[JumpCrisscross]

Satellite orbits degrade overtime due to drag, among other things [1]. Operators counter this decay with periodic boosts. (The International Space Station is boosted, on average, once a month [2].) Boosting, even electric propulsion boosting, consumes propellant.

If this works by impelling against the Earth's magnetic field, provided it is more efficient than a simple magnet, it could still have a market with satellite manufacturers.

[1] https://en.wikipedia.org/wiki/Orbital_decay

[2] http://space.stackexchange.com/questions/9087/how-often-does...

[dom0]

> If this works by impelling against the Earth's magnetic field

That's a completely different premise than the em-drive has, though. It's supposed to not depend on an external field; developing a force between two magnets wouldn't exactly qualify as (non-)rocket science today.

[cjensen]

The "premise" for the em-drive has been determined to be a thorough misunderstanding of the physics involved, so you cannot rule out any potentially contributing force in the experiment.

Yes you heard that right: guys who misunderstand physics go and design a reactionless thruster which, when measured in their shoddy experimental setup, produces a measurable thrust.

If there really is a measurable thrust, then the Laws of Motion are wrong and General Relativity is wrong. I'm disinclined to believe that long-held principles of physics will be upended by some guys who designed something based on a misunderstanding.

[freehunter]

You sound very negative towards conducting more experiments on this, when the results have been unexpected every time it's been tested. You're displaying the kind of dogma that science has been fighting against since the dawn of time. Either it's true or it's not, but we can't tell until we test it. And so far, it's only been disproven in theory, not in practice. That's worth more experiments.

[cjensen]

Occam's Razor says it is not true. If you read the linked article, it is saying, in the most polite and disinterested way possible, that it is not true although they allow, in the driest of terms, that it could be true. I expect if the same authors analyzed the Loch Ness monster or Big Foot, they would also disinterestedly point out the unlikelihood of either and point out the how awful the proofs put forth are while admitting there is no categoric proof that the monsters don't exist.

Pons and Fleischmann were straightforward in their error. This is bozo territory.

[bicubic]

I don't expect the em-drive to work, but the parent post has a point. We've had repeated experiments yielding unexpected results. It's worth an inquiry; if nothing else, to thoroughly explain what went wrong so the same mistake is avoided in future experiments.

Outright dismissing new ideas, no matter how far-fetched, is very much the antithesis of the scientific principle. You mustn't forget that everything we take as indisputable fact today, was an outrageous far-fetched theory at some stage.

It was barely yesterday that Barry Marshall was ridiculed for proposing that stomach ulcers are bacterial, because everyone 'knew' that bacteria can't survive in such an environment.

[mhneu]

Many possibilities of what went wrong are well-explained in the parent article, drawing on experience of other scientists that make low-force measurements. (E.g. forces on rig due to electrical current flow, or liquid flow.)

Unfortunately it seems likely we won't learn much by finding the possible sources of error - the sources are already well understood by people doing low force experiments.

[euyyn]

> it's only been disproven in theory, not in practice

There's a hell of an experimental body that led to (and supports) our current laws of motion. These laws aren't "just theory", and they definitely aren't dogma. Are these experiments probing the laws in a region they haven't been tested before? Can these unexpected results be reproduced outside of the framework of a cool engine for space travel?

E.g. there's a difference between measuring for the first time the spectrum of antihydrogen, which we predicted with the strongest confidence would be the same as hydrogen's; and measuring the spectrum of hydrogen with Rock&Roll sounding within, because "we can't know if any specific music genre will have an effect until we test it".

So yeah, if people want to spend their own resources testing this, the more power to them. But the way it's been done makes it look like they're more interested in a cool positive result than in unveiling the truth, and that mindset leads to things like the N-rays.

[gus_massa]

> You sound very negative towards conducting more experiments on this, when the results have been unexpected every time it's been tested.

This is wrong. There is a strong selection bias, where a many team tried this and only those that got a "successful" measurement get press.

It's very difficult to get the list of all the unsuccessful (unpublished) experiments, but someone recollected a list em-drive test http://emdrive.wiki/Experimental_Results The important column is the last one. More than 1 means that if it's correct the device is breaking the current laws of physics. Anyway, I count 5 zeros in that list. [And I think that the other are experimental errors.]

[justinjlynn]

A relatively strong argument for experiment pre-registration as a prerequisite for eventually publishing.

[mhneu]

The only unexpected "results" happened in experiments with a lack of controls, so while nothing can be ruled out, it would not be surprising if all the data so far is explained by well known forces (like flow in the liquid supply lines.). It's on the previous experimenters to do proper controls.

[Bluestrike2]

But it's not dogma. Dogmatic principles are one "laid down by an authority as incontrovertibly true." 'Science'--with a capital 'S', denoting a specific authority--doesn't say that the laws of motion are accurate. Years of empirical research, with repeated and verifiable confirmations by other scientists, do. The laws of motion are held to be true not because scientific authorities say they are so, but because of the method by which they came to be able to say it.

It's a subtle distinction, but an incredibly important one. But that same subtlety can sometimes be lost when it's discussed by the general public. The policy debate over climate change is an excellent example. Speaking strictly in terms of the often quoted statement that "97 percent or more of actively publishing climate scientists agree," [0][1] it's clear how different individuals can read very different meanings into that statement. For the scientists themselves, while the statement is referring to scientists as individuals, it's based on the published research that informed their views. Amongst the general public, particularly those who don't accept anthropogenic climate change, the statement is understood as referring to the beliefs of the individuals. It's taken as an appeal to authority (and it doesn't help that many politicians and activists who want to take action often use it as such). The same statement is understood in two very different ways based on the reader's background and understanding of what the scientific method actually is.

