Electric Propulsion

Electric propulsion devices have been used for applications such as station-keeping and orbit transfer, in place of chemical rockets, because they provide a higher specific impulse. Detailed studies are needed for improvement in performance and for assessment of spacecraft integration. Primarily, empirical experience has been the basis for design of these devices. Numerical methods are being developed that offer the possibility for optimization studies on the computer.

Investigators

• Douglas VanGilder, Graduate Student
• Iain D. Boyd, Associate Professor

Ion Thrusters

Ion thrusters achieve very high specific impulse by accelerating charged particles across a potential difference using electrostatic force fields. In our work we are considering a 30 cm diameter xenon thruster being developed under the NSTAR program that is directed by NASA.

The exhaust plume is being modeled using the direct simulation Monte Carlo (DSMC) and Particle-In-Cell (PIC) techniques. An effort is being made to integrate these two approaches to facilitate greater accuracy in modeling. These methods simulate the behavior of uncharged and charged particles respectively. The modeling will be validated through direct comparison of simulation results with experimental data being generated at NASA Lewis Research Center. (For more information about the current study see Ion Thruster Plume Simulation.)

Acknowledgments

Publications

• Boyd, I.D., "Monte Carlo Simulation of Neutral Xenon Flow in Electric Propulsion Devices,"Journal of Propulsion & Power, 1998.

Hall Thrusters

Hall thrusters use an axial electric field to accelerate ions, similar to ion thrusters. Combining a radial magnetic field with this generates an azimuthal Hall current. This current interacts with the radial magnetic field producing a volumetric (j x B) accelerating force on the plasma.

The exhaust plume is modeled by the combination of the direct simulation Monte Carlo (DSMC) and Particle-In-Cell (PIC) techniques.

Acknowledgments

Publications

• Boyd, I.D., "Computation of the Plume of the D55 Hall Thruster,"AIAA Paper 98-3798, July 1998.

• VanGilder, D.B. and Boyd, I.D., "Particle Simulations of the SPT-100 Plume,"AIAA Paper 98-3797, July 1998.

Arc-Jets

In terms of specific impulse, arcjets provide better performance than resisto-jets. Arc-jets operate by flowing gas through a low power arc. The simulation of flow through these devices requires implementation of high temperature kinetics models. In addition, modeling of plasma behavior is required. Our work has focused on simulation of hydrogen arcjets for which there is a large volume of detailed experimental data available against which models may be compared and calibrated. A new code based on the direct simulation Monte Carlo method has been developed that also includes simple modeling of the important plasma physics.

Acknowledgments

Publications

• Boyd, I. D., "Extensive Validation of a Monte Carlo Model for Hydrogen Arcjet Flow Fields," Journal of Propulsion and Power, Vol. 13, 1997, pp. 775-782.
• Boyd, I.D., "Monte Carlo Simulation of Nonequilibrium Flow in a Low Power Hydrogen Arcjet," Physics of Fluids, Vol. 9, October 1997, p. 3086.
• Boyd, I.D., Kannenburg, K.C., Kossi, K.K., Levin, D.A., and Weaver, D.P., "Modeling the Plume Contamination and Emissions of an Ammonia Arcjet,"AIAA Paper 98-3505, July 1998.

Resisto-Jets

The direct simulation Monte Carlo (DSMC) method has been used to model gas flow through small nozzles representative of resistojets. In these simple electric propulsion devices, gas is heated by flowing over resistively heated coils and is expanded through a converging-diverging nozzle. These DSMC results have been compared to experiments conducted at the Aerospace Corporation in Los Angeles, CA and at NASA Lewis Research Center in Cleveland, OH. The computational method captures the nonequilibrium effects in the flow field.(see Figure)

Acknowledgments

Publications

• Boyd, I.D., VanGilder, D.B., and Beiting, E.J., "Computational and Experimental Investigations of Rarefied Flows in Small Nozzles," AIAA Journal, Vol. 34, 1996, p. 2320.