The highly controversial EmDrive is back to beguile scientists with a brand new round of experiments. They're documented in a new paper called "Direct Thrust Measurements of an EmDrive and Evaluation of Possible Side-Effects," given Monday at the American Institute of Aeronautics's Propulsion and Energy Forum in Orlando.
Led by professor Martin Tajmar, chair of Space Systems at the Dresden Technical University, the paper echoes the findings of previous experiments on the propellantless-propulsion system: In short, the thing seems like it works, and no one's really sure how or why.
Proposed back in 2001 by British engineer Roger Shawyer via his company Satellite Propulsion Research, the EmDrive is little more than a bell-shaped chamber into which microwaves are fired. The electrically-generated microwaves then bounce around inside the chamber, which is shaped in a way that's meant to create a difference in radiation pressure that then produces thrust, albeit in very, very tiny amounts.
The device has been built and tested by scientists in several countries including the US and China, and in each case the results show some amount of thrust being generated
If that sounds strange it's because it is—the device has been built and tested by scientists in several countries including the US and China, and in each case the results show some amount of thrust being generated despite an inability on the part of the scientists to definitively explain why.
Several have called the whole project a bunch of hooey, largely because it seems to violate the fundamental physical law of conservation of momentum. Others, like Harold White of NASA, who also tested the device and submitted his results to the AIAA, disagree and say it might have to do with pressing against a "virtual plasma" of quantum particles that constantly appear and disappear from spacetime. Needless to say, that's a contentious claim.
A major part of this latest round of tests was to work out potential causes of interference in the testing process that could be behind the perceived creation of thrust. The team built a device in close cooperation with Shawyer, and tried testing the device in a vacuum for the first time. Using both a "Knife's edge" (basically testing the thrust of the device on one side of a balanced scale) and torsion balance test, they controlled for magnetic interference, heat from the magnetron that produces the microwaves, and other variables that could be throwing the results, but even then detected amounts of force that were in line with predictions.
The paper observes a much smaller amount of thrust than previous experiments—about 20 micronewtons—but they also note that the most recent experiments are much more sensitive and involved a higher degree of dampening. They even detected thrust when they weren't expecting to, during a test with the engine inverted meant as a control experiment.
"Our test campaign can not confirm or refute the claims of the EMDrive but intends to independently assess possible side-effects in the measurements methods used so far," the paper says. "Nevertheless, we do observe thrusts close to the actual predictions after eliminating many possible error sources that should warrant further investigation into the phenomena."
What's it all mean? Either this prototype propellant-less engine is creating the illusion of thrust based on some unaccounted-for variable that's carried over a series of tests by different groups of scientists, or the researchers have stumbled on an entirely new way of creating thrust that can't yet be explained.
Tajmar and his team say that all they've done with this latest paper is show that more tests are called for, if only to weed out further possible false positives. They close by pointing out that, even in the worst case scenario, the tests might help develop better ways of shielding thrust readings from magnetic fields.
That's certainly not as sexy as a groundbreaking new form of propulsion, but it's an example of the tediously rational chipping away at a problem that marks true scientific inquiry.