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#3300 by dustinthewind on 22 Jun, 2016 22:58
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In regard to the underlined comment.I have been contemplating if it is thermal energy that is the source of propulsion. Our universe seems to be on the increase in entropy and along with that our universe is expanding. One wonders if the two are not related. The thought was that one end of the drive is more hot than the other? I thought it was but not sure how that compares to the total surface area. Thermal energy radiated forwards compared to that radiated backwards. If memory serves me correct NASA got more of a thrust when putting the dielectric top which made the top more cool? Or do I have it backwards and it is the top that was more hot?
1) Yes,, thermal energy in the form of thermal convection has been a source of experimental artifacts ever since Maxwell first conceived thermal radiation pressure. Thermal radiation pressure was not experimentally confirmed until the year 1900 in which Russian physicist Pyotr Lebedev came out with the ingenious idea of... carrying out an experiment in a vacuum chamber.
The idea being that the light is losing energy to creation of thermal currents. This would not quite be a reflection and allows the radiation to travel through the cavity. The idea being that there is an unequal sharing of photon energy (thermally) in the cavity after many bounces which allows more efficient harnessing of photon energy. Where normally the energy lost after 1 reflection is equivalent to the Doppler shift of a reflected photon. The cavity having many reflections, and non-symmetric induction in the cavity (evidenced by unequal thermal distribution - if there is any) allows Doppler-shifting the light to thermal wavelengths in a non-symmetric manner
Could this be what they were talking about when they were suggesting light is escaping the cavity. In a thermal sense? Such that technically, it's not a reflection?
2) Yes, it is notorious that the inventor of the EM Drive, Roger Shawyer has never reported a single experiment conducted in a vacuum chamber, given the well known history of thermal radiation pressure experiments and such experimental artifacts. Particularly since he has been working on his invention for decades.
3) It is also notorious that those that conducted EM Drive experiments in a vacuum chamber (NASA and TU Dresden) reported much smaller anomalous force/InputPower when performing the experiments in a vacuum chamber than under ambient conditions.
4) Asymmetric thermal (black body) radiation takes place by emitting photons, (as opposed to thermal convection that takes place by fluid motion of air molecules in the atmosphere) and hence it can never result in propulsion exceeding the force/PowerInput of a perfectly collimated photon rocket: 1/c.
Hence claims of anomalous force/InputPower in excess of 1/c cannot possibly be explained as being the result of asymmetric thermal radiation (asymmetric thermal radiation as for example being responsible for what used to be known as the "Pioneer anomaly" until it was satisfactorily explained by JPL's analysis).
But yes, they certainly can be explained as resulting from spurious experimental artifacts due to convection of air molecules by fluid/thermal transport from the hotter surface in experiments not performed in vacuum chambers.
Otherwise, how can thermal dissipation result in self-acceleration exceeding by orders of magnitude the one of a perfectly collimated photon rocket?
The only known way I know how to get some amazing form of thrust out of light is a recycled photon rocket or possibly in a cavity, via some phenomena that causes the photon to give up a different ratio of energy with respect to one side of a cavity as opposed to the other. Without this a photon just loses energy to the cavity and then re-gains it when hitting the other side. If there were evidence that photons were giving more energy to one side than the other it could cause self acceleration. the photons would eventually lose energy and the cavity would gain that energy.
Normally an impact of a photon gives up very little energy but by recycling photons this depletion of energy is increased as seen with a photon recycling rocket which gives thrust much greater than a photon rocket. Now a recycling photon rocket is not like a closed cavity, (different concepts), but if a photon can be induced to give up more energy to one side of a cavity then they both (recycle photon rocket and cavity) can drain the energy from photons more efficiently than a single reflection off of a solar sail. The big question is if we can cause this non-symmetric distribution of photon energy in a cavity.
I was looking down the road of uneven thermal energy distribution by the reflected photons as a possibility. -
#3301 by FattyLumpkin on 23 Jun, 2016 03:52
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dustinthewind, would you please provide links or references to "recycling photon rockets". I believe this is what I had in mind re my resonant EM rocket concept (although I was unable to explain in a cogent fashion that which was going on in the noggin).
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#3302 by dustinthewind on 23 Jun, 2016 05:31
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dustinthewind, would you please provide links or references to "recycling photon rockets". I believe this is what I had in mind re my resonant EM rocket concept (although I was unable to explain in a cogent fashion that which was going on in the noggin).
