James Woodward's one of the old names in propellentless thrust --- he's been working on Mach Effect based systems for a long time now. His approach is my favourite of all the anomolous science thruster systems, because (a) he actually has a testable theoretical model to back up his experiments, and (b) he doesn't talk about it much; in the fairly rare interviews, he tends to be focused more on coming up with ways to disprove his experiments, rather than self-aggrandisement; which to my mind is the main mark of a serious scientist.
By which I mean to say, in the nicest possible way, that he's not an impartial observer when talking about this thing, so it's worth being careful about what he says.
As an electric propulsion engineer used to measure thrust in the uN range, what disturbs me much more than thrust levels close to the sensitivity threshold is the fact that thrust is only detected some 10-20s after the RF is turned on (figs 9,8,13).
I am rather confident that there is no physical time scale in the RF generation process that would account for a 10-20s ramp, and this would contradict their own report of the fast RF power stabilization.
It definitely looks like thermal drift; in fact, thermal drift is _always_ the first thing to suspect when you get strange measurements with a low thrust balance.
It appears as well that the authors have conveniently prepared an answer for this objection with fig.5 which attempts to mislead the reader by suggesting that the very slow evolution of the balance displacement is to be expected as an artifact of the combined effect of thermal drift and RF pulse onset. But conveniently, the time units are arbitrary so that hopefully nobody will notice that RF onset was assumed in that figure to have exactly the same characteristic time as the thermal drift... When all measurements actually show that RF power stabilizes much faster.
The group has been working five years in their own time in this small laboratory with shoestring budget. White has a day job in NASA and he and others are working with this project in their free time. To best of my knowledge - and correct me if I'm wrong - NASA only gave them $50,000 and a room in Johnson Space Center 2011. They don't seem to be involved in any other way but "NASA Eagleworks Laboratories" makes it sound like official NASA organization.
Their results are consistently close to the detection threshold of their sensors. They are always flirting with the measurement error.
I think your view reflects a misunderstanding of how NASA works. The vast majority of the research done at NASA is done by small teams working on shoestring budgets.
Where do you get the idea that they did all of this research on their own time?
I've linked to it before on HN, but NASA's grand road map document includes a section on testing advanced propulsion ideas, which is what this lab is doing.
NASA's involvement is minimal, in that the resources dedicated to it are minimal. But it would be wrong to take that as some sort of implicit disavowal by NASA.
Rather, it's probably just reflective of a reasonable approach to budget prioritization. "Show something good for a little before I give you a lot" is a common approach to budgeting for speculative R&D.
Argument #1: it violates Newton's Third Law of Motion.
Argument #2: every time they improve the test apparatus, the measured force declines and is "coincidentally" close to the measurement limits of the apparatus.
Argument #3: It was originally designed based on a misunderstanding certain principles of Physics. Now they are trying to find a new explanation for why it works. What are the odds that you misunderstand physics, design something based on that misunderstanding, and that it then works in a barely-detectable way due to "unknown mechanism"?
The arguments against boil down to "Any reactionless drive must by definition violate conservation of momentum." We shouldn't reject any scientific conclusion as unquestionable gospel, of course, but off the top of my head I'm not sure that I can think of any fact about the laws of nature that I consider more firmly established than "momentum is locally conserved". (I'm a physics professor, for the record.) Conservation of momentum is part of the bedrock of everything from relativity to quantum field theory, so if you throw it out, you'll need to come up with entirely different (seriously: entirely different) replacements for those theories that nevertheless manage to reproduce their hundreds of enormously successful predictions (to just as many decimal points). Again, it could be true! Keep an open mind! But if it is, then literally every discovery in (say) particle physics in your lifetime has been a fluke: just dumb luck. You can decide how to balance that likelihood against the evidence presented thus far in favor of the drive.
I'm really not sure what the argument against impossibility is, apart from a fervent longing for something of the sort to be real. (A longing that I share, for what it's worth.) They claim to have some data showing that something really is generating thrust, but as I recall some experiments have shown comparably large results in both the "actual test" and "control" conditions, so I'm not sure what to make of that evidence.
There's a claim that it's just basic physics of microwaves bouncing around. That one's nonsense; from the article, "Woodward likened explaining the results seen at NASA purely in terms of microwave pressure to arguing that you can accelerate a car by getting in the driver’s seat and pushing on the windshield."
As that suggests, the drive would violate conservation of momentum as we currently understand it. It would also violate conservation of energy. Because of relativity, there's no such thing as absolute velocity, so the thrust can't vary by velocity. Since kinetic energy is proportional to the square of the velocity, but the acceleration is constant for a constant energy input, there's some velocity at which you're gaining more energy than you're putting in.
