NASA is currently researching both pulsed and continuous
forms of MPDs with hydrogen or lithium as a propellant. While attractive from an
efficiency standpoint, lithium is a condensable propellant and may coat
spacecraft surfaces and power arrays. MPD thrusters using noncondensable
hydrogen propellant will eliminate these concerns and provide higher exhaust
velocities than lithium-fueled thrusters. Glenn is currently developing
high-specific-impulse, megawatt-class, hydrogen-fueled MPD thruster technology.
Research at Glenn encompasses a combination of systems analysis, numerical
modeling, and high-power experiments that investigate pulsed versions of both
self-field and applied-field MPD thrusters. Testing for these thrusters has
demonstrated exhaust velocities of 100,000 meters per second (200,000,000 mph)
and thrust levels of 100 Newtons (22.5 pounds) at power levels of 1 megawatt.
For perspective, this exhaust velocity will allow a spacecraft to travel roughly
11 times the top speed of the space shuttle (18,000 mph).
