Quote from: WarpTech on 06/13/2015 08:25 pmThe two are not equal, because the wave decays in the time longer time t + dt, before it can transfer its momentum to the other side.In the most extreme case, where the photon is completely absorbed, all its momentum is transferred to the endplate on the first contact. But even in this case, the momentum applied to the endplate will be equal and opposite to the momentum applied to the power source when the photon was generated, so there would be no net thrust. The most efficient way to achieve thrust from photon momentum is to remove the resonator entirely and simply emit the photons away from the spacecraft in a coherent beam.
The two are not equal, because the wave decays in the time longer time t + dt, before it can transfer its momentum to the other side.
Wait a minute, I missed something… and I can't find it searching the thread. Where did we obtain Yang's frustum dimensions from? A few pages ago we complained she didn't published them.
Quote from: SeeShells on 06/13/2015 02:29 pm... you seem to violate CoM but don't let that be a brick wall just because someone tells you it does ...As it relates to the EmDrive I've put Conservation of momentum on a shelf for later examination. Candidly, I have quietly wondered if it might have a loophole or two for someone who was clever enough to find them. I seriously doubt I'm that clever.Playing in that vein, I have a related thought experiment.Imagine the space shuttle in orbit. The cargo bay doors are open. An astronaut equipped with an MMU fires his gas jets, accelerates from space outside the shuttle, and smacks into the back wall of the cargo bay. The astronaut transfers his momentum to the shuttle, and recieves a concussion for his trouble.The momentum flow is Gas from the Jets go left, shuttle goes right. CoM is satisfied.Two asprin later the astronaut+mmu is in the cargo bay with the bay doors closed and sealed. The bay is a hard vacuum. The astronaut reluctantly fires the MMU jets and smacks into the back wall again. A small amount of momentum is transferred to the shuttle, and the astronaut rethinks his "glamorous" career with Nasa.For conservation of momentum to be satisfied the force of the gas striking the inside of the cargo bay must exactly balance the force of the shuttle to the right for there to be no net momentum change. This exact balance of gas pressure does not match my understanding of gas behavior at all. I expect instead to see the all kinds of non-Newtonian action in the gas as it expands randomly into the bay in all directions. Turbulence and brownian motion will rob energy out of the gas literally left and right.I also don't see what would prevent the astronaut from pulling out a vacuum pump and compressing it back into the MMU's cylinders for another shot.I have an idea about how to test this here on earth, but the EmDrive work seems much more urgent and promising.Could someone point out the obvious flaw in my thought experiment? Despite having it drawn on my bathroom mirror since October, I've still not managed to see it.
... you seem to violate CoM but don't let that be a brick wall just because someone tells you it does ...
I had the same idea! If the astronaut were smart, he would close the bay doors and put his back up against the wall before firing his MMU. The shuttle would start moving instantly, before the gas could reach the other side. When it finally reaches the other side, turbulence and heat will have dissipated much of it's energy and nothing needs to leave the shuttle. I can't imagine why it would not work.
Quote from: aero on 06/14/2015 01:56 am...Three dimensions flux1: 2.25E+000 7.13E-009 -4.8601123862force1: 2.25E+000 -3.46E-008 Two dimensions flux1: 2.25E+000 2.24E-010 -4.4050439326force1: 2.25E+000 -9.85E-010 Check the file names to determine what was a 2D run and what is a slice of a 3D run. Note the files ending in 02.png show the antenna location. That is, 2 time steps after startQuote from: deltaMass on 06/14/2015 01:58 amSo what's the big picture wrap up of 2D vs 3D?the distribution of the electromagnetic field inside and outside look very differentand the calculated values look quite different tooWhich way is the force ? is it pointing towards the small end forward? or is the opposite way?
...Three dimensions flux1: 2.25E+000 7.13E-009 -4.8601123862force1: 2.25E+000 -3.46E-008 Two dimensions flux1: 2.25E+000 2.24E-010 -4.4050439326force1: 2.25E+000 -9.85E-010 Check the file names to determine what was a 2D run and what is a slice of a 3D run. Note the files ending in 02.png show the antenna location. That is, 2 time steps after start
So what's the big picture wrap up of 2D vs 3D?
Could someone point out the obvious flaw in my thought experiment? Despite having it drawn on my bathroom mirror since October, I've still not managed to see it.
Quote from: ElizabethGreene on 06/13/2015 11:07 pmCould someone point out the obvious flaw in my thought experiment? Despite having it drawn on my bathroom mirror since October, I've still not managed to see it.I think that as soon as the container (shuttle) starts to move, it creates a slight pressure gradient within the container which creates forces that oppose that motion, even in a situation with a rarefied gas. It might take a long time for everything to go back to "zero", but it eventually would. That's my prediction, anyway.
I think that as soon as the container (shuttle) starts to move, it creates a slight pressure gradient within the container which creates forces that oppose that motion, even in a situation with a rarefied gas. It might take a long time for everything to go back to "zero", but it eventually would. That's my prediction, anyway.
Data from second Baby EmDrive testhttps://hackaday.io/project/5596-em-drive/log/19468-torsion-test-2-data
Ok...it be way past time for one of the DIY types here to take a shot at duplicating the Yeng / Fan EM Drive design.