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#2200 by Bob012345 on 30 Oct, 2016 18:12
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But, before dreaming of tons of thrust for flying car and interstellar travel, a proven thrust of 10 grams, comparable with Ion Thrusters, would already be a revolution.
You reject the Demonstrator test report and the confirming review that Roger recently released, showing 8.33g of Thrust force generation (small to big)?
http://www.emdrive.com/DemonstratorTechnicalReportIssue2.pdf
http://www.emdrive.com/ReviewofDMtechreport.pdf
doesn't the scientific method demand independent third parties be able to reproduce the results before it can be verified? an experiment needs to be described clearly with apparatus and instructions. this allows anybody to follow the instructions and achieve the same result. this is more difficult in the case of commercially sensitive or state of the art where the scientist is either withholding vital experiment data or a large budget is required for apparatus. the members of the forum are trying to get to a stage where they can consistently and reliably reproduce any amount of thrust. no small task IMHO
That depends. The Wright brothers didn't need some third party to independently build and fly a plane to scientifically prove their machine worked. Though some believed them right away, most didn't. They needed to fly in front of people and they did but it took till 1908 for enough people to see it to reach a critical point. Their acclaim then happened very suddenly five years after their initial flight. Likewise, when Shawyer announces significant thrust with superconducting EmDrives I would be included to take his word. -
#2201 by Peter Lauwer on 30 Oct, 2016 18:43
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NASA Eagleworks run Neoprene instead of HDPE and PTFE and got very bad force results,
I found this information about experiments with Neoprene nowhere, at least not in the Brady et al., 2014 publication. Is it from 'personal communication'?
Thanks,
Peter -
#2202 by Gilbertdrive on 30 Oct, 2016 19:52
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Not the electrical power, the mechanical power which is F*v such that the thrust then remains constant.
Some toy electric airplane motors deliver about 0.088N/W (27oz for 85W). Given an initial thrust of about 7.5N, the thrust doesn't diminish by a factor of 10 as the plane picks up speed of 10m/s then 20 as the speed gets to 20m/s. It's constant up to and at the equilibrium with the drag. But if the air had zero drag, the acceleration would be constant.
The Shawyer probe is powered at about 200KW with about 30KW going to RF power. The Cannae probe has less than 100W RF power.
Are you serious ? I had hope that you could understand the many explanations that were made about CoE.
The thrust does not necessary diminish by a factor of 10 as the plane multiply it's speed by ten, because it's efficiency can eventually be higher at a higher speed, and the gravity losses needs to be taken into account.
But, considering a motor that has a constant efficiency, and not gravity, of course, it gives a thrust inversely proportional to the speed in the reference frame you are pushing against. It is basic physics. And a motor that has non constant efficiency always will give you a thrust inferior to P/V in the reference frame you are pushing against.
Of course, what complicate the example is that when the plane lifts off, there are much gravity losses.
So accelerating to 10m/s is not much compared to these gravity loses.
Since the Emdrive is new physics, I can understand the claims of constant thrust for constant power, and with mechanical power exceding the power imput. But with classical engines pushing against air, no way.
Also, please, note this important point. The limit P/V does not means, in fact, that the thrust is inversely proportional to the speed. That only means that the thrust best limit is inversely proportional to the speed. But what interests us here is the limit. If your motor is bad at low speed, it can in fact keep the same thrust.
For example, a photon rocket has a terrible efficiency at zero speed. In fact, no work at all. All the energy is lost. The thrust of a photon rocket is not decreasing with speed, because it is already bad enough, it will never exceed P/V. So, the efficiency of a photon rocket is increasing when the speed is increasing in the laboratory reference frame. That keeps the thrust constant. Low but constant.
If you calculate the drag of your little airplane, you can verify easily that the thrust is never superior to P/V (the speed has to be calculated in the reference frame of the air, so the wind has to be taken into account) -
#2203 by ThinkerX on 30 Oct, 2016 19:59
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Interesting Blast from the Past
Yes, this (modification of the wave-pattern in the cavity) happens when a dielectric long enough is placed in a cavity, it also happens in a cylindrical cavity. I had posted a long time ago an exact solution for a dielectric in a cylindrical cavity, in discussions with Notsosureofit showing this behavior. This is a result of solving Maxwell's equations with a dielectric insert, but by itself it does not explain why the EM Drive should accelerate in Space with force/inputPower orders of magnitude larger than a photon rocket, the reason for which still remains to be proved.
