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#3000 by glennfish on 21 Feb, 2016 12:40
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I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror.
well, given that in a near perfect reflector pair you get F = 2NW/C where N is the number of bounces...
if the mirrors are physically attached so you get +F at one end and -F at the other, then if one is more efficient than the other, the imbalance would be something like 2NW/C <> 2(N-1)W/C or your net thrust would be F = W/C which is the simplest case of photon thrust. Your net imbalance would result in what you would expect without a mirror at one end, i.e. a classic photon rocket with no bounces.
See: https://en.wikipedia.org/wiki/Photonic_laser_thruster -
#3001 by MazonDel on 21 Feb, 2016 14:06
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Welcome back TheTraveller!
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#3002 by TheTraveller on 21 Feb, 2016 14:35
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Welcome back TheTraveller!
Thanks,
Well past my bedtime. Can't sleep. Will not be here (home) for long. More prostate cancer treatment (surgery and rad, maybe drugs) in the very near future. Hopefully the last.
All I can say is:
GET YOUR PROSTATE CHECKED! -
#3003 by Rodal on 21 Feb, 2016 14:40
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...I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror. Maybe by giving the photon some added mass when striking one mirror? (one mirror being a super-conductor possibly?). ...
No, this, by itself, still won't self-accelerate the center of mass, if it is a closed system.
As an analogy, think of an astronaut inside a spacecraft in space, throwing a ball towards an inner wall of the spacecraft.
At all times during this thought experiment, the astronaut, and the ball(s) are inside the spacecraft (since it is a closed system.)
If the collision of the ball against the wall is perfectly elastic, the ball comes back to the astronaut. The center of mass of the spacecraft does not self accelerate.
If the collision of the ball against the wall is perfectly plastic, such that the ball gets stuck onto the wall and it does not comes back to the astronaut, the center of mass of the spacecraft still does not self accelerate.
The astronaut can keep throwing thousands of balls against the wall that stick to the wall and don't bounce back (due to perfectly plastic collision), and still the center of mass of the spacecraft still does not self accelerate.
All you are achieving by this action is to change the position of the center of mass of the spacecraft with respect to intrinsic body-fixed coordinates, just as if you would be moving the furniture to one corner of the spacecraft. The center of mass of the spacecraft will not experience self-acceleration due to these internal actions. -
#3004 by TheTraveller on 21 Feb, 2016 14:54
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As an analogy, think of an astronaut inside a spacecraft, throwing a ball towards an inner wall of the spacecraft.
And this example is related to EM waves propagating from small end plate to big end plate and back to small end inside a resonant EmDrive with a tapered waveguide how?
Or are you declaring that the momentum transfer from the big and small end plate radiation pressure is the same at each end of the EmDrive?
Not a challenge. Just desire to understand how you see it. -
#3005 by Rodal on 21 Feb, 2016 14:55
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I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror.
well, given that in a near perfect reflector pair you get F = 2NW/C where N is the number of bounces...
if the mirrors are physically attached so you get +F at one end and -F at the other, then if one is more efficient than the other, the imbalance would be something like 2NW/C <> 2(N-1)W/C or your net thrust would be F = W/C which is the simplest case of photon thrust. Your net imbalance would result in what you would expect without a mirror at one end, i.e. a classic photon rocket with no bounces.
See: https://en.wikipedia.org/wiki/Photonic_laser_thruster
No, you don't achieve any self-acceleration of the center of mass of the closed system that contains both mirrors. The center of mass of the closed system that envelopes both mirrors does not self accelerate. The center of mass of the system that envelopes both mirrors does not experience any force. All you are doing is to re-distribute the location of the center of mass-energy of the system with respect to the mirrors, the center of mass-energy will not self-accelerate or experience a force.
Take a look at the photonic laser thruster papers.
The center of mass of the closed system that contains both the mission vehicle and the resource vehicle does not self-accelerate.
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#3006 by Rodal on 21 Feb, 2016 15:04
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It is obvious that it was dustinthewind the one that raised this example:As an analogy, think of an astronaut inside a spacecraft, throwing a ball towards an inner wall of the spacecraft.
