EM Drive

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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Diogenes
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Post by Diogenes »

chrismb wrote:
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.

I don't know how closely anyone else has kept up with this, but years ago when I was looking at it I recall reading that Sawyers idea came from a practical problem they were having with satellite position keeping. Apparently he noticed that the satellites he managed were moving out of position and it appeared to be consistent with the direction of their microwave transmissions.

In other words, he claimed that real world experiments indicated a force of some sort which required propellant to offset.

That is supposedly what got him started on his "research."

Don't know if any of it is true, but if it is, real world experiment beats theory any day of the week.
‘What all the wise men promised has not happened, and what all the damned fools said would happen has come to pass.’
— Lord Melbourne —

kcdodd
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Post by kcdodd »

lol chrismb. Why not construe this as a ME drive. After all, the end plates are nothing but capacitor plates driven by resonant RF fields. So it could be pushing on the rest of universe too. Or transporting the momentum into the future. Or whatever it is the ME thruster is supposed to be doing to get around saying it doesn't conserve momentum.

@Diogenes The device being discussed here is not emitting any microwaves. It is just a resonant cavity with an asymmetric geometry. So even if it were true it wouldn't really matter. It would be like seeing a rocket engine work, and then attaching a rocket engine to the inside of a closed box and expecting the box to take off.
Carter

ladajo
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Post by ladajo »

Ahh, but his argument is that it is not really a closed box.

I wonder how open he has been with his test rigs? It would appear more so than Rossi. But, hard tellin, not knowin.

Diogenes
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Post by Diogenes »

kcdodd wrote:lol chrismb. Why not construe this as a ME drive. After all, the end plates are nothing but capacitor plates driven by resonant RF fields. So it could be pushing on the rest of universe too. Or transporting the momentum into the future. Or whatever it is the ME thruster is supposed to be doing to get around saying it doesn't conserve momentum.

@Diogenes The device being discussed here is not emitting any microwaves. It is just a resonant cavity with an asymmetric geometry. So even if it were true it wouldn't really matter. It would be like seeing a rocket engine work, and then attaching a rocket engine to the inside of a closed box and expecting the box to take off.
I'm aware of the design, i'm just relating to you what was claimed years ago when it first came out. The amount of deflection of the satellite was considered by Sawyer to be substantially in excess of it's equivalent light pressure.

From my understanding of his design, it looks like it should just heat a bunch of copper. :)
‘What all the wise men promised has not happened, and what all the damned fools said would happen has come to pass.’
— Lord Melbourne —

ladajo
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Post by ladajo »

I read through the 2010 paper, and it seems that they have gotten but in from a US aerospace company. He is also playing with a superconductor cavity.

I went through his paper again and saw no great leaps of logic.

http://www.emdrive.com/Toulouse2010paper01.doc

He also discusses in this paper where they tested it in a hermetically sealed container.

kcdodd
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Post by kcdodd »

The leap is to assume the waves can change momentum by going through the waveguide without interacting with the waveguide itself and exchanging momentum with it, thus canceling out the forces on the end plates. To show it does not violate momentum conservation one must account for all of the momentum such that total dp/dt = 0. Simply saying the system is open doesn't cut mustard. What is it interacting with? What is the momentum exchanged with? There are no holes!
Carter

ladajo
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Post by ladajo »

As I understood, the thrust "trick" lays within the two differing effective "group" velocities from either end of the wave guide. Which is a function of the smaller 'leading end' diameter and the slope of the chamber walls, from the larger end. He accounts for thrust energy this way, but also claims there is heating, and that is also a power loss. Which, as I took away, some argue may be creating a thermal thrust effect by heating air. Although, I am not so sure that can hold water if properly accounted in the vertical and inverted thrust tests, as well as the hermetically sealed box test, also with vertical and inverted thrust tests.

His data shows somethign is going on, and outside of the air heating principle, it woudl seem his chief detractors are only arguing that what he thinks is happening is not happening. Vice that anything is happening at all. In that, it is similar to the Mach Effect tests.

Edited for crappy spelling.

Nik
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Is this related to the 'closed funnel' widget ??

Post by Nik »

IIRC, that had normally staid theorists chewing the carpet...

