Posted on 07/29/2015 10:27:45 AM PDT by Red Badger
Two German researchers claim they have produced measurable amounts of thrust using a copy of NASA’s controversial EMDrive. It’s a result that has many people talking, but don’t plan your trip to the to the Alpha Centauri system just yet—the experts we spoke with are all highly skeptical of the study and its findings.
As reported in Hacked, the details of the new study are being presented this week by Martin Tajmar, a professor and chair for Space Systems at the Dresden University of Technology, and co-author G. Fiedler, at the American Institute for Aeronautics and Astronautics’ Propulsion and Energy Forum in Orlando. A copy of the study, which has yet to undergo peer review, has been made available prior to the conference: “Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects.” The Impossible Engine
Unlike conventional thrusters which need propellant, the electromagnetic drive, or EMDrive, works by converting electric power to thrust by bouncing microwaves within a closed container. But with no expulsion of propellant, there’s nothing to balance the engine’s momentum during acceleration; on paper, this device appears to violate conventional physics and laws of conservation of momentum. Hence the controversy. Critics of the EMDrive, of which there are many, say it’s all poppycock.
Earlier this year, scientists at the NASA Eagleworks advanced concepts lab performed an experiment in which a copy of the engine appeared to work within a vacuum—an intriguing result that rekindled debate, while also demonstrating the engine’s potential to work in space. As a recent post by David Hambling in Wired points out, the EMDrive could reach Pluto in just 18 months, as opposed to the 9-year trip taken by New Horizons.
The recent experiment by Tajmar and Fiedler was an effort to reproduce the Eagleworks results, also within vacuum conditions.
“Our measurements reveal thrusts as expected from previous claims after carefully studying thermal and electromagnetic interferences,” write the authors in their study.
Specifically, the researchers observed apparent thrusts of ~20 micro-Newtons at a low Q factor of <50. (In a resonator cavity such as the proposed EMDrive, Q factor gives information about the radiative leakage, linewidth, and other physical quantities of interest)
“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,” conclude the authors. “Nevertheless, we do observe thrusts close to the actual predictions after eliminating many possible error sources that should warrant further investigation into the phenomena.”
Looking ahead, the researchers say they’re going to conduct the experiment with improved magnetic shielding, perform further vacuum tests, and use “improved EMDrive models with higher Q factors and electronics that allow tuning for optimal operations.” Causes for Concern
While the latest results surrounding the EmDrive are certainly interesting, there are many reasons to remain skeptical.
“The microwave cavity thruster as set-up by Tajmar continues to violate momentum conservation and thus does not work as advertised,” says Eric W. Davis, a Senior Research Physicist at the Institute for Advanced Studies at Austin. “Why he doesn’t simply capitulate to that very obvious well-known issue in this particular application of electromagnetic physics is unknown to me. Maybe he is playing the role of the ‘supportive skeptic’ that wants to test this incredible outlandish EM propulsion claim for himself to see what it does.”
Davis says the German researchers have fallen into an experimental pitfall by claiming to have identified all “obvious” sources of systematic artifacts that could produce the tens of micro-Newton thrust signals that they measured. He accuses them of playing “word games” through their claims that there are other possible sources of systematic artifacts that remain untested, while at the same time insisting that they measured the same level of thrust reported in previous separate experiments by Sawyer, NASA’s Harold White (at Eagleworks), and a team of Chinese scientists.
Davis noticed some problems in the experiment as well.
“I noted in [the study’s] conclusion paragraphs that [Tajmar’s] apparatus was producing hundreds of micro-Newtons of thrust when it got very hot and that his measuring instrumentation is not very accurate when the apparatus becomes hot,” Davis told io9. “He also stated that he was still recording thrust signals even after the electrical power was turned off which is a huge key clue that his thrust measurements are all systematic artifact false positive thrust signals.”
“The experiment is quite detailed but no theoretical account for momentum violation is given by him, which will cause peer reviews and technical journal editors to reject his paper should it be submitted to any of the peer-review physics and aerospace journals,” Davis added.
NASA aerospace engineer Marc Millis tells io9 something similar. The experiment, Millis explains, seemed to show thrust lingering even after the power was off, which would be indicative of a thermal effect.
What’s more, when looking at previous EMDrive experiments, Davis noticed that the alleged thrust was generated slowly, and not instantaneously, when the electrical power was switched on.
