An ion engine that smashes the fuel efficiency record has been registered for an innovation patent. Inventor Patrick Neumann told University of Sydney student newspaper Honi Soit the drive could go to “Mars and back on a tank of fuel”, but its first application may be shunting networks of small satellites around in Earth orbit.
Neumann says the idea for the ion engine came to him as a third year student assisting a postdoc as part of a program to connect undergrads with real research. Neumann measured the speed of titanium ions released by a pulsed electric arc, similar to an arc welder. “The titanium was coming out at 20 kilometers per second [12.4 miles per second] and I thought 'you could use that for thrust',” he told IFLScience. In subsequent work Neumann proved his hunch right, eventually testing the suitability of 11 materials.
The results were dramatic. One measure of thruster efficiency is specific impulse, commonly called “bounce per ounce,” and is measured in seconds. The existing record is NASA's High Power Electric Propulsion (HiPeP) with 9,600 seconds, but fueled by magnesium Neumann's drive managed an estimated 14,600 seconds of specific impulse. He says “Other metals have lower efficiency, but higher thrust. So you would need more fuel to get to Mars, but could get there faster.”
Schematic of Dr Patrick Neumann's ion thruster. Credit: Neumannspace
Neumann says metal fuels have advantages besides efficiency. HiPEP uses Xenon, and as Neumann says, “Xenon is hard to source away from Earth.” Magnesium is found as olivine in asteroids, but Neumann has achieved promising results with titanium, aluminium and other widely used metals. Spaceships using his drive might find capturing fuel made from a dead satellite a handy way to refuel, cleaning up the space junk problem at the same time.
Ion thrusters such as the one that took Dawn to Ceres are only suitable for use in vacuums, and Neumann says even getting off the Moon or larger asteroids will remain a job for rockets. However, he says his drive could be suitable for lifting a spacecraft from low gravity objects like Mars' moons Phobos and Deimos.
“Using very rough, very early calculations we think 20 kilograms [44 pounds] of magnesium could get a 100 kilogram [220 pound] ship to Mars and back. It would take three to five years and there will be some weight for the craft, solar panels and communications, but we think there would be 20 kilograms left over for the payload,” Neumann told IFLScience. “With a higher thrust fuel in a Neumann Drive you could do it in nine to 11 months, but the fuel tank would be empty when you got there.” In the second case a return journey would require either scavenging material locally or parking fuel in Mars orbit, or on a refuelling station established at Phobos or Deimos, preparatory to the voyage.
Neumann says experiments with pulsed electric arcs on metals go back to the 1920s, and some of the data collected was useful to him in assessing what to test. This work was done with less than half the current he uses, and no one before him had tried using high current pulsed arcs for thrust.