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[wierd]

"Don't believe the EMDrive claims made by the media, they suck and add sensationalist spin to everything. The creator of this device has followed a pattern of behavior that closely mirrors snakeoil salesmen, and should raise red flags. The research done on the EMDrive that is actually rigorous is not terribly voluminous-- in fact, there is very little at all. There have been published documents detailing small thrusts generated however, which warrants actual investigation-- but that investigation has not been conducted to a degree (that the author finds acceptable) that definitively states that the EMDrive works, and that the reported thrust is not experimental error. The media has conflated the findings of a fringe project group (eagleworks) working inside NASA for findings made by NASA. "


Basically.

However, this falls into several anthropic biases-- 1) Our research is better than theirs. (A chineese research lab initially did tests, which were discounted--- because?) 2) We know how to physics damnit, this does not work! (And whatever measurements you get MUST be experimental error!)  3) It looks like something, so it is! (The inventor's behavior follows patterns of historic snake oil salesmen, so he must be selling snake oil)

As a consequence, I would caution the author against commiting crimes of hubris.  Experiment is the ONLY valid thing to take to this table. He is right to point out that there is little experiment-- but why is that? These devices are NOT that complicated; they are just modified microwave ovens. A garage tinkerer could build one. What basic reason is there to NOT test this thing? Oh--- yeah, reputation of the researcher. That's right. It's a toxic thing, because it's snake oil (and it is snake oil because it hasn't been tested!)  Nice and self-referrential there.

Just build and test the damn thing if you want to refute it, stop hiding behind circular reasoning and logical fallacies.

[Karlito]

BTW, there seems to be something amiss in that article:

While the current maximum reported efficiency is close to only 1 Newton/kW (Prof. Yang’s experiments in China), Mr. March noted that such an increase in efficiency is most likely achievable within the next 50 years provided that current EM Drive propulsion conjectures are close to accurate.

In 2008, Wired magazine reported that a team of Chinese researchers led by Juan Yang (杨涓), professor of propulsion theory and engineering of aeronautics and astronautics at Northwestern Polytechnical University (NWPU) in Xi'an, claimed to have developed a valid electro-magnetic theory behind the Emdrive.[3][26] A demonstration version of the drive was built and tested under different cavity shapes and at higher power levels in 2010.[10] A maximum thrust of 720 mN was reported at 2,500 W of input power on an aerospace engine test stand usually used to precisely test spacecraft engines like ion drives.[7][11][12][13][27]

"mN" refers to millinewtons, right? Is there a slight disparity here?

It's only off by a factor of 3.5. 1 N/kW is basically a first order approximation.

[wierd]

720mM / 2.5kW == 288mN /1kW

That's a factor of someplace in the ballpark of 3.4 from the reported 1N/kW.

The way I choose to interpret it, is that the data was noisy, and that the "Highest reported peak" was in the 1N/kW range, while the adjusted data normalized to 288mN/kW.

[andrea]

and beside, considering that they still haven't got a solid idea of the cause of that thrust, the number of things that can cause such a relatively small difference is limitless.

From what I gather,  this EMdrive is worthy of cautios optimism. experiments from unrelated sources claim that there is some anomalous thrust, which is promising. Can't wait for proper, more definitive tests. Sure worth investigating, especially since, as it was pointed out, it is basically a modified microwave.

[wierd]

Re-reading the quoted bits--

The initial experiments with a 1st gen prototype produced the 720mN/2.5kW value.
Subsequent tests with revised prototypes have yeilded thrusts up to 1N/kW, according to researchers in China.
The chinese researcher states that he believes significant increases in efficiency will be gained through additional research over the next 50 years. (Hey, I need funding monies! Give me funding monies, and I strongly suspect we can turn this into something cool!)

[LordBucket]

So apparently there are articles floating around saying that NASA did test the emdrive in vacuum and it apparently really does work :v

One of those articles is from nasaspaceflight, and contains a highly detailed (if really succint) explanation on how it does not break the law of conservation of momentum.

...I read that a little while back and tracked down the source. It turned out to be a forum post from one of the scientists actually working on the project. He was saying....if  I understood correctly, that they attempted a vacuum test, but when the results cam back it turned out that their test chamber had failed, and that it was leaking air. Not so much that a human would notice, but enough that they couldn't reasonably claim that they did a proper vacuum test. From context, it sounded like the equipment was going to need to be replaced,


So yes, they did a vacuum test, and yes the results were positive. But because of the leak the quality of the test wasn't sufficient for him to go out and say that yes they did a vacuum test.