And this example is related to EM waves propagating from small end plate to big end plate and back to small end inside a resonant EmDrive with a tapered waveguide how?
......I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror. Maybe by giving the photon some added mass when striking one mirror? (one mirror being a super-conductor possibly?). ...
My understanding is that dustinthewind raised this example as an independent thought experiment. You can address your question of any possible analogy to the EM Drive to dustinthewind, as to whether he intended any such analogy. I certainly did not interpret dustinthewind as claiming that there was any such analogy, as you appear to infer. -
#3007 by TheTraveller on 21 Feb, 2016 15:13
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It is obvious that it was dustinthewind the one that raised this example:As an analogy, think of an astronaut inside a spacecraft, throwing a ball towards an inner wall of the spacecraft.
And this example is related to EM waves propagating from small end plate to big end plate and back to small end inside a resonant EmDrive with a tapered waveguide how?
......I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror. Maybe by giving the photon some added mass when striking one mirror? (one mirror being a super-conductor possibly?). ...
My understanding is that dustinthewind raised this example as an independent thought experiment. You can address your question of any possible analogy to the EM Drive to dustinthewind, as to whether he intended any such analogy. I certainly did not interpret dustinthewind as claiming that there was any such analogy, as you appear to infer.
With respect Dr. Rodal, I asked you your opinion on my question about differential radiation pressure (momentum transfer) on the small & big ends of an EmDrive.
I'm not being confrontational or aggressive at all. I would like to know your opinion. -
#3008 by Monomorphic on 21 Feb, 2016 15:15
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Interesting that in the paper & attachment:
http://www.deepspace.ucsb.edu/wp-content/uploads/2015/11/Brashears-etal-SPIE-2015-Interstellar-WaferSats-v07b-comments-removed.pdf
If I read this correctly, they propose using ~100 gigawatt lasers to accelerate a ~70 gram wafer spacecraft with a ~1 meter sail to ~ 0.25c in ~10 minutes.
Fortunately, Robert Forward calculated what it takes to scale this kind of system up to carry humans when he wrote Rocheworld ~30 years ago:
"The light used in the system was an array of a thousand laser generators, which were focused through lenses and aimed at the sail. The lasers provided up to 1,500 terawatts of power. Two different lenses were used to magnify the laser beams. The acceleration lens was 100 km in diameter and was able to accelerate the ship at 0.01g; the deceleration lens was 300 km in diameter and was able to decelerate the ship at 0.1g. Although these accelerations are relatively small, over time they result in enormous speeds.
To catch the energy, Forward used a 1,000-km-diameter, circular aluminum sail. The sail resembled a flattened disk with a 300-km diameter removable center portion. When traveling to Rocheworld, the entire sail was used. When the ship needed to decelerate, the smaller sail was separated from the larger outer sail. The large sail was used as a reflecting lens, focusing light onto the smaller sail, slowing the craft.
Using the light sail system, the spaceship Prometheus continued to accelerate for 20 years, traveling 2 light years' distance toward Barnard's Star before going into coast mode and traveling an additional 20 years' time at a constant speed of 0.2 c, covering the remaining 4 light years (ca. 23 trillion miles; 38 trillion km)." -
#3009 by TheTraveller on 21 Feb, 2016 15:20
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Interesting that in the paper & attachment:
http://www.deepspace.ucsb.edu/wp-content/uploads/2015/11/Brashears-etal-SPIE-2015-Interstellar-WaferSats-v07b-comments-removed.pdf
If I read this correctly, they propose using ~100 gigawatt lasers to accelerate a ~70 gram wafer spacecraft with a ~1 meter sail to ~ 0.25c in ~10 minutes.
More papers at the full site here, including a road map:
http://www.deepspace.ucsb.edu/projects/directed-energy-interstellar-precursors -
#3010 by craigel on 21 Feb, 2016 15:23
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I hope I'm not being dense, but this simplicity of this analogy is too tempting for me. It seems like if the astronaut was outside of the spacecraft, then the ball and the astronaut would both move in opposite directions right? If so, it seems like the same thing would apply if the astronaut was inside (and attached to the craft somehow), only now it is the astronaut+spacecraft and the ball. So wouldn't the spacecraft move ever so slightly in one direction before the ball hits the far wall and forces it backwards?...I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror. Maybe by giving the photon some added mass when striking one mirror? (one mirror being a super-conductor possibly?). ...
