Reactionless Space Drive

[slgrieb]

OK, I'm stretching a point here, but this article describing recent tests of an engine that appears to violate the law of Conservation of Momentum is interesting.

That's not to say that there aren't multiple issues with the test and theories about how this engine actually generates any thrust at all. The tests were conducted in a sealed compartment, but it wasn't evacuated, so we could just be seeing an incredibly inefficient version of the ionic wind effect that makes these lifters fly.

The Chinese supposedly conducted similar tests in 2012 with higher power levels and got higher thrust figures, but, once again, the important details are missing. Just thought it might be fun to toss it out for discussion.

[CeeBee]

OK, I'm stretching a point here, but this article describing recent tests of an engine that appears to violate the law of Conservation of Momentum is interesting.[/URL]fly.

How is it violating?
A device emits photons which have an impulse and in return we see thrust.

[slgrieb]

How is it violating?
A device emits photons which have an impulse and in return we see thrust.

The kicker here is that the Cannae drive, like the earlier EmDrive, is a closed chamber. http://en.wikipedia.org/wiki/EmDrive So, it isn't functioning anything like a conventional rocket, ion drive, etc. Unless this is an ion wind effect, something decidedly weird is going on.

Back in the day when those little ionic lifters were pretty new, some speculated that they worked by creating some sort of antigravity effect. But, it's been proven that isn't the case. Heck, even Mythbusters did a segment on them, and one of the first things they did was pop them in a test chamber and evacuate it. The result was that the lifters wouldn't lift off.

So, I'd have to say that to date, all the tests of this technology appear to be seriously sloppy and flawed. Who knows what the Chinese are doing. I think the biggest obstacle to evaluating these engines is the fact that everybody "knows" they can't work. Just like before Galileo, everyone "knew" that heavier objects fell faster than lighter ones. Still, I just can't believe that 5 guys from NASA ran this test without using an evacuated chamber.

The NASA test used one engine based on Cannae's reference design, and another (which according to Cannae's design theory shouldn't have produced thrust) and found them both to have identical performance. So, the one thing clear at this point, is that nobody understands the physics behind how the drive works. The mechanism may turn out to be prosaic or exotic, but we just don't know. I find that intriguing and exhilarating.

[CeeBee]

Given that the solar sail is a proven thing, I fail to see why reflecting more photons at one end than at the other wouldn't basically create a larger solar sail dragging a smaller one.
We are talking about photons, not about moving "matter".
And also Mythbusters.. hmmm in 99% of instances they fail to replicate something and call it "busted". SHowbiz with a touch of science.

[slgrieb]

Given that the solar sail is a proven thing, I fail to see why reflecting more photons at one end than at the other wouldn't basically create a larger solar sail dragging a smaller one.
We are talking about photons, not about moving "matter".
And also Mythbusters.. hmmm in 99% of instances they fail to replicate something and call it "busted". SHowbiz with a touch of science.

A solar sail uses light from an exterior source impacting on the sail to generate thrust. There is nothing odd about the physics here. There have been some theoretical studies done on using ground based, or orbital lasers to add some push to solar sails, and even some research into using honking huge lasers as a photonic drive. If you read any old SF, you can find these concepts in old Niven and Pournelle SF. The Mote in God's Eye is perhaps the best known of these stories, but one of Niven's earliest short stories describes an encounter between aliens (Kzinti) and a human starship using photonic propulsion.

But enough with the SF BS and reminiscing about old times. Both the Cannae and EmDrive seem to generate thrust without shooting anything out of the ass end of the drive. So, regardless of how the resonating chamber is shaped, since it is completely closed, the net thrust of bouncing a bunch of microwaves around inside the chamber should be zero. Once more, just to be clear, since you clearly fail to grasp the concept, the Cannae engine isn't squirting microwaves out it's ass to generate thrust. This all happens in a sealed chamber. So, with no photons leaving the building, how is any thrust developed? I'd say either ion wind or weirdness.

Regarding your comments on Myth Busters, in this case it isn't germane to the discussion. I cited a simple test that they did to disprove lifters flying by antigravity, and any general remarks you make about the show aren't relevant. it never ceases to amaze me how you can be so technically competent, yet such a stupid SOB at the same time.

[CeeBee]

Once more, just to be clear, since you clearly fail to grasp the concept, the Cannae engine isn't squirting microwaves out it's ass to generate thrust. This all happens in a sealed chamber. So, with no photons leaving the building, how is any thrust developed?

No, I grasp the concept very well and it puzzles me why it's so difficult to understand. Maybe because photons aren't your typical Newtonian mechanics "projectiles" and the chamber is not like your conventional thrust engine.
I'll give you something to think about: put a bulb inside a sealed reflective cylinder and paint one end black. Wouldn't you expect a net force? The photons would get absorbed by the black end but reflected by the mirror end resulting in a net force. Different pressure forces and no, it's not like in a cylinder filled with gas where the forces exerted by the pressure would absolutely be equal.

[slgrieb]

No, I grasp the concept very well and it puzzles me why it's so difficult to understand. Maybe because photons aren't your typical Newtonian mechanics "projectiles" and the chamber is not like your conventional thrust engine.
I'll give you something to think about: put a bulb inside a sealed reflective cylinder and paint one end black. Wouldn't you expect a net force? The photons would get absorbed by the black end but reflected by the mirror end resulting in a net force. Different pressure forces and no, it's not like in a cylinder filled with gas where the forces exerted by the pressure would absolutely be equal.

Whatever thrust you develop in a closed system doesn't translate into external thrust. So you can have a sealed bottle with your light bulb and dark target, and it can't move the system at all. Holy shit! Did you flunk Physics 101? Sorry, but the law of Conservation of Momentum says that you don't get thrust without pushing against something. In conventional propulsion systems like a rocket engine, shoving super hot gas out of the rocket nozzle creates thrust by pushing back against the engine. You can't get external thrust without throwing something away. Whether it's a rocket engine, a jet engine, or just the recoil from a fire arm. Perhaps this is a better explanation than I can give you.

So, that's the core issue with the Cannae Drive and the EmDrive. They are closed systems that generate external thrust without shoving anything out of the ass end of the drive. That shouldn't work. Apparently, though, it does. So, that is why most scientists dismiss the drive out of hand. It can't work so it doesn't. Experimental evidence to the contrary not withstanding. So, again, I think that leaves us looking at ionic wind effects, or weirdness. Because the thrust is so low, I'm inclined toward weirdness, as in an unknown effect of physics, as the likely answer.

[CeeBee]

You push "against" the fucking photons. And unlike a fucking steel ball, a fucking photon may stop to exist. It has no fucking rest mass but it has a fucking impulse. What the fuck is so hard to comprehend?

[Gazzak]

If you put 2 CeeBee's in a sealed box would they argue?

[Larommi]

If you put 2 CeeBee's in a sealed box would they argue?

There are two of them?

Is the other one a physicist too?