Its not the same as the cavity, as the two parts are separate (mirror and laser). The light bounces many times between. However with each bounce a small amount of energy is transfered to the mirror. Normally this energy transfered from the photon to the mirror is extremely small, but with many bounces a larger amount of energy can be transfered.
https://en.wikipedia.org/wiki/Photonic_laser_thruster
If the effective mass of the photon changes, then the % of energy exchanged between the photon and the cavity also changes, which is why I was looking into the photon mass changing in the cavity such that it was heavier on the narrow end of the cavity. I was thinking of it as a sort of Woodward effect. There may be some problems with this concept. How the mass would change may cancel out any benefits. It is just a thought. Some papers do suggest light may have mass but it is normally thought not to have mass. Other papers were looking into the thermal aspects and it got me thinking out loud.
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#3303 by FattyLumpkin on 23 Jun, 2016 07:06
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So light waves/photons are shorter than micro waves.(attachment) and this cannot be done with microwaves and E M microwave mirrors because? It would be a pulsed system as the micro waves would build up and then be "released" creating a pulse of force?
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#3304 by dustinthewind on 23 Jun, 2016 07:27
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So light waves/photons are shorter than micro waves.(attachment) and this cannot be done with microwaves and E M microwave mirrors because? It would be a pulsed system as the micro waves would build up and then be "released" creating a pulse of force?
All light seems to provide impulses in the form of photons.
A recycled photon rocket can be with with any wavelength, I think, 1/2 the distance of the mirrors, or smaller. The concept is just that the light has to bounce many time between two mirrors "that are not attached to each other" <-important point because the cavities mirrors are attached to each other. The light between the mirrors of a photonic recycling thruster is amplified with a gain medium. The light provides a pressure.
To cause the frustum cavity to resonate at a particular mode requires radiation of a particular wavelength and shape. There is also consideration of cutoff wavelengths where the dimensions of the frustum approach the minimum length that radiation is allowed to occupy. Simulations are run to predict a cavities behavior to an antenna that injects radiation. The cavity is not expected to develop thrust, (the mystery of the EM drive), but the photonic recycling thruster is expected to behave as it does. I wasn't sure what you wanted to know exactly so I might have said too much. -
#3305 by RERT on 23 Jun, 2016 11:21
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http://scitation.aip.org/content/aip/journal/adva/6/6/10.1063/1.4953807
On the exhaust of electromagnetic drive by Patrick Grahn1,a), Arto Annila2,3,b) and Erkki Kolehmainen4,c)
"Our claim that the EM drive expels paired photons in the same way as a heat engine exhausts thermal photons entails that the vacuum, as the ultimate dump, comprises of photons"
There have been a few references here to this paper. I personally couldn't follow their logic as to why thrust is greater than a photon rocket, in particular their equation 4. However, I found it quite interesting that this is a variant of the many-threads-ago comment: that the exhaust is distorted spacetime. They take this argument a speculative step forward by making it more concrete, namely they speculate that the vacuum is populated by pairs of oppositely polarised photons, and that the em drive essentially expels momentum-containing pairs of photons - i.e. vacuum. Where I can't connect the dots is that if the photons maintain their momentum in an oppositely polarised pair, they presumably also retain their energy, and hence the efficiency is at best 1/c. If anyone can explain that I'd be interested to listen.
Still, I find the idea of a 'wake' of modified spacetime/vacuum as one of the least-bad possibilities for explaining the EM drive, giving it an invisible exhaust.
R. -
#3306 by Monomorphic on 23 Jun, 2016 12:58
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I found this symposium talk by Lubin to be pretty enlightening with respect to the photonic laser thruster. The whole video is great, but I particularly enjoyed the question and answer portion beginning at 18:00
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#3307 by Mulletron on 23 Jun, 2016 14:50
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Probably the most informative thing I've learned in a while. The magnetic vector potential. I wasn't taught about this. Looks like it's effect on charged particles extends beyond where the B field is contained. A bit of the history about it and why it shouldn't have been left out. Might be neat to see what happens if someone does a double slit experiment with a resonator between the slits. Also I don't remember it being discussed here.
https://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect#Magnetic_solenoid_effect
The Feynman paper discusses whether the magnetic vector potential is "real" vice just a mathematical construct also does quite a lot of myth busting at the end.
