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China Claims Tests of 'Reactionless' EM Drive Were Successful (popsci.com)
An anonymous reader quotes a report from Popular Science: The "reactionless" Electromagnetic Drive, or EmDrive for short, is an engine propelled solely by electromagnetic radiation confined in a microwave cavity. Such an engine would violate the law of conservation of momentum by generating mechanical action without exchanging matter. But since 2010, both the United States and China have been pouring serious resources into these seemingly impossible engines. And now China claims its made a key breakthrough. Dr. Chen Yue, Director of Commercial Satellite Technology for the China Academy of Space Technology (CAST) announced on December 10, 2016 that not only has China successfully tested EmDrives technology in its laboratories, but that a proof-of-concept is currently undergoing zero-g testing in orbit (according to the International Business Times, this test is taking place on the Tiangong 2 space station). If China is able to install EmDrives on its satellites for orbital maneuvering and altitude control, they would become cheaper and longer lasting. Li Feng, lead CAST designer for commercial satellites, states that the current EmDrive has only a thrust of single digit millinewtons, for orbital adjustment; a medium sized satellite needs 0.1-1 Newtons. A functional EmDrive would also open up new possibilities for long range Chinese interplanetary probes beyond the Asteroid belt, as well freeing up the mass taken up by fuel in manned spacecraft for other supplies and equipment to build lunar and Martian bases. On the military side of things, EmDrives could also be used to create stealthier, longer lasting Chinese surveillance satellites.
I think the bottom line is nobody still knows how it works, which is both fascinating and scary at the same time. If it works how some scientists think it works, that would indeed rewrite the laws of physics as we know them -- and this is scary. But since early indications show it working it is extremely fascinating since it opens up so many new possibilities. It also gives new material for science fiction writers to work on.
I would like to see them be able to scale this up and boost its performance, and of course explain just how exactly it works. The one thing that bothers me with this drive is that it requires a somewhat large amount of energy to work, how would we be able to produce that energy if we were to think for example of sending probes outside our solar system? Solar power won't really cut it that far away and nuclear power plants have a limited lifespan, plus they add a lot of weight to the probes, which would nullify the EM drive's point to some extent.
I followed one of the links, and got a picture claiming to be a 'test' at Eagleworks, and the words 'in air' (without saying exactly what is in air).
Look, the heat sink for the power amp is mechanically linked to the large end of the cavity... Doesn't it seem to anyone with even a tiny bit of experience with simple air convection from a bigass heat sink that this is the exact configuration you'd most expect to exhibit such effects, and of the reported size too?
Eagleworks are apparently smart people... what is this picture supposedly showing?
Trouble is that's super expensive. There are two choices here:
1. The EM drive works, which means there is a substantial gap in the laws of physics which have already passed very many far, far more stringent tests than the one in this article, implying thousands of other unrelated experiments were flawed in a consistent way.
2. The EM drive doesn't work and there was a flaw in this and a rather tricky experiment.
If you're about to blow a spaceship's worth of cash on something, you might first want to consider how tricky the experiment is. Putting in a kilowatt (think domestic microwave) and measuring a milinewton (a grain of rice?) is hard. Think of all the confounding factors. Now consider none of the other tests have stood up to peer review yet.
Which do you think is more likely now, 1 or 2?
And would that influence your decision to blow a few tens of millions on it?
SJW n. One who posts facts.
Just because perpetual motion can't exist, doesn't mean there can't be, and aren't, things that come so close as makes no difference to humans.
You're standing on one right now.
Sure the earth can't spin forever. But it will be spinning long after we're extinct. It's a perpetual motion machine for all practical concerns.
The universe is literally filled with those.
And we can and have built machines to harness some of the energy from those things movements.
A tidal-wave power-generator is actually pretty close to a perpetual motion machine - since it generates power based on the gravitational pull of the moon. The moon is not going to run out of momentum and stop rotating around the earth in any time soon enough to matter to humans. It's as close to a perpetual motion machine as makes no difference. And we've harvested it's power - already. There's your gravity powered machine - that will run until it breaks down.
It may not be "perpetual motion" as we normally think of it, but it's as close as makes absolutely no difference. And we've just scratched the surface of what we can do when we harvest gravitational motion to power machines (partly because it's very hard - it's probably impossible to do a cyclic machine using earth gravity, but as the tidal wave generator shows - it can be done using the moon's gravity - which already varies cyclicly). Whose to say we won't find a way to have The motion of Jupiter provide the energy to get our next probe too Jupiter ?
It would be very hard and I have no idea how it could work - but there is nothing in the laws of physics that says it can't be done. It's not creating energy. It's not failing to conserve momentum. It's not lacking an existing energy source - it's just using one that is very hard to use and which we've only just started figuring out how to use (sufficiently so that I'm pretty sure the tidal wave generator is the ONLY example of a genuine gravity powered machine - but it's early days).
For all we know that's what the EM-drive is doing, it may be pushing against gravitons and propelled by "gravity" itself.
Unicode killed the ASCII-art *
And why would the 'torch engine' not become an over-unity device?
I'm glad you asked! And it turns out you can't entirely ignore relativity.
So, as you correctly pointed out, the thrust is constant, so the (non relativistic) speed increases linearly, but the energy goes quadratically.
Since the power in is constant, eventually the power due to the increasing k.e. must exceed the power in. The smaller the thrust, the higher the speed at which the cross over occurs, but crossover must occur.
Well, yes, except there's a speed limit: the speed of light. It turns out that if you crunch the maths right then for the tiny thrust from the photon drive (3uN/kW), the breakeven speed is the speed of light.
You can never reach that so you can never reach the breakeven point and you certainly can't exceed it.
For anything (the EM drive) claiming a higher thrust per unit of power, the breakeven point is below c, so you could theoretically exceed it, yielding free energy.
SJW n. One who posts facts.
Of course, that requires assuming a great deal about the actual performance characteristics of the device. At present we only have evidence that it generates a particular thrust when basically at rest with respect to local inertial reference frames, though the exact details of its orbital behavior may shed more light on that. If it's reacting against virtual particles, dark matter, space-time curvature, aether, or any number of other things that might have specific localized properties, then it's thrust/watt ratio might well diminish with speed to remain under the "perpetual energy" exploitable limit.
And there's also the (arguably less plausible) possibility that it's actually tapping into some outside source of energy that we simply do not yet recognize. As one example, the quantum vacuum potentially contains truly astounding energy density, and while it's generally accepted that the energy could not be directly tapped, it's far from proven. This device might conceivably in some sense be erecting a directional electromagnetic "sail" into a normally unperceived energy source, with the kinetic energy gains coming not from the energy required to maintain the sail, but from the interaction of that sail with whatever energetic medium it's in contact with.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
I strongly recommend reading Shawyer's various papers on the drive (most can be found at www.emdrive.com). Now I will admit that I find quite a lot of their contents either incomprehensible or just plain crazy, but he does evolve some equations which relate thrust to input power, velocity (usually zero in these tests) and (vitally) the Q of the cavity.
He claims (and I certainly haven't bothered to verify this) that if you look at the various papers reporting experimental tests and take into account their reported Q values then they all match his equation to within experimental error. So, he claims that the reported thrusts do 'overlap' if you allow for the different Qs being achieved.
There is no problem with any data anywhere in the universe that can't be fixed by applying one of finaglers constants.
Examples of these constants: FC0 = (Data observed - answer wanted), FC1 = (Data observed / answer wanted) etc etc More complicated with more data points obviously.
The whole idea of dark matter is simply the application of FC1. Matter is missing, so it must be dark.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'