EM Drive

[MeDiCS]

http://blog.wired.com/defense/2008/09/chinese-buildin.html hmy:

A big IF...

 

[Master of Blades]

Sounds like bollocks to me...

 

[MeDiCS]

I think like that also, but IF...

 

[TSPenguin]

It sure would be great.
Let's just wait until one of our resident physicists explains to us why this can't work.

 

[RisingFury]

I think this goes against the rule of conservation of energy.

The guy who first proposed the idea said that because of relativistic effects, one side of the cone would be subjected to a slightly higher force then others.

But if that's so and you get a force acting on the body, then you're not losing any energy, but you can gain velocity... so, against the conservation of energy.


I think that if they built this and tested it and they got a slight force from it, it would probably be caused by the surrounding air that's being heated up and propelled against the shape of the object.

 

[Eagle]

One end of the resonant chamber is open (If I understand it correctly, but it seems a lot of the critiques act as if both ends of the frustum have end caps). So I would guess it might have thrust on the order of a flashlight (which does have some thrust).

Really the design reminds me of vortex tube.

 

[thomasantony]

Then should try and test it in space. Or at least, in a vacuum chamber. I read about this long ago on the wiki .. and even though my Physics mind kept rejecting it .. I wondered if its possible we missed something.

~
Thomas

 

[RocketMan_Len]

Until it gets off the drawing-board and into real-time use... it's just another Dean Drive to me...

 

[MeDiCS]

Dean Drive?

Well, the creator seems to think a bit 'off-center'. A plasma gun to shoot down satellites?

 

[Lunar_Lander]

Does that mean that we have a microwave radiation source and that one then produces thrust? That sounds like a crazy idea and I'd too say that this wouldn't work (OK, photons excert some thrust but only really little that it is almost unmeasurable).

 

[Belisarius]

From the article:

"It is well known that Roger Shawyer's 'electromagnetic relativity drive' violates the law of conservation of momentum, making it simply the latest in a long line of 'perpetuum mobiles' that have been proposed and disproved for centuries," wrote John Costella, an Australian physicist. "His analysis is rubbish and his 'drive' impossible."

Arthur C. Clarke's First Law (from Wiki)
"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."

Dr Costella doesn't seem that elderly, though. His debunking of the EM drive is pretty tough. "Pseudo-scientific hodge-podge", "complete rubbish" and "crackpot paper" are just some of the epithets that get thrown in.

 

[Urwumpe]

Luckily, it does not work.

Otherwise, any high-gain antenna operating at decent strength should produce noticeable thrust.

 

[cjp]

Luckily, it does not work.

Otherwise, any high-gain antenna operating at decent strength should produce noticeable thrust.

Not all antennas are the same. A normal dipole antenna emits cylindrically symmetric EM waves, so any thrust in one direction is exactly compensated by an equal thrust in the opposite direction.

An asymmetric emitter (like a satellite dish used for emitting EM waves) does produce thrust (as far as I can see now), but I think the magic word here is noticable. Even when a certain idea is physically possible, it can still be a long way to a usable engineering solution. In this case, I think the amount of electrical power per unit of thrust force is the important thing. It's probably way too large for any application.

 

[Urwumpe]

Not all antennas are the same. A normal dipole antenna emits cylindrically symmetric EM waves, so any thrust in one direction is exactly compensated by an equal thrust in the opposite direction.

An asymmetric emitter (like a satellite dish used for emitting EM waves) does produce thrust (as far as I can see now), but I think the magic word here is noticable. Even when a certain idea is physically possible, it can still be a long way to a usable engineering solution. In this case, I think the amount of electrical power per unit of thrust force is the important thing. It's probably way too large for any application.

Well, the key value in Newtonian physics is P = F * ve. As Einstein does not touch impulse this value should not be completely different and so, theoretical thrust should be similar to electrostatic thrusters. For producing one Newton of thrust, you would need at least 299.792458 MW electrical power (in reality even more).

 

[Eagle]

Well, the key value in Newtonian physics is P = F * ve. As Einstein does not touch impulse this value should not be completely different and so, theoretical thrust should be similar to electrostatic thrusters. For producing one Newton of thrust, you would need at least 299.792458 MW electrical power (in reality even more).

The momentum of the photon p is just the photon's total energy divided by the speed of light. p = e/c.

Checking our work, Google calculator says: 299.792458 MW / c = 1 N. So our math is correct.

Also changing the frequencies of our emission doesn't change our efficiency, only the number of photons we release. Releasing one photon at 299.792458 MW is the same thrust as releasing a google of photons (10^100) at ~3 x 10^-92 W. (Assuming floating point math didn't kill Google calculator.)


Of course this is Newtonian math, and this drive is based off of relativistic math anyways. Which I am extremely bad at.

 

[Urwumpe]

Of course this is Newtonian math, and this drive is based off of relativistic math anyways. Which I am extremely bad at.

No, why should it be really based on relativistic math?

I know that the guy writes that, but the debunk already found out: It does not need them. If the drive would accelerate propellants to nearly the speed of light, we would need Einstein to know the real exhaust velocity, but the impulse, the more critical value, remains the same.

 

[Eagle]

No, why should it be really based on relativistic math?

Well, just that Newtonian math lets our Orbiter craft exceed the speed of light, we (think we) know this isn't possible because of Special Relativity.

So, I think there is some value to doing relativistic math to debunk. Especially since that is what the author used.

 

[Urwumpe]

Well, just that Newtonian math lets our Orbiter craft exceed the speed of light, we (think we) know this isn't possible because of Special Relativity.

So, I think there is some value to doing relativistic math to debunk. Especially since that is what the author used.

We don't need relativistic math as long as we only observe just the spacecraft, and we don't need to look at more, for determining if a spacecraft produces thrust at all.

Relativistic math is needed to find out, where a spacecraft is going.