Seems that when a dielectric is added to the small end of a TE012 resonant cavity, the distribution of the 2 x 1/2 guide waves changes 180 deg.
In a non dielectric frustum the longest guide wavelengths exist at the small diameter end but when a dielectric is inserted there, the longest guide wavelengths move to the big diameter end as attached.
This guide wavelength swap causes a swap in the radiation pressures on the end plates and in the Thrust force vector direction as per the Purple arrows.
There is experimental data to show this does in fact happen.
It does explain that the dielectric will modify the wave-pattern inside the cavity.
One could further modify the wave-pattern by using a multi-layer dielectric, or a functionally-graded dielectric with electric permittivity changing in the longitudinal direction.
So if somebody has a theory to explain acceleration of the EM Drive in Space without any dielectric, this would show that a dielectric could make the force bigger, or smaller, zero, or change its direction, depending on the placement, dimensions and material properties of the dielectric.
It's almost like the dielectric acts as part of a 'throttle.'
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#2204 by Rodal on 30 Oct, 2016 20:03
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It was communicated by Star-Drive in previous NSF threads: https://forum.nasaspaceflight.com/index.php?action=profile;area=showposts;u=2074NASA Eagleworks run Neoprene instead of HDPE and PTFE and got very bad force results,
I found this information about experiments with Neoprene nowhere, at least not in the Brady et al., 2014 publication. Is it from 'personal communication'?
Thanks,
Peter
due to the not very user-friendly Search facility at NSF, one would have to go through 35 pages of his posts, to find that information
I found this one (just one of several posts on this topic):
https://forum.nasaspaceflight.com/index.php?topic=36313.msg1354582#msg1354582 -
#2205 by meberbs on 30 Oct, 2016 20:36
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Not the electrical power, the mechanical power which is F*v such that the thrust then remains constant.
No, the faster the plane is moving relative to the air, the more power it takes to accelerate the air to produce the same force. Drag is an additional effect. Doing the calculations in different frames (the rest frame of the air, or some other constant velocity frame) will all lead to the same conclusion that the power required to generate a constant force varies with the speed of the air relative to the plane. (which is independent of reference frame, because it is the difference of velocities, so all calculate the same power and force, and that power/ force varies with airspeed.)
Some toy electric airplane motors deliver about 0.088N/W (27oz for 85W). Given an initial thrust of about 7.5N, the thrust doesn't diminish by a factor of 10 as the plane picks up speed of 10m/s then 20 as the speed gets to 20m/s. It's constant up to and at the equilibrium with the drag. But if the air had zero drag, the acceleration would be constant.
The Shawyer probe is powered at about 200KW with about 30KW going to RF power. The Cannae probe has less than 100W RF power.
Example (using a discrete event instead of continuous to make it easier to follow, so energy (E) instead of power, change in momentum (Δp) instead of force. Subscript a means air, p means plane, 1 means initial, 2 means final.
conservation of momentum:
ma*va1 + mp*vp1 = ma*va2 + mp*vp2
Δp = -ma*(va2 - va1 ) = mp*(vp2 - vp1 )
conservation of energy:
0.5*ma*va12 + 0.5*mp*vp12 + E = 0.5*ma*va22 + 0.5*mp*vp22
Rearrange to solve for E, group the terms, and apply a2-b2 = (a+b)(a-b) pull out the parts which are equal to Δp, and you get:
E = 0.5*Δp*( (vp2 - va2) + (vp1 - va1) )
Therefore, for a constant change in the plane's momentum, the engine needs to output more energy if the plane's airspeed is higher, and all frames agree on this amount of energy, since it comes from frame-independent potential energy (chemical/electrical).
In any real system, there are many other complications (temperature changes, motor efficiency as function of RPM etc.), but this effect will still be there. -
#2206 by zen-in on 30 Oct, 2016 20:36
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Was good enough for the UK gov to award Roger more funding to build the rotary test rig.
They funded him to make more tests. It confirms that the first tests were enough interesting to call more tests, but not enough strong to go directly to the application. It means that more tests were needed.