So if it does work, it'd be radically new physics. But there are various ideas for how it might work, like Woodward's, which is derived from general relativity and involves an explanation of inertia; he's been working for decades on reactionless drive experiments based on that idea. We don't currently have a generally-accepted explanation of inertia, so who knows.
If you have an em-drive cubesat, just putting that (battery-powered, closed system) on a balance beam / torsion pendulum in a vacuum chamber is a more rigorous experiment than anything that's been done so far.
I know absolutely zero about rocket physics or quantum mechanics but isn't this a fairly easy and "cheap" thruster to prototype and test in actual space?
Nothing beats real world results, and this doesn't seem that hard to test. It might even be faster and cheaper than what's already been done, no?
At the extremely low level of thrust we're talking about here, I suspect it would be a lot harder to be certain about removing all sources of error if they did this in space. See also Pioneer Anomaly.
The article mentions that the test was ran at only 80W of power, surely that could be scaled up to a few thousand watts and a more appreciable result could be seen even with another ground based test?
It can be easily measured in the lab. When the effect keeps diminishing with better measurement, it's strongly suggestive of no effect. This paper seems to have some areas where the next round of tests could be obviously improved.
There's been breakthroughs in a fully quantified theory of how electromagnetics can be used to create propulsion reliably and at (still incredibly small but) orders of magnitude larger than prior designs provided by the aeronautics research team from the Northwestern Polytechnical University in Xi'an.
The research team published their breakthroughs in 2008, and excitingly, they've been highly reproducible.
If they feed electricity into the microwave horn, how strong is the induced magnetic field around the wires? Would that push against anything? How is that compensated for in measurements?
Sad to see this nonsense pseudoscience constantly making HN's front page. Whenever it appears I debunk it using the same post[1] (in short, conservation of momentum cannot be violated) but it keeps coming back. Looks like even highly intelligent people like HNers are easily fooled by pseudoscience.
(Evidence, of course, weighs very heavily against the EmDrive. But this sort of "it can't be doing that because that's against natural law" is just as unscientific.)
Part of the world has entered the post-truth age, the spirit of the times likes a good story better than the facts, and if you speak facts you'll be damned by them.
Just look at the article itself, doesn't actually say anything about the paper beyond confirming it's going to be publicated, the rest is just retelling the story up to now like there's much debate going on.
As far as I know, there are some extremely questionable measurements showing there is something there, theory to explain it that is for sure completely wrong, and now this paper that might be alright that is not totally ruling it out. And based of this people go "why must momentum be conserved???!"; It ain't pretty, but that's the world we live in.
[+] [-] david-given|9 years ago|reply
By which I mean to say, in the nicest possible way, that he's not an impartial observer when talking about this thing, so it's worth being careful about what he says.
[+] [-] binarycoffee|9 years ago|reply
It appears as well that the authors have conveniently prepared an answer for this objection with fig.5 which attempts to mislead the reader by suggesting that the very slow evolution of the balance displacement is to be expected as an artifact of the combined effect of thermal drift and RF pulse onset. But conveniently, the time units are arbitrary so that hopefully nobody will notice that RF onset was assumed in that figure to have exactly the same characteristic time as the thermal drift... When all measurements actually show that RF power stabilizes much faster.
[+] [-] dpark|9 years ago|reply
Even if you're right, assuming malice seems premature and pessimistic.
[+] [-] Nokinside|9 years ago|reply
The group has been working five years in their own time in this small laboratory with shoestring budget. White has a day job in NASA and he and others are working with this project in their free time. To best of my knowledge - and correct me if I'm wrong - NASA only gave them $50,000 and a room in Johnson Space Center 2011. They don't seem to be involved in any other way but "NASA Eagleworks Laboratories" makes it sound like official NASA organization.
Their results are consistently close to the detection threshold of their sensors. They are always flirting with the measurement error.
[+] [-] 0xffff2|9 years ago|reply
Where do you get the idea that they did all of this research on their own time?
[+] [-] snowwrestler|9 years ago|reply
NASA's involvement is minimal, in that the resources dedicated to it are minimal. But it would be wrong to take that as some sort of implicit disavowal by NASA.
Rather, it's probably just reflective of a reasonable approach to budget prioritization. "Show something good for a little before I give you a lot" is a common approach to budgeting for speculative R&D.