No, this, by itself, still won't self-accelerate the center of mass, if it is a closed system.
As an analogy, think of an astronaut inside a spacecraft in space, throwing a ball towards an inner wall of the spacecraft.
At all times during this thought experiment, the astronaut, and the ball(s) are inside the spacecraft (since it is a closed system.)
If the collision of the ball against the wall is perfectly elastic, the ball comes back to the astronaut. The center of mass of the spacecraft does not self accelerate.
If the collision of the ball against the wall is perfectly plastic, such that the ball gets stuck onto the wall and it does not comes back to the astronaut, the center of mass of the spacecraft still does not self accelerate.
The astronaut can keep throwing thousands of balls against the wall that stick to the wall and don't bounce back (due to perfectly plastic collision), and still the center of mass of the spacecraft still does not self accelerate.
All you are achieving by this action is to change the position of the center of mass of the spacecraft with respect to intrinsic body-fixed coordinates, just as if you would be moving the furniture to one corner of the spacecraft. The center of mass of the spacecraft will not experience self-acceleration due to these internal actions. -
#3011 by TheTraveller on 21 Feb, 2016 15:36
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I hope I'm not being dense, but this simplicity of this analogy is too tempting for me. It seems like if the astronaut was outside of the spacecraft, then the ball and the astronaut would both move in opposite directions right? If so, it seems like the same thing would apply if the astronaut was inside (and attached to the craft somehow), only now it is the astronaut+spacecraft and the ball. So wouldn't the spacecraft move ever so slightly in one direction before the ball hits the far wall and forces it backwards?...I wonder if it is possible to have a single device (closed system) that has two mirrors but one mirror is more effective at harnessing energy from the photon than the other mirror. Maybe by giving the photon some added mass when striking one mirror? (one mirror being a super-conductor possibly?). ...
No, this, by itself, still won't self-accelerate the center of mass, if it is a closed system.
As an analogy, think of an astronaut inside a spacecraft in space, throwing a ball towards an inner wall of the spacecraft.
At all times during this thought experiment, the astronaut, and the ball(s) are inside the spacecraft (since it is a closed system.)
If the collision of the ball against the wall is perfectly elastic, the ball comes back to the astronaut. The center of mass of the spacecraft does not self accelerate.
If the collision of the ball against the wall is perfectly plastic, such that the ball gets stuck onto the wall and it does not comes back to the astronaut, the center of mass of the spacecraft still does not self accelerate.
The astronaut can keep throwing thousands of balls against the wall that stick to the wall and don't bounce back (due to perfectly plastic collision), and still the center of mass of the spacecraft still does not self accelerate.
All you are achieving by this action is to change the position of the center of mass of the spacecraft with respect to intrinsic body-fixed coordinates, just as if you would be moving the furniture to one corner of the spacecraft. The center of mass of the spacecraft will not experience self-acceleration due to these internal actions.
Inside an EmDrive, the ball, being the resonant EM wave, delivers less momentum transfer at the small diameter end than at the large diameter end due to the guide wavelength being longer at the small end than the big end. As Cullen showed in 1951, end plate momentum transfer (2 x radiation pressure) is less inside a circular waveguide than outside the waveguide and the reduced end plate momentum transfer is related to the standard radiation pressure equation X (external wavelength / internal waveguide guide wavelength), plus guide wavelength, inside a waveguide, increases as diameter reduces.
This variation in radiation pressure / momentum transfer between the small and big end plates, driven by guide wavelength variation, driven by diamater change, is purely speculative as I have no direct proof, other than Cullens 1951 experimental data and my measured ~8mN of reaction force generation at ~90W of forward Rf power into my badly constructed, hand made, low Q frustum.
A higher quality, fully molded & machined frustum is in the works that I expect to see at least 20mN of reaction force being generated and maybe between 30 and 40mN of reaction force being generated.
