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EM Drive

Posted: Fri Mar 04, 2011 1:56 am
by ladajo
So, if we hook this up to a 2 million volt DC Battery, how long would it take to reach .5 Light?

Posted: Fri Mar 04, 2011 5:35 am
by Ivy Matt
Less than twelve parsecs. :wink:

Posted: Fri Mar 04, 2011 9:56 am
by Skytreker
Amazing! Isn't propellantless engine like the holly grail of space flight?! :shock: Especially like for long duration interstellar flights for which a conventional drive would require astronomical quantity of propellant.

The notion towards such form of propulsion I've encountered so far was that it is impossible because of violation of Newtons laws for conservation of momentum. I guess none has considered an EM wave to act as propelling force. (well except for solar sails but here the EM energy is produced on-board) So implications must be huge for space travel!

Posted: Fri Mar 04, 2011 11:21 am
by chrismb
Yes. It is indeed impossible. I've mentioned this chap before here. He has a piece of kit pluged into the wall. Same issue I have raised with "Mach effect" thrusters applies - the reaction force causing the motion is likely being borne by the electrons pushing back on the generator generating the electical power.

You need an electrical supply that is in the same inertial frame as the motive parts, to exclude this [simple] interpretation.

Posted: Fri Mar 04, 2011 2:18 pm
by Professor Science
Yet another potentially super disruptive technology that made a splash while i was in high school that nothing has happened with in the intervening half decade. I was rather excited about it then too, played around with a colony ship built around the idea of a poly-well and EMdrive travel combo.

Posted: Fri Mar 04, 2011 2:35 pm
by ladajo
So they argue that it is similar to solar sail and also:
A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.
and elsewhere, talking about the use of superconducting magnetrons:
It is worth noting that a problem identified during the development of these symmetric cavities is the detuning caused by mechanical deformation due to internal EM radiation pressure!

I dunno. He thinks he gots something, and it looks like they have support and funding to beon the way to a flight test:

Either way, I think he is building his case well enough. There is certainly enough theory and description on the website to chew on. I personally would like to see it tested with on board pwer in a vacuum chamber. But, we shall see in any event.

I do not buy Chris's argument. Plenty of test articles producing some type of thrust have been powered from off platform.

Posted: Fri Mar 04, 2011 2:50 pm
by Diogenes
I've been watching this closely ever since New Scientist published their article on "the End of Wings and Wheels" or some such.

Anyone seen his test video? Looks interesting, but As Chrismb says, it ought to be a relatively simple thing to power the whole contraption off of batteries, and therefore eliminate one potential source of a false positive.

The fact that the man has not already done so and posted a new video is evidence against him in my mind. At the moment, I classify the whole enterprise as a farce/fraud, but I am willing to look again if something new is demonstrated.

Posted: Fri Mar 04, 2011 3:06 pm
by kcdodd
Propellantless drive is not the same as reactionless drive. The second implies violation of conservation of momentum and is impossible in understood physics. This engine is an example of this type because it never exchanges momentum with the outside universe.

A propellantless drive, however, just uses something other then matter to exchange momentum. There is then no violation of momentum. It is entirely possible to use EM waves to expel momentum to create a propellant less drive. However, the reason noone does it is because of E = p*c for EM radiation (E = energy, p = momentum, c = speed of light). Or taking the time derivative P = F*c (P = power, F = force). Just plug in the numbers. To get one Newton of force requires 3*10^8 (300MW) of power. The space shuttle main engine is like 2 MN, which means an EM drive equivalent would require 600TW of power.

Posted: Fri Mar 04, 2011 3:17 pm
by ladajo
What did you make of his numbers in his theory section, and especially when compared to his posted test data?

He seems to be tracking per his predictions.

Posted: Fri Mar 04, 2011 4:11 pm
by chrismb
ladajo wrote:He seems to be tracking per his predictions.
... which also includes [reading between the lines] that there must be an 'absolute zero' velocity in the universe. Sawyer has already made the claim that it works 'more efficiently' the faster it goes - I did ask him whether he got more thrust at night or in the day (an extra >1000kph eastwardly!!!). That way we would be able to figure out which way it is towards the 'truly stationary' point in the Universe!!!