The articles citing him neglected to mention that detail.

I'll see if I can track down the original statements.

[PyroDesu]

Just a comment, but...

If the EM Drive actually works, I will personally be terrified. It seems distressingly easy to make and doesn't require propellant, only energy (on the physics front, perhaps instead of violating Newton's laws, it's simply an efficient photon drive? Photons can act as reaction mass (with the best possible exhaust velocities, hands down), it's just really, really, really, really inefficient).

An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT.

Think about that for a moment. Now add in a device that allows you to generate significant (relatively) amounts of thrust with only energy input. This could easily add up to a whole new class of WMD. Imagine, if you will, that a country with the ability to put things in orbit puts up something with this drive and solar panels (or possibly a smallish fission reactor) to power it, all massing... 7150 kilos (about the mass of a Soyuz craft), for the sake of argument. They then put it in an orbit eccentric enough that it will impact a target at about 11km/s. That would be equal (approximately) to a 26.5 kiloton bomb. Little Boy, the nuclear device dropped over Hiroshima, had a yield of about 15 kilotons. This is assuming they don't just put it out to the edge of Earth's sphere of influence and fall in under power. Or swing around Mars or Jupiter and back, again under power.

Am I saying that it should never be allowed to exist? No. But I bet it would be under very, very tight control, or at least, there would be an attempt to keep it under control, or to limit the possibility of someone attempting to use it as an easy kinetic weapon (Orbital branch of the military, anyone?).

[TheDarkStar]

Can't we already make kinetic impactors with conventional rockets?

[PyroDesu]

Can't we already make kinetic impactors with conventional rockets?

Not very easily. Seriously, it's easier to make a nuclear device, Tsiolkovsky's Equation is a bitch. You need reaction mass to carry the payload, reaction mass to carry the reaction mass to carry the payload, reaction mass to carry the reaction mass to carry the reaction mass to carry the payload, so on and so forth.

[wierd]

Can't we already make kinetic impactors with conventional rockets?

Not very easily. Seriously, it's easier to make a nuclear device, Tsiolkovsky's Equation is a bitch. You need reaction mass to carry the payload, reaction mass to carry the reaction mass to carry the payload, reaction mass to carry the reaction mass to carry the reaction mass to carry the payload, so on and so forth.

If you want to consider "OMG, The sky is falling!", you are thinking too small.

Instead, imagine this:

We send a vehicle up that is basically just a big fission reactor, some landing gear, a guidance computer, and a shitload of these engines.  We soft-land it on a large metallic asteroid. We activate the engines, and we move the asteroid out of orbit, and into a collision course with the earth.  It may take a very long time to get it here, but it would eventually get here assuming sufficient energy reserves were sent with the thrusterpack.

To do this with conventional engines, we would need to spend literally hundreds of billions of dollars just on orbiting all the propellent needed to send to the asteroid. This makes it a non-starter as far as major world governments considering it as a showstopper WMD.  However, with a genuine massless drive, and the absurd energy density of proper nuclear reactors (NOT little RTGs like is on Curiosity), It now becomes feasible to create such a plan, launch the vehicle, and then park the kinetic impactor at one the legrange points until the big red button is pushed.

Superfun times to be had by all on that day.

To me, though, the bigger curiosity is the laser interferometry data reported in their informal forum discussion linked earlier. The michaelson-moorley experiment famously showed that there is no cosmic aether, and specifically, that there is no aetheral wind. It looked for anomalies in interfermetric measurements from a split light beam, measured in multiple directions, while undergoing movement.  It is famous for showing that even when moving, there is no deviation in the local speed of light.  The interferometry data reported shows local deviation in the local speed of light when the device is active. That's where the alcubierre warp drive rhetoric is coming from.  This indicates a pretty profound finding in and of itself. Screw propulsion, this is a very exciting thing if true.

[PyroDesu]

Can't we already make kinetic impactors with conventional rockets?

Not very easily. Seriously, it's easier to make a nuclear device, Tsiolkovsky's Equation is a bitch. You need reaction mass to carry the payload, reaction mass to carry the reaction mass to carry the payload, reaction mass to carry the reaction mass to carry the reaction mass to carry the payload, so on and so forth.

If you want to consider "OMG, The sky is falling!", you are thinking too small.