So the perfectly elastic ball example is not a valid thought experiment. -
#3012 by Rodal on 21 Feb, 2016 16:02
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..I hope I'm not being dense, but this simplicity of this analogy is too tempting for me. It seems like if the astronaut was outside of the spacecraft, then the ball and the astronaut would both move in opposite directions right? If so, it seems like the same thing would apply if the astronaut was inside (and attached to the craft somehow), only now it is the astronaut+spacecraft and the ball. So wouldn't the spacecraft move ever so slightly in one direction before the ball hits the far wall and forces it backwards?
No, the center of mass of the spacecraft does not self-accelerate when an astronaut inside it throws a ball, even before the ball contacts the walls. All that happens is that the position of the center of mass shifts ever so slightly with respect to the intrinsic geometry of the spacecraft, just as if the astronaut would slide the furniture inside the spacecraft, or re-arrange the position of any objects within the spacecraft. Such an action will shift the position of the center of mass with respect to the intrinsic geometry,but it does not at all self-accelerate the center of mass of the spacecraft.
Also, if the astronaut is floating in outer space by herself, and throws a ball into space, the center of mass of the astronaut-ball system never self-accelerates. All that happens is that the astronaut moves in the opposite direction to the direction of the ball.
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#3013 by SeeShells on 21 Feb, 2016 16:04
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For electromagnetic radiation, where T is the Maxwell stress tensor, is the force density, S is the Poynting vector, c is the speed of light, and is the momentum density.
*Attached image
CoM is one of the most researched, powerful and fundamental laws about nature we have. I'm having a hard time wrapping my mind around it being violated, even with asymmetrical differential stresses the mass and energy will in total time be conserved. Maybe some are seeing something that I can't.
Even in the Alcubierre Warp Drive it stretches spacetime in a compression type wavefront and it still doesn't violate CoM.
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#3014 by TheTraveller on 21 Feb, 2016 16:11
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For electromagnetic radiation, where T is the Maxwell stress tensor, is the force density, S is the Poynting vector, c is the speed of light, and is the momentum density.
*Attached image
CoM is one of the most researched, powerful and fundamental laws about nature we have. I'm having a hard time wrapping my mind around it being violated, even with asymmetrical differential stresses the mass and energy will in total time be conserved. Maybe some are seeing something that I can't.
Even in the Alcubierre Warp Drive it stretches spacetime in a compression type wavefront and it still doesn't violate CoM.
Shell,
The EmDrive is a differential radiation pressure momentum transfer engine. Same as the constant radiation pressure, constant Force photonic thruster is a momentum transfer engine.
As spacecraft Velocity increases due constant Force & Energy from A = F / M, so too does spacecraft Momentum increase as M * V. -
#3015 by Rodal on 21 Feb, 2016 16:26
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There appears to be some confusion in these pages with people that have forgotten Rocket Propulsion and conservation of momentum.
Again, the photonic thruster's center of mass (for both the mission vehicle and the resource vehicle) never, ever, self-accelerates. As the mission vehicle moves forward, the resource vehicle must move backwards.
See:
http://www.ux1.eiu.edu/~cfadd/1350/09Mom/Rock.html
http://www.physicsclassroom.com/class/momentum/Lesson-2/Momentum-Conservation-in-Explosions
http://www.braeunig.us/space/propuls.htm
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#3016 by TheTraveller on 21 Feb, 2016 16:29
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There appears to be some confusion in these pages with people not familiar with Rocket Propulsion 1.00 and conservation of momentum.
See:
http://www.ux1.eiu.edu/~cfadd/1350/09Mom/Rock.html
http://www.braeunig.us/space/propuls.htm
Dr. Rodal,
Will you please answer my question?:
http://forum.nasaspaceflight.com/index.php?topic=39004.msg1494061#msg1494061
And the above post is relevant to a propellantless EmDrive that throws nothing out the tail pipe to accelerate how? -
#3017 by SeeShells on 21 Feb, 2016 17:02
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For electromagnetic radiation, where T is the Maxwell stress tensor, is the force density, S is the Poynting vector, c is the speed of light, and is the momentum density.
