Molecular dynamics Poiseuille flow simulations were conducted with diffuse, one-zone, two-zone, and three-zone wall models for tubes containing argon or nitrogen for tube radii from 20 to 65 Å at both sub- and supercritical temperatures. The diffuse wall showed some variation from the analytical velocity profile in the tube, whereas the explicitly modeled walls performed very well. All wall models were able to maintain system temperature to reach the desired simulation conditions. The diffuse wall failed to capture the nanoscale behavior of the flow. The explicitly modeled walls performed very well at the nanoscale but determining the appropriate fluid-wall interactions is critical.

Direct thrust measurements of an 8-GHz microwave electrothermal thruster were performed. Experimental work involved the redesign of the thruster cavity to minimize its weight and the construction of a vertical thrust stand. Thrust measurements were made using ammonia and simulated hydrazine (50% and 100% decomposed) as propellants. Testing was performed over a range of 100-250 W of microwave power input into the thruster. For all three propellants, the thrust increased with the increasing mass flow at higher microwave power levels able to sustain plasma at higher flow rates. Ammonia specific impulse increased with increasing cavity input power, reaching 264 s at 250 W. The 50% and 100% simulated decomposed hydrazine exhibited an initial increase in specific impulse with increasing power; however, further increases in power did not result in increased specific impulse. Higher levels of thrust and specific impulse at the same microwave input power were measured for the 100% decomposed simulated hydrazine compared to the 50% decomposed due to the absence of ammonia in the 100% decomposed hydrazine.

This paper discusses the current research status of the MET (Microwave Electro‐Thermal) thruster. In the MET thruster, an electrodeless, vortex stabilized, plasma is produced in a microwave resonator cavity for the purpose of heating gaseous fuel to produce a high temperature rocket exhaust for space propulsion. The higher specific impulse (momentum transfer per unit weight) of these heated gases offers advantages over traditional chemical rockets in terms of reduced fuel mass. In MET devices, dense plasmas have been produced in various possible fuel gases, nitrogen, hydrogen, and ammonia, using 600 to 2200 Watts of microwave power at a frequency of 2.45 GHz. Ammonia has been found to give a specific impulse of 550 sec. It has been found that the plasma is a 98% absorber of microwave power leading to negligible reflection of power back to the microwave source and making the cavity operate at low Q. Taking advantage of this effect, it has been found that a very compact MET thruster design could be operated, with the magnetron microwave source and resonator cavity joined in one unit. The MET can run at a variety of power levels and use many fuels, including H2O.