All these inertial fantasies ultimately boil down to inferring that there is a truly stationary point within the (our, 3D) Universe. This is nonsense within the framework of knowledge that is regarded as science, today. And I am sure it will always be so.

His experimental set-up is so fraught with complications - the round-the-bend electrons and the fluid and heating/air-cooling motions - that it is not anything near what I would consider a controlled experiment of scientific merit.

Posted: Fri Mar 04, 2011 4:21 pm
by Tom Ligon
I must have been in junior high school, maybe even earlier, when I first heard about ion propulsion, and wondered what it would take to rig up a science fair demo. Even at that early age, and with a propulsion system who's dainty thrust should overwhelm most pure EM approaches (flashlight thrust), I realized the difficulty in measuring the thrust meaningfully. Any net magnetic field produced from the current flow would play havoc with the net force.

Basically, I'll believe it when I see it move itself in space. I would be very hard to convince with any terrestrial amateur setup.

That said, it looks like a fun hobby, and I've done things with 9V batteries that would make you cringe. At 2.45 GHz and 850 W, he's using microwave oven parts ... as we did at EMC2.

There have been some speculations regarding the completeness of Maxwell's equations, specifically a possibly missing term of disputed importance originated by Grassman via Lorentz, which supposedly predicts a net force generated by certain antenna configurations. If the missing term is valid, and if I follow the arguments right, Special Relativity becomes invariant rather than covariant, and no net thrust occurs. I have no strong feelings on this, but got sucked into a few minor tests by one of the proponents. Anyway, the device may have some use for testing the issue.

Posted: Fri Mar 04, 2011 4:43 pm
by kcdodd
Could you be more specific about what numbers? In regards to his theory, it just seems confused at several basic levels.

He begins by deriving a net thrust by saying the photons have different momenta at each plate and thus exert different thrust as they reflect. However, he ignores the fact that the photons in his theory change momentum without interacting with anything! This is exactly where his theory violates conservation of momentum. They just magically change momentum while traveling between the plates. Where did the momentum go? I could make a guess.

He then derives an equation giving the thrust as a function of velocity of the engine. So, he either ignores, or doesn't know, that in special relativity the thrust should not transform in this way. In the direction of travel T' = T (for T = thrust in the rest frame of the engine), no matter how fast the engine is going.

So, assuming he derived any numbers form his theory I would not expect them to predict anything physical.

Posted: Fri Mar 04, 2011 4:52 pm
by Skipjack
But the mach thruster does not break the conservation of momentum! Just like a wheel pushes against the ground, the mach thruster pushes against the rest of the universe.
I dont quite see the problem with that. It still needs energy in order to accelerate from what I understand. So it does not violate the conservation of energy either.
The EM- drive is- from what I understand- a very different matter.

Posted: Fri Mar 04, 2011 5:00 pm
by chrismb
Skipjack wrote:But the mach thruster does not break the conservation of momentum! Just like a wheel pushes against the ground, the mach thruster pushes against the rest of the universe.
I dont quite see the problem with that. It still needs energy in order to accelerate from what I understand. So it does not violate the conservation of energy either.
The EM- drive is- from what I understand- a very different matter.
This could be equally claimed for the EM drive.

It is, merely, a claim that ME drive doesn't break conservation of momentum. It sure as heck looks like it does to me.

An EM drive is just an ME drive going backwards.

Posted: Fri Mar 04, 2011 5:06 pm
by Skipjack
It sure as heck looks like it does to me.
How? If you push against the rest of the universe, you are effectively not breaking conservation of momentum. Of course that would only work if Woodwards theory about the origins of inertia are correct.
If they are not, the whole thing falls apart.

I have heard lots of bad things about the EM- drive and it seems to be very different from the MLT. So why you are comparing them, I dont quite understand.
Anyway, it seems that there is some more development going on in regards to the EM, which is strange, because it should be completely discarded by now. I guess some things just take a long time to die.