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China's Radical New Space Drive
First time accepted submitter Noctis-Kaban writes "Scientists in China have built and tested a radical new space drive. Although the thrust it produces may not be enough to lift your mobile phone, it looks like it could radically change the satellite industry. Satellites are just the start: with superconducting components, this technology could generate the thrust to drive everything from deep space probes to flying cars. And it all started with a British engineer whose invention was ignored and ridiculed in his home country."
The principles behind the EmDrive have serious theoretical problems, and the original builder and designer never tested it in a vacuum chamber.
Taking a sealed container and pumping a few kilowatts of microwaves into it, chances are any thrust developed is actually air that's getting heated up and expanding out of the container. Unless the EmDrive has been put in a vacuum chamber where this can be demonstrated to definitely not be the case (i.e. low enough that their couldn't be enough reaction mass) then it's not actually working.
The most inviolable law in the universe is that everything flies pointy end first.
“He’s not deformed, he’s just drunk!”
From the article: "Seems to violate law of conservation of momentum". - Yup it does. Imagine putting an invisible mass-less box around the entire system. Almost nothing comes out the back (only microwave energy - more on that later). The center of mass of the box accelerates. This is a violation of conservation of momentum - one of the most well understood and best tested laws in physics. If there were some exotic high energy physics effect proposed for this at least it might be worth listening, but this is just electromagnetism - very well understood. The "group velocity / phase velocity" is just jargon that has nothing to do with this since it is the Poynting vector that carries momentum.
You CAN make a reaction drive using photons (microwaves in this case), this idea has been around for many decades. The problem is that photons carry a lot of energy relative to their momentum so it takes an enormous power source to produce any thrust. So far no one has found a practical application where there was a large enough energy (and high enough power ) source to make this practical.
There have been a lot of experiments with microwaves - I've personally worked on a 600MW pulse microwave system. There have even been attempts at microwave driven spacecraft sails. Some early experiments seemed to indicate more thrust than would be expected from momentum conservation. Eventually this was tracked down to gas absorbed on the surface being heated and released by the microwaves - essentially a conventional rocket. With very high microwave powers you can generate forces in all sorts of ways in a closed laboratory environment that would not work in space.
This will not work.
No more Anonymous Coward posts? Whatever shall we do?
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
The FAQ deals with conservation of momentum, allowance for bouyancy, electromagnetic effects, convection and other issues here: http://emdrive.com/faq.html. A fantastic picture of the device on this page: http://emdrive.com/.
Here are some of the FAQ answers:
Q. Why does the EmDrive not contravene the conservation of momentum when it operates in free space?
A. The EmDrive cannot violate the conservation of momentum. The electromagnetic wave momentum is built up in the resonating cavity, and is transferred to the end walls upon reflection. The momentum gained by the EmDrive plus the momentum lost by the electromagnetic wave equals zero. The direction and acceleration that is measured, when the EmDrive is tested on a dynamic test rig, comply with Newtons laws and confirm that the law of conservation of momentum is satisfied.
Q. Are there any convection currents which might affect the results?
A. Convection currents did not affect the results, as measurements were taken with the thrust vector up, down and horizontal. Test runs were also carried out using a thermal simulation heater to quantify the effects of change of coolant temperature.
Q. Have electromagnetic effects been taken into account? These include interactions between current-carrying conductors and between such conductors carrying RF currents and nearby metallic structures in which currents might be induced.
A. Stray electromagnetic effects were eliminated by using different test rigs, by testing two thrusters with very different mounting structures, and by changing the orientation by 90 degrees to eliminate the Earth’s magnetic field.
experiment (since IANAP), I do want to say that there seems to be a troubling trend amongst the best and the brightest in many STEM fields to mistake theory for reality. Theory is great and proceeds under the scientific method from empirical observation, but as we've seen throughout history, new phenomena and corner cases to arise and require theory to be amended.
It's fine to say "this is clearly unlikely to work under current theoretical understandings" but let's also refine and do the experiments to the best of our ability so that science remains scientific (i.e. nominally empirical and ultimately practical in nature). There's a difference between taking "current theory suggests this is likely to fail" as a statement of fact and mistaking theory instead to be *evidence* about experimental outcomes.
No theoretical argument can be evidence for the reality or unreality of phenomena, no matter how well-formed. That's not to say that we ought to mistake the phenomena at issue—it's obviously critical to be able to understand, rather than misconstrue, the reality that we observe—only that sometimes a generation or two of scientists seem to get complacent and imagine that they've got the world all figured out after all.
Let's continue to do, and—to the best of our ability and within reason (but with "within reason" here broadly defined—allocate resources for, actual experimentation and empirical observation of the world around us.
Not that we don't—but to my eye, the attitude that if theory doesn't support it, it's always a waste of money to test it out experimentally, is a dangerous one for the future of a science that is far less uniform, linear, and accumulative in its progress than we often tend to remember.
STOP . AMERICA . NOW
It blatantly violates conservation of both momentum and energy. It's advertised as being useful for spacecraft propulsion, changing the momentum of the spacecraft without emitting anything that would carry equal momentum in the opposite direction. If Shawyer's claims were true, an EmDrive placed on end in a gravity field would be either an energy sink or source (depending on orientation) with infinite capacity. I see no reason why anything else on the site should be treated as any more trustworthy.
From my perspective, Einstein muddied the entire subject by equating reality with what is observed and using that false premise
The new scientific method is here! Make some wild guess about how the universe must work because that's how you'd like it to work, then call all previous work foolish and flawed. Done. Wait, didn't we used to do something similar to that?