Not correct.
The 1st funds were for the Experimental EmDrive and to do static Thrust force generation tests, which was verified as working as claimed.
The 2nd round of funds were to construct the Demonstrator EmDrive and do static Thrust force generation tests, which was verified as working as claimed.
The 3rd round of funds were to construct the Rotary test rig and conduct dynamic Reaction force generation / acceleration tests, which was verified as working as claimed.
Each funding program was self contained and the claimed results had to be verified.
Have you read the 2 test reports and the independent review's comments?
This is all ancient history; more than 10 years old. Shawyer has not proven anything conclusive despite all the UK taxpayer money he has spent. He wasn't able to convince those who funded his research of over 10 years ago that he could create a force with microwave power using room temperature materials so why should anyone believe an em-drive made from high temperature superconductors (HTS) would work? The goal should be to provide proof of this theory as it was originally stated. Shawyer should provide conclusive proof the em-drive produces thrust. There have been a lot of claims but no proof to any of these claims. I think it's good that people are experimenting. We all have to be skeptical; especially the experimenter. -
#2207 by SeeShells on 30 Oct, 2016 21:31
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https://forum.nasaspaceflight.com/index.php?topic=36313.msg1378069#msg1378069NASA Eagleworks run Neoprene instead of HDPE and PTFE and got very bad force results,
I found this information about experiments with Neoprene nowhere, at least not in the Brady et al., 2014 publication. Is it from 'personal communication'?
Thanks,
Peter
Shell -
#2208 by TheTraveller on 31 Oct, 2016 11:26
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Interesting data from Roger's 2009 paper on his Experimental YBCO thruster where he published experimentally measured surface resistance data for YBCO on Sapphire data at 3.83GHz. He also stated the experimentally measured Qu was 6.8x10^6, cooled with LN2, which would produce a specific force of 41N/kWrf, increasing to 145N/kWrf if cooled by LHe.
I then plotted the results for cooling with LH2 and LHe as attached.
He further states in the paper that the data was from his 1st Experimental cryo EmDrive and that he has moving to build a Demonstrator EmDrive, following the development process and names of the non cryo EmDrives.
That was in 2009. Now in late 2016 Roger has released a radical cryo EmDrive, that based on the cavity TC from the Force generation curves, would have a Ql of ~3x10^9 and specific force of ~10,000N/kWrf. Seems Roger has been busy.
Several here have stated YBCO will not work at microwave frequencies. Seems their opinion may need to be updated.
143kg/6kWrf is a specific force of 234N/kWrf which is not that far above the 145N/kWrf figure for LHe cooling of the Experimental cryo EmDrive data.
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#2209 by PotomacNeuron on 31 Oct, 2016 13:40
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Interesting data from Roger's 2009 paper on his Experimental YBCO thruster where he published experimentally measured surface resistance data for YBCO on Sapphire data at 3.83GHz. He also stated the experimentally measured Qu was 6.8x10^6, cooled with LN2, which would produce a specific force of 41N/kWrf, increasing to 145N/kWrf if cooled by LHe.
I then plotted the results for cooling with LH2 and LHe as attached.
He further states in the paper that the data was from his 1st Experimental cryo EmDrive and that he has moving to build a Demonstrator EmDrive, following the development process and names of the non cryo EmDrives.
That was in 2009. Now in late 2016 Roger has released a radical cryo EmDrive, that based on the cavity TC from the Force generation curves, would have a Ql of ~3x10^9 and specific force of ~10,000N/kWrf. Seems Roger has been busy.
Several here have stated YBCO will not work at microwave frequencies. Seems their opinion may need to be updated.
143kg/6kWrf is a specific force of 234N/kWrf which is not that far above the 145N/kWrf figure for LHe cooling of the Experimental cryo EmDrive data.
Would you please make it clear that the "41N/kWrf", "145N/kWrf", "~10,000N/kWrf", "143kg/6kWrf", "234N/kWrf" are all speculated based on Q and are not actually measured? I think many may not read carefully enough and may get incorrect impression.