“This is a direct indication of a thermal effect in reverse (heating versus cooling), which produces a clear false positive thrust signal,” says Davis. “Tajmar has to account for and reconcile this fact as well in his data analysis which he apparently did not discuss in his paper. This would be another nail in the coffin against the existence of any real definite momentum violating thrust produced in the microwave cavity.” Hype Engine
Davis points out that the researchers are not declaring any result that would definitively and positively substantiate previous experiments, and adds that he has little faith in these sorts of projects producing meaningful engines for future spacecraft. What’s more, he says, “my professional colleagues who all work in the space propulsion engineering business at the major aerospace corporations are not at all interested in any new electric space propulsion inventions or claims that can only produce thrust on the order of micro-Newtons (via devices that require high voltages and high electric currents and high E & M field strengths) because that magnitude of propulsive thrust is not applicable to any meaningful space mission propulsion needs.”
CalTech physicist Sean Carroll, who we’ve spoken to previously about the feasibility of an EMDrive, echoes Davis’ sentiments.
“My insight is that the EMDrive is complete crap and a waste of time,” Carroll tells io9. “Right there in the abstract this paper says, ‘Our test campaign can not confirm or refute the claims of the EMDrive’, so I’m not sure what the news is. I’m going to spend my time thinking about ideas that don’t violate conservation of momentum.”
Note: An earlier version of this article incorrectly described Q factor as an electric charge. Rather it’s a dimensionless quantity related to resonators. Specifically, in a resonator cavity such as the proposed EMDrive, Q factor provides information about the radiative leakage, linewidth, and other physical quantities of interest.
Read the entire study at Aerospace Research Central: “Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects”. Note: This is not a peer reviewed journal.
I am skeptical of what a modified microwave can do here.
I suspect an idea that is begging for money / funding.
Who needs that when you can just use your Interrositer?
This strikes me as a "no true Scotsman" fallacy.
I was really looking forward to that 18 month slog to Pluto!
But...it has graphics.
Newton's Law - for every action there is an equal and opposite reaction.
Given that, wouldn't the top speed of any interstellar craft be limited to, or less than, the speed of whatever is coming out of the tail end of the craft?
Asked another way, if you have a rocket, in a vacuum, with an exhaust speed of 15,000mph, would the rocket be able to travel faster than 15,000mph?
You’re mixing up the terms ‘speed’ vs. ‘acceleration’.
Constant acceleration will yield an increase in speed, even if slowly accelerated....................
Thanks for the information, especially the link.
It`s true.
When I turn on my microwave, the flat round thing inside goes `round and `round and never stops until I turn it off or set the timer.
They are skeptical and rightly so until one of these things gets off the ground which may well happen. It is about time in the technology evolution cycle for such a breakthrough.
1 N is the force of Earth's gravity on a mass of about 102 g = (1⁄9.81 kg). On Earth's surface, a mass of 1 kg exerts a force of approximately 9.81 N [down] (or 1.0 kilogram-force; 1 kgf = 9.80665 N by definition).
From the article:
the researchers observed apparent thrusts of ~20 micro-Newton
So we're not talking much 'force' of acceleration here.................
“The microwave cavity thruster as set-up by Tajmar continues to violate momentum conservation and thus does not work as advertised,” says Eric W. Davis, a Senior Research Physicist at the Institute for Advanced Studies at Austin.
What hogwash. Sure, it appears to be in violation of conservation of momentum, but if it works experimentally, then obviously that is not an impediment. Perhaps the law is not actually violated somehow, or the law is not as inviolable as we suspected (if the device works).
It may be a ‘quantum’ device. If so, then the Newtonian Laws go out the window..................
Not confirmed? Well, so much for the V3.
I’ve noticed my microwave turntable turns in opposite directions every time I turn it on..............I guess that way it is and ‘equal and opposite reaction’..................
“Given that, wouldn’t the top speed of any interstellar craft be limited to, or less than, the speed of whatever is coming out of the tail end of the craft?”
Well, what needs to be equal is not the velocities but the forces, and the force equals the mass times the acceleration.
So, a spacecraft generally shoots particles of very small mass at high acceleration out the back of the ship, which generates an equal force towards the front of the ship. However, because the ship is much more massive than the particles of propellant, the acceleration of the ship is much less than the acceleration of the particles.
Now, since spacecraft operate in a vacuum, the velocity will increase as long as they maintain that acceleration. Really, the velocity is limited by practical limits, like how much fuel the craft can carry, or whether the craft gets assistance from gravity using maneuvers to accelerate. As a certain point, there would be a hard limit to acceleration, as you approach the speed of light, but we can’t get anywhere near that, so it’s pointless to worry about.
I think that the EM Drive may move along a similar path but at a more rapid pace. As positive experimental results accumulate, they will be disputed by naysayers. Yet, assuming that the science is valid, preliminary working devices will soon follow and be tested in orbit, by NASA, and perhaps the Chinese, the European Space Agency, the Russians, and the Indians. In addition, tech titans Google and Apple are both sitting on immense stockpiles of cash and aching for new tech fields to conquer.
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