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#3308 by Mulletron on 23 Jun, 2016 16:06
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Well all this research about the nonintuitive aspects of closed loops, strange behavior of shorted coils on YouTube and vector potentials lead me to a strange coincidence. I knew I had read something before similar to the abstract about constrained and unconstrained motion. I just found this and haven't had time to digest it yet.
http://iopscience.iop.org/article/10.1088/1367-2630/14/9/093020
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#3309 by Rodal on 23 Jun, 2016 18:07
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Well all this research about the nonintuitive aspects of closed loops, strange behavior of shorted coils on YouTube and vector potentials lead me to a strange coincidence. I knew I had read something before similar to the abstract about constrained and unconstrained motion. I just found this and haven't had time to digest it yet.
This paper reflects the confusion that I see in the literature concerning all these "paradoxes" including the Abraham-Minkowski paradox and the Feynman paradox. This paper starts by defining the force as being only due to the divergence of the stress tensor. It ignores the contribution from the time derivative of the Poynting vector. Then, it writes:
http://iopscience.iop.org/article/10.1088/1367-2630/14/9/093020QuoteThe approach taken by Vaidman [17] as applied to the A–C system is one in which internal
motion of the system manifest itself in ‘hidden momentum’ that affects the motion of the
neutron. The time derivative of this ‘hidden momentum’ or the hidden force, as one may refer
to it, is applied directly to the equation of motion
as you see this "hidden momentum" is only "hidden" from those like the authors that do not take into account ALL terms in the conservation of momentum equation. The so called "hidden momentum" is the momentum due to the time derivative of the Poynting vector, that the authors neglected to take into account in the first place.
As remarked in the classic monograph "Electrodynamics of moving media" by Prof. Penfield and Haus at MIT in the 1960's confusion will ensue if authors neglect to take into account ALL terms in the equations of motion. Another source of confusion is that the ONLY force that has a physical meaning is the force that can be measured in an experiment, which is the total force. The forces due to the divergence of the stress tensor and the time derivative of the Poynting vector cannot be measured experimentally in general. Also, such decompositions of forces are not unique (which is another source of confusion in so-called paradoxes because authors often ignore that there is an infinite number of ways that one can define momentum and decompose momentum into separate components as well as decompose forces into separate components). Again what matters is to take into account from the beginning, ALL terms in the conservation of momentum equation and to define as "force" a force that can be measured experimentally.
Those interested in a discussion of this subject, as it pertains to the EM Drive, including the errors made by authors calculating forces for the EM Drive purely based on using Maxwell's or Yang-Mills equations, see:
http://forum.nasaspaceflight.com/index.php?topic=39214.msg1546438#msg1546438 -
#3310 by Rodal on 23 Jun, 2016 18:53
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Could you explain how is this proposal different from McCulloch's ?dustinthewind, would you please provide links or references to "recycling photon rockets". I believe this is what I had in mind re my resonant EM rocket concept (although I was unable to explain in a cogent fashion that which was going on in the noggin).
Its not the same as the cavity, as the two parts are separate (mirror and laser). The light bounces many times between. However with each bounce a small amount of energy is transfered to the mirror. Normally this energy transfered from the photon to the mirror is extremely small, but with many bounces a larger amount of energy can be transfered.
https://en.wikipedia.org/wiki/Photonic_laser_thruster
If the effective mass of the photon changes, then the % of energy exchanged between the photon and the cavity also changes, which is why I was looking into the photon mass changing in the cavity such that it was heavier on the narrow end of the cavity. I was thinking of it as a sort of Woodward effect. There may be some problems with this concept. How the mass would change may cancel out any benefits. It is just a thought. Some papers do suggest light may have mass but it is normally thought not to have mass. Other papers were looking into the thermal aspects and it got me thinking out loud.
Thanks -
#3311 by FattyLumpkin on 23 Jun, 2016 20:01
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dustinthewind, I was not suggesting the two mirrors were connected. If one were to perform the same experiment with microwaves (without a propagating medium) would there be a "build up" of so much/many particles/waves as to produce thrust? Please see attached
One can or cannot image these as microwaves?