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#2210 by TheTraveller on 31 Oct, 2016 13:59
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Interesting data from Roger's 2009 paper on his Experimental YBCO thruster where he published experimentally measured surface resistance data for YBCO on Sapphire data at 3.83GHz. He also stated the experimentally measured Qu was 6.8x10^6, cooled with LN2, which would produce a specific force of 41N/kWrf, increasing to 145N/kWrf if cooled by LHe.
I then plotted the results for cooling with LH2 and LHe as attached.
He further states in the paper that the data was from his 1st Experimental cryo EmDrive and that he has moving to build a Demonstrator EmDrive, following the development process and names of the non cryo EmDrives.
That was in 2009. Now in late 2016 Roger has released a radical cryo EmDrive, that based on the cavity TC from the Force generation curves, would have a Ql of ~3x10^9 and specific force of ~10,000N/kWrf. Seems Roger has been busy.
Several here have stated YBCO will not work at microwave frequencies. Seems their opinion may need to be updated.
143kg/6kWrf is a specific force of 234N/kWrf which is not that far above the 145N/kWrf figure for LHe cooling of the Experimental cryo EmDrive data.
Would you please make it clear that the "41N/kWrf", "145N/kWrf", "~10,000N/kWrf", "143kg/6kWrf", "234N/kWrf" are all speculated based on Q and are not actually measured? I think many may not read carefully enough and may get incorrect impression.
The Qu of 6.8x10^6 and Rs of 78 uOhm for the YBCO on Sapphire thin film at 77K and 3.83GHz are experimentally measured values.
There are established equations that link the other values together. One follows the other as does Ohm's law. Shall I then question every Ohm's law calculation because it has not been experimentally measured?
Roger measured the Qu in his 1st experimental YBCO EmDrive and then measured the surface resistance change vs temp at 3.82GHz. It is simple math to do the calc at other values of Rs once the Qu vs Rs at one temp is known.
This is known as EmDrive Engineering 101. -
#2211 by zen-in on 31 Oct, 2016 14:00
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Interesting data from Roger's 2009 paper on his Experimental YBCO thruster where he published experimentally measured surface resistance data for YBCO on Sapphire data at 3.83GHz. He also stated the experimentally measured Qu was 6.8x10^6, cooled with LN2, which would produce a specific force of 41N/kWrf, increasing to 145N/kWrf if cooled by LHe.
I then plotted the results for cooling with LH2 and LHe as attached.
He further states in the paper that the data was from his 1st Experimental cryo EmDrive and that he has moving to build a Demonstrator EmDrive, following the development process and names of the non cryo EmDrives.
That was in 2009. Now in late 2016 Roger has released a radical cryo EmDrive, that based on the cavity TC from the Force generation curves, would have a Ql of ~3x10^9 and specific force of ~10,000N/kWrf. Seems Roger has been busy.
Several here have stated YBCO will not work at microwave frequencies. Seems their opinion may need to be updated.
143kg/6kWrf is a specific force of 234N/kWrf which is not that far above the 145N/kWrf figure for LHe cooling of the Experimental cryo EmDrive data.
In Shawyer's paper he states the surface resistivity data is "based on specified manufacturer's data" (quoted from his paper). In all probability he does not possess any of the sapphire substrate HTS described in his paper and he has not built the device you describe as "an experimental HTS thruster" There are thousands of papers published every year devoted to esoteric measurements of small sections of HTS in carefully controlled laboratory setups. Shawyer has extrapolated from that with his claim an HTS em-drive thruster is possible and you have taken a much bigger leap by claiming he has built "an experimental HTS thruster". -
#2212 by TheTraveller on 31 Oct, 2016 14:08
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Interesting data from Roger's 2009 paper on his Experimental YBCO thruster where he published experimentally measured surface resistance data for YBCO on Sapphire data at 3.83GHz. He also stated the experimentally measured Qu was 6.8x10^6, cooled with LN2, which would produce a specific force of 41N/kWrf, increasing to 145N/kWrf if cooled by LHe.
I then plotted the results for cooling with LH2 and LHe as attached.
He further states in the paper that the data was from his 1st Experimental cryo EmDrive and that he has moving to build a Demonstrator EmDrive, following the development process and names of the non cryo EmDrives.
That was in 2009. Now in late 2016 Roger has released a radical cryo EmDrive, that based on the cavity TC from the Force generation curves, would have a Ql of ~3x10^9 and specific force of ~10,000N/kWrf. Seems Roger has been busy.