Edit: here's my earlier comment
https://news.ycombinator.com/item?id=10497100
[+] [-] sfifs|9 years ago|reply
[+] [-] jsprogrammer|9 years ago|reply
If the NASA name is being used unofficially in such a public manner, wouldn't NASA do something about it?
[+] [-] danielmorozoff|9 years ago|reply
Actual paper: https://drive.google.com/file/d/0B7kgKijo-p0ibm94VUY0TVktQlU...
[+] [-] jchung|9 years ago|reply
I think at this point, I'm resigned to waiting for an emdrive cubesat to just prove it once and for all: http://www.popularmechanics.com/science/energy/a22678/em-dri...
[+] [-] cjensen|9 years ago|reply
Argument #1: it violates Newton's Third Law of Motion.
Argument #2: every time they improve the test apparatus, the measured force declines and is "coincidentally" close to the measurement limits of the apparatus.
Argument #3: It was originally designed based on a misunderstanding certain principles of Physics. Now they are trying to find a new explanation for why it works. What are the odds that you misunderstand physics, design something based on that misunderstanding, and that it then works in a barely-detectable way due to "unknown mechanism"?
[+] [-] Steuard|9 years ago|reply
I'm really not sure what the argument against impossibility is, apart from a fervent longing for something of the sort to be real. (A longing that I share, for what it's worth.) They claim to have some data showing that something really is generating thrust, but as I recall some experiments have shown comparably large results in both the "actual test" and "control" conditions, so I'm not sure what to make of that evidence.
[+] [-] DennisP|9 years ago|reply
As that suggests, the drive would violate conservation of momentum as we currently understand it. It would also violate conservation of energy. Because of relativity, there's no such thing as absolute velocity, so the thrust can't vary by velocity. Since kinetic energy is proportional to the square of the velocity, but the acceleration is constant for a constant energy input, there's some velocity at which you're gaining more energy than you're putting in.
So if it does work, it'd be radically new physics. But there are various ideas for how it might work, like Woodward's, which is derived from general relativity and involves an explanation of inertia; he's been working for decades on reactionless drive experiments based on that idea. We don't currently have a generally-accepted explanation of inertia, so who knows.
[+] [-] dTal|9 years ago|reply
[+] [-] ComputerGuru|9 years ago|reply
Nothing beats real world results, and this doesn't seem that hard to test. It might even be faster and cheaper than what's already been done, no?
[+] [-] semi-extrinsic|9 years ago|reply
[+] [-] joezydeco|9 years ago|reply
http://www.ibtimes.co.uk/space-race-revealed-us-china-test-f...
[+] [-] amiga-workbench|9 years ago|reply
[+] [-] huragok|9 years ago|reply
[+] [-] andygates|9 years ago|reply
Time for me to break out the Tech Readiness Levels: this proposal is TRL 0 (1 if you're a True Believer). Observe the TRL required by NASA for a flying prototype. https://en.wikipedia.org/wiki/Technology_readiness_level
[+] [-] jwtadvice|9 years ago|reply
The research team published their breakthroughs in 2008, and excitingly, they've been highly reproducible.
Unfortunately, the paper appears to be behind a paywall: http://en.cnki.com.cn/Article_en/CJFDTOTAL-YHXB200805027.htm
Does anyone on HN have the background necessary to explain the mechanics of EM propulsion to laymen?
[+] [-] unknown|9 years ago|reply
[deleted]
[+] [-] jwatte|9 years ago|reply
[+] [-] unknown|9 years ago|reply
[deleted]
[+] [-] maverick_iceman|9 years ago|reply
[1] http://www.preposterousuniverse.com/blog/2015/05/26/warp-dri...
[+] [-] FeepingCreature|9 years ago|reply
Do not tell nature what it can and cannot do.
(Evidence, of course, weighs very heavily against the EmDrive. But this sort of "it can't be doing that because that's against natural law" is just as unscientific.)
[+] [-] dbingham|9 years ago|reply
[+] [-] tombone12|9 years ago|reply
Just look at the article itself, doesn't actually say anything about the paper beyond confirming it's going to be publicated, the rest is just retelling the story up to now like there's much debate going on.
As far as I know, there are some extremely questionable measurements showing there is something there, theory to explain it that is for sure completely wrong, and now this paper that might be alright that is not totally ruling it out. And based of this people go "why must momentum be conserved???!"; It ain't pretty, but that's the world we live in.
[+] [-] dokem|9 years ago|reply
[+] [-] outworlder|9 years ago|reply
Why?
[+] [-] pklausler|9 years ago|reply