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What we know about the EmDrive and Cannae Drive

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Re: What we know about the EmDrive and Cannae Drive

#111

Post by Bud »

Tossrock wrote: post #67
wbhart wrote: post #24

Comparing the Chinese results with the American results, it seems that raising the wattage by a factor of 50 raises the thrust by a factor of 15000. That's somewhat hard to believe. On the other hand, the linked pdf from the Chinese team suggests that at just 3 times the wattage of the American group, they got 1500 times the thrust. I think there is some confusion somewhere.

It seems like an impossibly basic mistake, but confusing micro- and milli- newtons would make the math a lot more reasonable.

Not impossibly basic at all. Space missions have failed because of these kinds of basic math errors:

http://www.wired.com/2010/11/1110mars-climate-observer-repor...

Re: What we know about the EmDrive and Cannae Drive

#112

Post by TheLoneWolfling »

danielweber wrote: post #97
mahranch wrote: post #58

Earlier quoted context omitted.

This is less like flush toilets and more like computers. It took nearly 50 years for the first computers to sit in consumer's home offices. It took time for the technology to be miniaturized and cheap enough to make its way to consumer electronics. Or even cell phones. We were using radio signals in hand held devices for nearly 50 years before a vast majority of consumers were walking around with phones in their pock…

If this were proven true, there would be a completely manic gold-rush of capital into the area. Flying cars that operate at less than 1/10th the energy of cars on the road now? This would very quickly move from "let's wait for NASA to do more tests" to "let's beat NASA to the test." That's all assuming it's real, of course. I'd bet against it.

Where are you getting that 1/10th number from?

The most thrust anyone was getting was 750mN at 2.5KW. At that efficiency you need to have something that produces >32.7W/g just to hold itself up. That's rocket engine territory: http://en.wikipedia.org/wiki/Power-to-weight_ratio

We barely have supercapacitors that'll deliver that sort of power output. For a few seconds, maybe. Not accounting for the mass of the device itself.

Hopefully if this ever turns out to be something the efficiency will improve. But I'm not holding my breath.

(Number taken from here: https://news.ycombinator.com/item?id=9474610 )

Re: What we know about the EmDrive and Cannae Drive

#113

Post by TheLoneWolfling »

hooo wrote: post #31

I'd really like this to be real. I think they need to precisely measure the mass of the whole device before and after the experiment, to make sure the thrust isn't coming from ionization or some decay.

They also need to check their vacuum.

There's a whole lot of power being thrown around inside those boxes.

Re: What we know about the EmDrive and Cannae Drive

#114

Post by Dylan16807 »

Steuard wrote: post #17
creamyhorror wrote: post #9

Earlier quoted context omitted.

According to physicist Harold White, leader of the NASA Eagleworks team, it can't simply be a "photon rocket": The NASASpaceflight.com group has given consideration to whether the experimental measurements of thrust force were the result of an artifact. Despite considerable effort within the NASASpaceflight.com forum to dismiss the reported thrust as an artifact, the EM Drive results have yet to be falsified. After c…

Yes, sure, they've measured something surprising. I have no reason to doubt that. A few years ago, the enormously more respected folks at the OPERA experiment were willing to announce that they had seemingly detected neutrinos moving faster than light. Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community, and sure enough,…

>Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community

You make it sound like the scientists reporting it didn't doubt it.

Re: What we know about the EmDrive and Cannae Drive

#115

Post by api »

drzaiusapelord wrote: post #79
MCRed wrote: post #56

I've some direct experience with a similar situation. I can speak to the issue of "why hasn't spaceX or other major company experimented with this". During the "Cold Fusion" era, when Pons & Fleishman had claimed to develop room temperature fusion, I worked for a major US lab doing superconductor research. (We invented the first superconductors that operated at liquid nitrogen temperatures-- Y1B2C3O) While fusion isn…

This is one of the many reasons why I consider all "fururist" media as just sci-fi wish fulfillment for kiddies. Its just incredible how unreadable /r/futurology is, for example. Its just a lot of pats on the back about some amazing life-changing technology, that is eternally 10 years away. I don't have access to the Mondo 2000 stuff today, but if any of that was to believed we'd have AI masterminded rockets to moon…

The way I see it there are two sides to the hype coin: frothing believers and curmudgeonly skeptics. Both are simple minded and shallow. Both really come out of the woodwork for stuff like this.

BTW the reason SpaceX is more exciting than SLS is VTVL reusability.

