News headlines are buzzing with headlines such as “Scientists Confirm ‘Impossible’ EM Drive Propulsion” (Hacked) and “‘Impossible’ propellantless engine appears to work” (Sydney Morning Herald).
At a July Propulsion and Energy Forum held by the American Institute for Aeronautics and Astronautics in Orlando, Florida, two researchers (Tajmar and Fiedler) have presented a paper (paywalled, abstract) whose results are suggestive of a replication.
According to the paper’s abstract:
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.
It’s worth noting that the paper has not yet undergone peer review, and that those of us on the outside don’t really have anything new to go on since the science-by-Internet-forum release earlier this May.
[…]all that outside researchers really have to go on is the NASASpaceflight.com forum, which includes a thread of posts stretching back several years, discussing the development of the EmDrive. […]It’s unclear from these forum posts if the prototype propulsion system actually generated any thrust during the recent tests, said Ethan Siegel, a physics and astronomy professor at Lewis & Clark College in Portland, Oregon. Siegel also wrote about the EmDrive in Forbes Magazine, to which he regularly contributes.
Siegel said he is seeing claims of thrust happening just a few times over many tests, with a frequency that is “not inconsistent with random chance.” Further, the thrust that was produced in these rare instances was apparently just above the margin of error for measurement, he added.
One of the major hurdles facing propellantless propulsion claimants is Newton’s Third Law of Motion (You may remember the Third Law from an earlier, recent rant by this DN contributor). Over-simply stated, a propulsion method that doesn’t generate force by accelerating mass has some theoretical explaining to do regarding its momentum. Its novelty is without question (and might rewrite/expand physics if it pans out), but it doesn’t have the reliable track record of other rocket-alternatives.
Some other drive types that NASA (and partners) really are working on
Solar sails: These devices unfold to reveal a massive surface area whose purpose is to collect photons. While photons are generally considered mass-less, they still carry momentum. It’s this momentum that the solar sail borrows, as it slowly accelerates through the vacuum of space. Some readers may be familiar with the Planetary Society’s recent crowdfunded lightsail mission.
Ion thrusters: An ion thruster creates thrust by electrostatically accelerating ions. These guys are very slow to accelerate, but have a high efficiency (specific impulse, or ISP). They also look really cool. In fact, they’re so neat-looking, much of the news coverage of the propellantless drive claimants’ paper has snagged the below image of a Hall effect thruster from NASA/JPL!