The generator channel was constructed from boron nitride in attempts to reduce the internal current leakage encountered previously with alumina3. Sixteen pairs of narrow (1/16 in. × 1/2 in.) tantalum electrodes replaced the five pairs of square (1/2 in. × 1/2 in.) electrodes used previously; the gap between the electrodes was large (3/16 in.), to reduce insulator and boundary layer electrical breakdown. Five pairs of tantalum pins (1/16 in. diam.) were used to monitor open circuit voltages, two pairs in the nozzle and three pairs in the generator exit region. Four static pressure tappings and three thermocouples were also located in the channel wall. During operation of the loop nozzle inlet gas temperatures in excess of 1,700° C were measured. The maximum channel temperature measured was 1,110° C with a corresponding flow velocity of 1,730 m/sec and a Mach number of 0.79.