Re: What we know about the EmDrive and Cannae Drive

#116

Post by api »

drzaiusapelord wrote: post #79
MCRed wrote: post #56

I've some direct experience with a similar situation. I can speak to the issue of "why hasn't spaceX or other major company experimented with this". During the "Cold Fusion" era, when Pons & Fleishman had claimed to develop room temperature fusion, I worked for a major US lab doing superconductor research. (We invented the first superconductors that operated at liquid nitrogen temperatures-- Y1B2C3O) While fusion isn…

This is one of the many reasons why I consider all "fururist" media as just sci-fi wish fulfillment for kiddies. Its just incredible how unreadable /r/futurology is, for example. Its just a lot of pats on the back about some amazing life-changing technology, that is eternally 10 years away. I don't have access to the Mondo 2000 stuff today, but if any of that was to believed we'd have AI masterminded rockets to moon…

The way I see it there are two sides to the hype coin: frothing believers and curmudgeonly skeptics. Both are simple minded and shallow. Both really come out of the woodwork for stuff like this.

BTW the reason SpaceX is more exciting than SLS is VTVL reusability.

Re: What we know about the EmDrive and Cannae Drive

#117

Post by kbenson »

pauloday wrote: post #82
drzaiusapelord wrote: post #79

Earlier quoted context omitted.

This is one of the many reasons why I consider all "fururist" media as just sci-fi wish fulfillment for kiddies. Its just incredible how unreadable /r/futurology is, for example. Its just a lot of pats on the back about some amazing life-changing technology, that is eternally 10 years away. I don't have access to the Mondo 2000 stuff today, but if any of that was to believed we'd have AI masterminded rockets to moon…

I love reading /r/futurology comments for comedy purposes, but I have a weird sense of humor

I just skip straight to /r/HFY. Might as well go to the source.

Re: What we know about the EmDrive and Cannae Drive

#118

Post by Dylan16807 »

Steuard wrote: post #78
Tossrock wrote: post #65

Earlier quoted context omitted.

Why isn't it worth getting excited about? I get excited about lunch. It costs me nothing to follow the progress on low-probability, high impact technological advancements (see: space elevators, commercial fusion power, etc)

I guess this is really the point: space elevators and commercial fusion are many, many orders of magnitude more likely to pan out than this is. Both of those are engineering challenges, and materials science challenges. They may be insurmountable ones, or they may not. But neither one would unconditionally require changes to the bedrock principles of physics. Human beings are not good at distinguishing between levels…

Well here's the thing. We could put a fully-functioning fast food restaurant on the moon by 2020. It's an engineering challenge and 100% surmountable. But we won't. It's more likely that we've fundamentally misunderstood physics than we would actually put in the effort to do that.

Re: What we know about the EmDrive and Cannae Drive

#119

Post by oldmanjay »

Bud wrote: post #111
Tossrock wrote: post #67

Earlier quoted context omitted.

It seems like an impossibly basic mistake, but confusing micro- and milli- newtons would make the math a lot more reasonable.

Not impossibly basic at all. Space missions have failed because of these kinds of basic math errors: http://www.wired.com/2010/11/1110mars-climate-observer-repor...

I almost want another failure so people will stop pulling this out as an all-purpose rhetorical showstopper.

Re: What we know about the EmDrive and Cannae Drive

#120

Post by gus_massa »

tonyhb wrote: post #105
Steuard wrote: post #17

Earlier quoted context omitted.

Yes, sure, they've measured something surprising. I have no reason to doubt that. A few years ago, the enormously more respected folks at the OPERA experiment were willing to announce that they had seemingly detected neutrinos moving faster than light. Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community, and sure enough,…

This doesn't have to violate conservation of momentum to work. We don't understand how it works yet, which precludes us from saying that it violates our current understanding of physics. I'm no physicist but this guy[1] is, and his paper — which is based off of research with evidence backing it up in the 1970's — suggests that the EmDrive creates propulsion from Unruh radiation[2]. [1] http://physicsfromtheedge.blogs…

If this is consistent with quantum mechanics, this must emit some kind of particles, the main candidates are photons (and far less probable gravitons, but some alternatives / variations claim to use gravity).

(I'm not sure about Unruh radiation, but the nice thing about radiation is that when you see it far enough, it doesn't depend on the details of the source, it's simple a bunch of photons. (Well, the color of the photon depends on the details of the source, but they are undistinguishable from other photons.))

If this is consistent with special relativity, and the particles are mass less, then the Force/Power ratio is at most 1/c, that is 0.0033 uN/W = 0.0033 mN/KW.

If the particles are not mass less, and you just create them at the moment to emit them, the ratio is even smaller, much smaller.

If the particles are not mass less, and just accelerate them from a reservoir, the ratio can be much bigger, but now you have a standard rocket, not a fuel-less rocket.

Someone compiled here a list of experiments, with the Force/Power ratio: http://forum.nasaspaceflight.com/index.php?topic=36313.msg13...

They vary from 3x to 200000x the theoretical maximum if we assume that this doesn't break the conservation of momentum, special relativity and quantum mechanics.

(Perhaps it's not necessary to use quantum mechanics, because the classical electromagnetic waves have the same Force/Power ratio, because they are actually a good approximation of the quantum electromagnetic waves. But the photons picture makes all clearer.)

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