Instead, imagine this:

We send a vehicle up that is basically just a big fission reactor, some landing gear, a guidance computer, and a shitload of these engines.  We soft-land it on a large metallic asteroid. We activate the engines, and we move the asteroid out of orbit, and into a collision course with the earth.  It may take a very long time to get it here, but it would eventually get here assuming sufficient energy reserves were sent with the thrusterpack.

To do this with conventional engines, we would need to spend literally hundreds of billions of dollars just on orbiting all the propellent needed to send to the asteroid. This makes it a non-starter as far as major world governments considering it as a showstopper WMD.  However, with a genuine massless drive, and the absurd energy density of proper nuclear reactors (NOT little RTGs like is on Curiosity), It now becomes feasible to create such a plan, launch the vehicle, and then park the kinetic impactor at one the legrange points until the big red button is pushed.

Superfun times to be had by all on that day.

This is true, but my description was more intended as a, this is going to open up the possibility of kinetic impactor WMDs to the wider global community, than we could totally recreate the Chixulub impact event.

And again, if it does turn out to be real (keeping a large reserve of skepticism here), then it's wonderful, but I expect it to have quite a few eyes kept on it because of the potential.

[i2amroy]

Yeah, kinetic energy is OP, but the fact is that in most cases it is too OP, conquering a place for it's resources isn't much use when you've annihilated any of the resources that were there in the first place. The fact is that the vast majority of conflicts come down to either "I want what he has" or "we both want this", which makes you having the ability to destroy both your enemy and the thing you were fighting over kinda irrelevant; since you still don't get the thing you want. This would basically just turn out to be a more cheaper atom bomb that trades time-costs to remove the upper limit on it's detonation area.

And the "what if a crazy dictator gets access to it?" argument? I'd like to point out that so far every crazy dictator that has gained access to nuclear weaponry has quickly becoming very sane. Truth of the matter is that having a bomb to blow up other people isn't that useful when you are guaranteed to be blown up yourself, and promises of great rewards to be found in heaven after death are much less appealing when you are currently enjoying great rewards here on Earth. Society and religion have done a great job at creating things that appeal to people with the power to change things but not kill us all, while not really appealing to those who actually can kill everyone and everything.

[Eagleon]

How do you aim a relativistic weapon with this kind of acceleration? It seems shaky to use it that way, and it'd be impossible to use it in a timely manner. Nukes or biological weapons would probably be easier for an intrepid Dr. Doom to acquire. 87% c (kinetic energy at half rest mass equivalence) is on the order of 6000 times the escape velocity from the sun.

[i2amroy]

How do you aim a relativistic weapon with this kind of acceleration? It seems shaky to use it that way, and it'd be impossible to use it in a timely manner. Nukes or biological weapons would probably be easier for an intrepid Dr. Doom to acquire. 87% c (kinetic energy at half rest mass equivalence) is on the order of 6000 times the escape velocity from the sun.

With a huge amount of math/computer programming before hand, combined with an acceleration system that can automatically make course corrections without human intervention (which we already are doing with our modern space and missile programs anyways). For example if I was the US and I was scared Russia might bomb me, I would figure out an algorithm that automatically calculated the trajectory to the Russian capital from wherever the weapon's current location was. Then once I gave the go signal the weapon would constantly be taking in trajectory location data and using it to adjust the course. It's just basic rocket science.

But yeah, this isn't a "we need a strike now" type of weapon. As I mentioned, it trades the strike speed for the ability to not have any real limits on it's upper destruction power, and the fact that it's basically unstoppable; at those speeds even were you somehow able to detect the incoming object it would be fairly worthless to destroy it, and in fact a fair number of designs actually include destroying themselves to maximize the area of destruction. In fact even assuming you somehow managed to detect the tiny rock traveling at speeds such that you would only detect it minutes before it actually hit your only real defense would be to hit it with something going sideways fast enough to make it miss, a thing that would require accelerations orders of magnitude faster than whatever was used to hit you. The fact of the matter is that if your enemies decide to take long enough to accelerate an object with the maximum delta-V technology available, it's becomes literally impossible for you to dodge because there is no way for you to produce the delta-V needed in another object to make it miss.

[Eagleon]

Have they ruled out thermal pitting yet on the surface of the larger section? Just heat forming microscopic spalls from overstressed metal crystals that are ejected like rocket fuel? This is probably completely the wrong place to ask, but I saw heat diagrams where the bigger half was getting much hotter on their forums and I'm a little concerned.