Returning to the subject of the em-drive, the reason for skepticism is precisely because it flies in the face of our basic understanding of the physical world. The more well-founded a theory is, the greater the burden on any new findings that would seem to contradict it. That's as it should be. But if those new findings hold up under scrutiny and are verified, even a basic, fundamental law can and will be revised. That's how the scientific method works.

Personally, I'd love for the em-drive to be proven if only because it would represent such a fascinating shift in physics. To say nothing of potential applications. But I'm inherently skeptical. Not because of a dogmatic acceptance of the laws of motion, but because those laws are already so well-supported.

0. http://climate.nasa.gov/scientific-consensus/ 1. http://iopscience.iop.org/article/10.1088/1748-9326/11/4/048...

[stale2002]

The way science works is by doing experiments.

The people have been doing experiments on the EM drive and have been getting unexpected results.

Nobody really knows why yet, but that's kinda the point.

Is thermodynamics flawed? Is it pushing off of "dark matter"? Is it a completely new and novel scientific effect?

Any of these circumstances would be interesting.

[DanielBMarkham]

Yes. Even if it's the most likely thing, experimenter error, for a half-dozen teams to all have errors and not spot them? That's quite interesting! It's the same situation we had with the FTL neutrinos a while back.

[euyyn]

Except the neutrino paper then was a big lot of physicists asking colleagues to help them review, so as to find where the problem was. What I see here is just hype. The former, as opposed to the latter, is what gives confidence that the people involved are doing their darnest not to fool themselves. That what they're doing is actually science.

[DanielBMarkham]

I don't know. I see a few universities looking into building their own setup. I see the Chinese filing patents, testing them in orbit. I see a 2017 microsat launch. I see a healthy debate continuing over on the reddit Emdrive board.

That doesn't look like people trying to sell things to me. That looks like a lot of different people from different backgrounds playing around with an experimental setup that does something unexpected.

The only difference I see is that with the FTL neutrinos, folks were saying this breaks a mathematical model that we've proven over and over again. With the emdrive, folks are saying If this works, it's by some model we do not yet understand. It doesn't attempt to disqualify an existing model; it suggests there's some other model applicable that we don't quite understand yet.

For most folks, this is quite more upsetting than the FTL guys. I get that. Still, observe first, theorize second. I'm sure the theory folks will catch up, and it'll probably be some sort of EM leakage we're talking about. But maybe not. Maybe we've accidentally come up with a new kind of photon rocket. That's what makes the story fun.

[euyyn]

> It doesn't attempt to disqualify an existing model

It would very much disqualify conservation of momentum, which is another way of saying that the laws of motion are the same here and one meter down the road.

Conservation of momentum has been observed in countless experiments for centuries, in a broad range of conditions. It was indeed observed first; there's no catching up needed for the theory. It's always valuable, and in a sense exciting too, to test it again beyond the range where it's already been tested, even if you expect a negative result (the null hypothesis holding). But that's not what's happening:

If your goal is to learn, and you see momentum not being conserved in your prototype space engine, you start dismantling it, simplifying it, until you stop seeing it. And then go back one step to see it again. Your device might not be a space engine anymore! But now it's simplified; easier to reproduce, and easier to model and analyze. The laws of nature don't care about the purpose and coolness of your device, they apply the same. You also take your measurement apparatus and calibrate it against something unrelated, in many conditions, to make sure it's not lying.

You might have a different goal than learning: to achieve cheap space travel, which is a great thing. If then you build a prototype space engine with the hope that it won't conserve momentum, and you see a positive result, there's already the first red flag. If when you see that, what you do is trying to explain it with new (or with wrong) theory instead of questioning it, there's the second red flag. Healthy debates, and playing with technology in a lab, are good things. But not all good things are science. Our minds are too easy to fool, and people are doing this without condoms.

[mhneu]

> With the emdrive, folks are saying If this works, it's by some model we do not yet understand.

A summary of the parent article is "The experimenters did not do the obvious control experiments [e.g. testing under a null load], thus there are currently no results at all."

[matheweis]

But it would represent an improvement on what we have today, which is a finite amount of fuel use to keep the satellite in orbit that eventually runs out.

[sandworm101]

For the power required to generate minimal thrust, this will not be useful in low orbit. The solar panels required to power the drive would result in more drag than the truster might overcome. So no market. And this test flight will not result in a clearcut "it stays up" rather "it fell slower than expected". There will be much calculation and debate re drag, magnetics and gravitational anomolies, so small are the expected forces.

To get a clear result we need something out closer to geostationary, flying for months well away from the earth's irregularities.

[JumpCrisscross]

> For the power required to generate minimal thrust, this will not be useful in low orbit

A recent paper [1] quotes this system's predicted efficiency at 1.2 mN/kW. Hall thrusters, a propellant-throwing electric engine, perform at 60 mN/kW. Non-propellant systems like light sails, laser propulsion and photon rockets perform around 0.0033 to 0.0067 mN/kW.

If this works, and that's a big if, a 50x performance improvement over the prototype is not unrealistic.

[1] https://regmedia.co.uk/2016/11/09/q_thruster.pdf

[sandworm101]

But how big will the panels need be? And how much extra aerodynamic drag will they create in a low orbit?

[roywiggins]

Electrodynamic tethers push off the Earth's magnetic field directly and don't need fuel.