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#3312 by Rodal on 23 Jun, 2016 20:11
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dustinthewind, I was not suggesting the two mirrors were connected. If one were to perform the same experiment with microwaves (without a propagating medium) would there be a "build up" of so much/many particles/waves as to produce thrust?
This was addressed before as TT was proposing to run EM Drive experiments without side walls, saying that Roger Shawyer's superconducting EM Drive concept did not have side walls.
The answer is that it would NOT be an effective propulsion device, because resonant modes for microwaves produce pressure on the side walls so you cannot get rid of the side walls without microwave energy and pressure escaping laterally. Roger Shawyer's "explanation" that there is no radiation pressure on the side walls of a microwave resonant cavity shows a fundamental misunderstanding of microwave resonant cavities.
The reason why lasers are used in the photonic laser thruster is because lasers have coherent concentrated light so that an optical cavity with lasers does not need nor does it use side walls.
A lot of nonsense can be written about the EM Drive if people fail to differentiate between an optical cavity using lasers and a microwave resonant cavity. (The equation governing the mode shapes for optical cavities are fundamentally different. Optical cavities are not just higher frequency versions of microwave cavities)
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An optical cavity: no side walls
this is fundamentally different from a microwave cavity
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a resonant microwave cavity must have side walls, which are under radiation pressure !
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#3313 by FattyLumpkin on 23 Jun, 2016 20:48
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Dr. Rodal, just to be clear microwaves canNOT be focused in the same way that "lasers have focused concentrated light"? and a resonant mode is?, is not? always present in reflected microwaves between two unconnected mirrors. Other than wavelength and assuming amplitude, band width are equal, in what way is a light wave/photon different from a microwave/photon? Your help is greatly appreciated!
Addendum I guess this all comes down to the question of why microwaves cannot be focused in the same way as light (a laser)? -
#3314 by Mark7777777 on 23 Jun, 2016 21:00
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http://cannae.com/cannae-now-offers-thruster-testing-services/
"Based on industry interest, Cannae now offers testing services for space-based-thruster technologies. Our torsion pendulum and vacuum chamber provide state-of-the-art measurement and calibration capabilities for thrusters generating 200 nN up to 5 mN of force. In the image above, Guido Fetta points to a 1 uN calibrated pulse generated on the loaded torsion pendulum. The high peaks to the left and right of the 1 uN pulse are 5 uN calibrated pulses. Please contact [email protected] for more info." -
#3315 by Rodal on 23 Jun, 2016 21:21
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Dr. Rodal, just to be clear microwaves canNOT be focused in the same way that "lasers have focused concentrated light"? and a resonant mode is?, is not? always present in reflected microwaves between two unconnected mirrors. Other than wavelength and assuming amplitude, band width are equal, in what way is a light wave/photon different from a microwave/photon? Your help is greatly appreciated!
Addendum I guess this all comes down to the question of why microwaves cannot be focused in the same way as light (a laser)?
Read this for example to understand stimulated emission: a Laser: http://sciencequestionswithsurprisinganswers.org/2014/04/17/how-do-you-focus-regular-light-to-make-it-a-laser-beam/
at microwave frequencies: a Maser still needs to have side walls for its resonant cavity:
https://en.wikipedia.org/wiki/Maser
The microwave signal coming out of the hydrogen maser is usually very weak (a few picowatts). Here is a paper on a MASER with a 500MW pulse output: https://inis.iaea.org/search/download.aspx?redURL=http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/39/075/39075005.pdf
The frequency of the signal is fixed and extremely stable. The coherent receiver is used to amplify the signal and change the frequency. This is done using a series of phase-locked loops and a high performance quartz oscillator.
The MASER excites atoms or molecules to generate a chain reaction, or amplification, of photons. To get the proper wavelengths to generate the chain reaction, first electricity or another energy source is "pumped" into a chamber filled with particular atoms or molecules. Then this "pumping" radiation causes the transition of atoms from the ground state to a high energy excited state. From this short-lived state the atoms come down through non-radiative transition to the long-lived metastable state. Once in the metastable state many atoms can be accumulated in one place and in the same state. The MASER beam, stimulated emission, arises when all these accumulated atoms simultaneously make a transition to the ground state, releasing their energy of wavelength l, creating a beam of microwave radiation (or visible light in the case of a LASER) which can be sent on to other atoms to cause the chain reaction . Since all the resulting photons are the same wavelength, MASER beams are extremely focussed and coherent
So if you want to have a microwave thruster for your idea
, you better use a Maser rather than a magnetron 
The magnetron does not provide coherent radiation (no matter Shawyer's misunderstanding of this matter, incorrectly claiming that there is no radiation pressure on the side walls of the EM Drive ). MASERS are much more uncommon than lasers, so be prepared to pay top $$$
No amount of work into a magnetron and polishing the inside of an EM Drive can turn the EM Drive into a maser. (At least the DIY would need to fill the cavity with ammonia, in which case they would need to operate at 24 GHz instead of 2.4 GHz because the emission frequency for Ammonia is at 24 GHz)
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#3316 by Monomorphic on 23 Jun, 2016 21:43
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Build Update: Torsional pendulum improvements walkthrough.