Sadly, its proponents lack the $100k / kg required to flight-test it from the ISS's porch...

ladajo
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Post by ladajo »

Maybe the Airforce can flight test it with the X-37B. :)

GIThruster
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Post by GIThruster »

kcdodd wrote: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.
Carter, would you mind expanding on your reading of SRT here? Last week in another forum, a physicist made what I thought was a compelling argument that both thrust and acceleration are indeed velocity dependent. He didn't bring up SRT, but his argument seemed compelling and reduces to something like this:

In both the case of the chemical rocket, and an M-E powered craft, thrust and its consequent acceleration are functions of the exhaust velocity of the propellant (exhausted in the case of a rocket or recycled in the case of M-E) in the "lab", "launch" or "rest" frame. The faster the craft moves in this frame, the slower the propellant in relation to the frame, hence acceleration diminishes with time.

Now he didn't put it quite that way, but his point was that M-E powered craft ought not to be able to generate linear acceleration from linear power into the thruster, just as chemical rockets do not do this.

Did you have an argument from SRT that says this is wrong, that you can share on a popular level with guys like me, who are not physicists?

BTW I should share that I think Shawyer did make some horrendous math errors in the basic concept of his device. I haven't studied it in 2-3 years but it seemed to me your original take was exactly correct. Shawyer did not understand the concept of "group velocity" when he designed the thruster and it does involve impossible physics. This is why he's no longer getting official Brit funding. What's left of the project is probably just distraction--counter-intel. Just like the Baker stuff. . .

I think SRT is useful when looking at EM, but I think this other argument that force and acceleration are velocity dependent seems to apply to both chemical rockets and M-E thrusters.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

morganism
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Post by morganism »

Heard the Chinese test was a success, but havn't heard any details on what exactly that test was about.

We are planning on using microwave thrusters for our asteroid miners.
Those were a NASA design study, the Microwave Thermal Electric thrusters, with plain water as reaction mass. There is a new upgrade to those, ironically, with a resonant cavity !

chrismb
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Post by chrismb »

GIThruster wrote:Did you have an argument from SRT that says this is wrong, that you can share on a popular level with guys like me, who are not physicists?
Just regular Newtonian physics will do: The same force applied to a moving object for a given time does more work on that object than on a slower moving object over the same time. So if you generate a given amount of thrust, then the thrust does more work on a moving object the faster it goes in that frame.

GIThruster
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Post by GIThruster »

chrismb wrote:
GIThruster wrote:Did you have an argument from SRT that says this is wrong, that you can share on a popular level with guys like me, who are not physicists?
Just regular Newtonian physics will do: The same force applied to a moving object for a given time does more work on that object than on a slower moving object over the same time. So if you generate a given amount of thrust, then the thrust does more work on a moving object the faster it goes in that frame.
Chris, you've got the example backward. The point is that the higher the velocity of the rocket, the less force its thruster creates--so it's not a situation of "The same force applied. . ."
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

chrismb
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Post by chrismb »

GIThruster wrote:Chris, you've got the example backward. The point is that the higher the velocity of the rocket, the less force its thruster creates--so it's not a situation of "The same force applied. . ."
oh....dear...me....

So let me just get this right... someone drives by past where you are standing and they hold their arm out of the window and drop something. Does it stop instantaneously when it leaves the guy's hand?

Now, I will assume that you are not going to say 'yes' to that!!!

Now let's say that you didn't actually see the thing being dropped, but as you look up at it, you notice that it hits the floor very slowly but the car was going fast. Just tell me this - do you conclude that this thing got a big push backwards to slow it down enough that it didn't hit the ground fast, or do things really just slow down of their own accord, once thrown out of the car [air resistance notwithstanding]?

...and you are trying to tell US about ME effect!!!!... oh boy....

Aero
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Post by Aero »

I know better than to get involved, but I will anyway. GIT, have you considered that orbital velocity is 2 to 3 times the exhaust velocity of most rocket engines? (liquid bi-propellants) By your physicist's logic thrust would go to zero somewhere just about a third to half way to orbit, so I guess just like some believe that the moon landing was a hoax, the whole space program must be a hoax, too. Including communications and meteorological satellites.

The fact is, using rocket body centered coordinates, thrust is constant within engine tolerances. It is the thrust force on and the acceleration of the rocket body and its payload that rocket science is concerned with.
Aero

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