*Attached image
CoM is one of the most researched, powerful and fundamental laws about nature we have. I'm having a hard time wrapping my mind around it being violated, even with asymmetrical differential stresses the mass and energy will in total time be conserved. Maybe some are seeing something that I can't.
Even in the Alcubierre Warp Drive it stretches spacetime in a compression type wavefront and it still doesn't violate CoM.
Shell,
The EmDrive is a differential radiation pressure momentum transfer engine. Same as the constant radiation pressure, constant Force photonic thruster is a momentum transfer engine.
As spacecraft Velocity increases due constant Force & Energy from A = F / M, so too does spacecraft Momentum increase as M * V.
You ever wonder why someone couldn't punch their way out of a closed paper bag? If I'm not making the bag react to outside forces, floor, walls, ceilings, air, no mater how you impact you create on the sides of the bag, no matter the time it takes for the energy you impact the side of the bag in any form of mass or energy or even virtual particles it HAS TO get out to react to the outside world. IF I suck up and make Virtual Particles from the Quantum Vacuum and if they don't get out they will just increase the local energy inside of the bag.
You must take the force or energy you create in the bag to the outside world to get it to move. I've stated almost since day one give me a hole and I'll give you thrust from the drive. Our universe's first laws were entropy and the conservation of mass and energy even when it was just a mix of Quarks and Gluons and the fundamental forces hadn't even expressed themselves. The only thing that seemed to find a backdoor to violating that basic fundamental of CoM or CoE was spacetime which to me acts like a huge entangled Zero Point Energy force that can work with spooky actions outside the laws of causality.
On another note:
I am feeling much better and feel I've got my MoJo back.
Yesterday I tore apart a spare Panasonic magnetron and removed the heat fins to replace them with a water cooling jacket of copper wound tubing. Still need a little more work on it but here are the first results.
Shell
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#3018 by Rodal on 21 Feb, 2016 17:11
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There appears to be some confusion in these pages with people not familiar with Rocket Propulsion 1.00 and conservation of momentum.
See:
http://www.ux1.eiu.edu/~cfadd/1350/09Mom/Rock.html
http://www.braeunig.us/space/propuls.htm
Dr. Rodal,
Will you please answer my question?:
http://forum.nasaspaceflight.com/index.php?topic=39004.msg1494061#msg1494061
And the above post is relevant to a propellantless EmDrive that throws nothing out the tail pipe to accelerate how?
The only way that I am aware of that a closed system could self-accelerate its center of mass and respect conservation of momentum-energy is if its initial total mass-energy was zero (for example as a result of containing equal amounts of negative mass-energy as positive mass-energy).
Otherwise the rest mass of the system must be variable with time and there has to be creation of negative mass-energy.
See
http://forum.nasaspaceflight.com/index.php?topic=39214.msg1487251#msg1487251 and the following posts.
A much simpler solution is to consider the EM Drive as an open system, for which there are many coherent proposals.
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#3019 by dustinthewind on 21 Feb, 2016 17:11
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Imagine then the analogy of a ball created out of one wall, inside the ship,
since photon propulsion is propellant-less.Now imagine this ball is perfectly elastic and has an initial velocity. We are going to do a trick we modify the mass of the ball when it strikes one of the walls such that the energy exchange to the walls is more efficient. When the ball strikes the other wall it is back to its previous mass where the energy exchange is less efficient. Eventually the ball will slow down because its energy is being given to the structure as a whole.
The ball is in analogy to a photon so instead of slowing down it is red-shifted.
I attached a gif of the math I did below. It shows the % of energy exchanged between a wall and the ball depends on the mass of the ball. You then have to consider independently the exchange between two different walls where the mass of the ball is modified with each bounce. This is the reason I suggested the super-conductor because I think it suggested it could modify the mass of the photon. (One wall being a superconductor.) The idea is supposed to conserve momentum.
The ball will of course change velocity with each bounce but we then sub the new velocity in and figure the exchange of energy when it bounces again. Eventually most the energy is given to one wall rather than the other.
Maybe, it's possible this idea could be related to the Woodward thread.
Yesterday I tore apart a spare Panasonic magnetron and removed the heat fins to replace them with a water cooling jacket of copper wound tubing. Still need a little more work on it but here are the first results.