Improved Microwave Electrothermal Thruster Systems for Satellites and Space Flights

  • Published
  • By Maria Callier
  • Air Force Office of Scientific Research
ARLINGTON, Va. --  Air Force-supported Microwave Electrothermal Thruster (MET) research that began at Pennsylvania State University may lead to higher performing miniaturized electric propulsion systems for satellites. This would mean improved satellite maneuverability, endurance, fabrication and testing of a space flight ready microwave thruster system.

Engineering professor, Dr. David Micci and his research team originally used a thruster that operated off a microwave generator, which creates a plasma (without electrodes) within an area that heats a propellant gas and that in turn causes nozzle expansion. This technology is used in weather radar, aircraft radios and other communications applications.

At 2 inches long, 1.25 inches in diameter and with 100-watts of power, the MET generated the highest thrust for a low power electrothermal thruster. Although it operated ineffectively in the beginning, there was much excitement to herald its beginning.

In a Science Daily article published at the time, Micci explained, 'The new mini-microwave thruster has the potential not only to reduce on-board power requirements, but also to extend a satellite's productive life since it requires only one third the amount of propellants used by other systems.'

The article also noted that the MET was safer than chemical-based systems because the thruster only operated when the magnetron produced a microwave. If the magnetron was turned off, the plasma that heated the fuel was inoperable as well.

Fortunately, continued MET research funded by Northrop-Grumman has resulted in higher performance than what is currently available for satellites' arcjets.

The team has focused their work on storable propellants like hydrogen, nitrogen, ammonia, helium, hydrazine and water. They have most recently been looking at the optimization of a thruster operation at 8 GHz and 350 watts of microwave power and that has doubled the chamber temperature with an ammonia propellant.

"As performance increases, nozzle temperature is increasing, leading to the melting of our currently used nozzle materials," said Micci. "A search is now underway to identify other nozzle materials, either metal or ceramic, that have all the necessary characteristics: high melting temperature, sufficient structural strength and low thermal conductivity."

The MET has been tested on the ground so far, but Micci's aim is to see it in operation in space, and so he plans to take the research one step further by designing and fabricating a space flight-ready microwave thruster system.