Department of Aerospace Engineering
2101 Glenn L. Martin Wind Tunnel
University of Maryland
College Park, Maryland 20742
Graduate Research Assistant
Space Power and Propulsion Laboratory
Phone: (301) 405-8562 | E-mail: epetro (at) umd.edu
Dissertation Topic – YouTube Video
Development of a Water-Propelled Helicon Thruster with Specific Impulse Control
Motivation and Background
Due to on-board fuel supply limits, electric propulsion (EP) systems enable advanced missions to the outer solar system that cannot be achieved with chemical propulsion. Helicon plasma generators are of interest to the EP community because they create denser plasmas than traditional ion sources and circumvent the erosion mechanisms that often limit thruster lifetime. The absence of internal grids and electrodes also allows for a wide range of propellants, notably including water vapor. Water vapor could be harvested throughout the solar system for refueling and has the additional advantages that it is easily handled and storable in liquid form.
The goal of this research is to design and test a helicon thruster with water vapor propellant that achieves performance levels suitable for deep space exploration missions (such as mN level thrust, specific impulse greater than 1000 seconds, and thrust efficiencies near or above 50%). There are three major components to this effort. The first step is to analytically model the performance of a stand-alone helicon thruster using water vapor, and compare with traditional propellants, such as argon or xenon. The next step is to investigate the performance gains that can be realized with a secondary ion acceleration stage. Such stages have been proposed before, but have not yet been investigated with water vapor propellant. Finally, the performance with and without the secondary stage will be evaluated through a laboratory prototype.
While other researchers have demonstrated that water vapor can be relatively easily ionized with a helicon source, the theory behind operation is incomplete. Thus we have developed a water vapor ionization model that predicts plasma characteristics such as the molecular composition and energies of ions created as a function of the electron energy. These plasma characteristics determine the achievable thrust and specific impulse. These and additional loss mechanisms in the helicon source have been incorporated into a power balance analysis in order to predict and optimize thruster efficiency.
Once the operation of the stand-alone thruster has been established, the impact of an ion acceleration stage will be assessed. It is hypothesized that an ion cyclotron heating stage, which energizes ions with resonant waves, could increase the specific impulse. A large-scale example of this principle is employed by the VASIMR engine. Thus a secondary objective is to design and implement an acceleration stage for a small-scale water vapor thruster. The physical dimensions of the stage and the strength of the confining magnetic field must be optimized for the ion characteristics, which will be established in the first phase of the research.