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#3317 by frobnicat on 23 Jun, 2016 22:40
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Dr. Rodal, just to be clear microwaves canNOT be focused in the same way that "lasers have focused concentrated light"? and a resonant mode is?, is not? always present in reflected microwaves between two unconnected mirrors. Other than wavelength and assuming amplitude, band width are equal, in what way is a light wave/photon different from a microwave/photon? Your help is greatly appreciated!
Addendum I guess this all comes down to the question of why microwaves cannot be focused in the same way as light (a laser)?
Beside the specific aspects about stimulated emission and coherence addressed by dr. Rodal's answers I think the confusion stems from not seeing the diffraction limits at work : optical visible light has roughly 5 orders of magnitude smaller wavelength (below 1µm) than 2.45GHz microwaves (122mm). A decimeter sized mirror is enormous compared to wavelength of visible light, so that diffraction has little impact on divergence away from axis at least for the first few ten thousands back and forth "bounces". A cavity could in principle "store" microwaves like an optical cavity without sidewalls but at the condition its end "mirrors" (that could be a fine mesh) are scaled accordingly, that would make for a cavity with typically 10km diameter end mirrors. Distance between end mirrors also plays a role as mirrors very far apart will let an increasing part of light escape even with small diffraction induced beam divergence (that will be a problem with long range photonic laser thruster proposition and beamed propulsion in general : huge mirrors) and the other way closer mirrors may require smaller diameters for a given diffraction divergence leaking. I don't know how to estimate that precisely right now but you get the picture : there is no fundamental difference that would forbid the same geometry as optical cavities for "containment" of microwaves but the scaling would be prohibitive, even if aiming at 24GHz. I think. Dr. Rodal corrects me if wrong, I'm revising old lessons of wave optics here
Any DIYers willing to build 2 Arecibo sized dishes in their backyard to have some experimental check ?
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#3318 by Rodal on 23 Jun, 2016 23:24
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http://cannae.com/cannae-now-offers-thruster-testing-services/
This is not a good sign. People that have been involved with small entreprenural companies know that you spend all your time doing tests and developing the technology as fast as possible, as time is money , otherwise your "sweat capital" is diluted by investors, as more money is needed to continue operations with time without sales, not to say anything about the threat of competitors. A company such as this did not get formed, did not get capital from investors to be doing micro-thruster testing services for others: it got formed to develop a proprietary technology for propellant-less space propulsion and market it as fast as possible.
"Based on industry interest, Cannae now offers testing services for space-based-thruster technologies. Our torsion pendulum and vacuum chamber provide state-of-the-art measurement and calibration capabilities for thrusters generating 200 nN up to 5 mN of force. In the image above, Guido Fetta points to a 1 uN calibrated pulse generated on the loaded torsion pendulum. The high peaks to the left and right of the 1 uN pulse are 5 uN calibrated pulses. Please contact [email protected] for more info."
SpaceX during their development phase did not rent their testing facilities for other companies to test.
By Cannae renting their testing services they are advertising that they don't have enough testing of their own to fully occupy their testing equipment around the clock
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#3319 by JohnFornaro on 24 Jun, 2016 12:13
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All light seems to provide impulses in the form of photons.
Seems? I thought that was proven, particularly in the case of light sails. I'm not following your argument.
, you better use a Maser rather than a magnetron 
The magnetron does not provide coherent radiation (no matter Shawyer's misunderstanding of this matter, incorrectly claiming that there is no radiation pressure on the side walls of the EM Drive ). MASERS are much more uncommon than lasers, so be prepared to pay top $$$