Several here have stated YBCO will not work at microwave frequencies. Seems their opinion may need to be updated.
143kg/6kWrf is a specific force of 234N/kWrf which is not that far above the 145N/kWrf figure for LHe cooling of the Experimental cryo EmDrive data.
In Shawyer's paper he states the surface resistivity data is "based on specified manufacturer's data" (quoted from his paper). In all probability he does not possess any of the sapphire substrate HTS described in his paper and he has not built the device you describe as "an experimental HTS thruster" There are thousands of papers published every year devoted to esoteric measurements of small sections of HTS in carefully controlled laboratory setups. Shawyer has extrapolated from that with his claim an HTS em-drive thruster is possible and you have taken a much bigger leap by claiming he has built "an experimental HTS thruster".
He states he built an Experimental cryo YBCO on Sapphire EmDrive thruster. Even shared a photo.
Minus the 2 images (Fig 12 and Fig 13) here is what Roger wrote:Quote7.SUPERCONDUCTING DEMONSTRATOR PROGRAMME
The first phase of this programme was an experimental superconducting thruster. This low power, HTS device operates at liquid nitrogen temperature, and is designed for very high Q and consequently high specific thrust.
Fig 12 Experimental Superconducting Thruster as attached
Fig 12 shows the thruster, which operates at 3.8 GHz, and was designed using an update of the software used for the previous S band designs. Super-conducting surfaces are formed from YBCO thin films on sapphire substrates.
Small signal testing at 77 deg K confirmed the design, with a Q of 6.8x10^6 being measured.
Fig 13 shows the surface resistivity of the superconducting thruster based on specified manufacturer’s data, updated for the measured data.
Fig 13 Surface Resistivity as attached.
For the Demonstrator Thruster, cooling will be by liquid hydrogen. The design resistivity at 20deg K is therefore taken as 11.8 x 10-6 Ohms. This value was then used in the same design software used for the experimental 2G thruster. The resulting thrust was calculated as 143kg for 6kW input.
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#2213 by Bob012345 on 31 Oct, 2016 16:16
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No, the engine puts out a fixed power and thrust. The plane then accelerates to its max speed for that power and is in a steady state. It's all very simple but you're over complicating it. According to you, the thrust drops the instant the plane moves. Not true. But this isn't a perfect example since the air defines a fixed frame.Not the electrical power, the mechanical power which is F*v such that the thrust then remains constant.
No, the faster the plane is moving relative to the air, the more power it takes to accelerate the air to produce the same force. Drag is an additional effect. Doing the calculations in different frames (the rest frame of the air, or some other constant velocity frame) will all lead to the same conclusion that the power required to generate a constant force varies with the speed of the air relative to the plane. (which is independent of reference frame, because it is the difference of velocities, so all calculate the same power and force, and that power/ force varies with airspeed.)
Some toy electric airplane motors deliver about 0.088N/W (27oz for 85W). Given an initial thrust of about 7.5N, the thrust doesn't diminish by a factor of 10 as the plane picks up speed of 10m/s then 20 as the speed gets to 20m/s. It's constant up to and at the equilibrium with the drag. But if the air had zero drag, the acceleration would be constant.
The Shawyer probe is powered at about 200KW with about 30KW going to RF power. The Cannae probe has less than 100W RF power.
Example (using a discrete event instead of continuous to make it easier to follow, so energy (E) instead of power, change in momentum (Δp) instead of force. Subscript a means air, p means plane, 1 means initial, 2 means final.
conservation of momentum:
ma*va1 + mp*vp1 = ma*va2 + mp*vp2
Δp = -ma*(va2 - va1 ) = mp*(vp2 - vp1 )
conservation of energy:
0.5*ma*va12 + 0.5*mp*vp12 + E = 0.5*ma*va22 + 0.5*mp*vp22
Rearrange to solve for E, group the terms, and apply a2-b2 = (a+b)(a-b) pull out the parts which are equal to Δp, and you get:
E = 0.5*Δp*( (vp2 - va2) + (vp1 - va1) )
Therefore, for a constant change in the plane's momentum, the engine needs to output more energy if the plane's airspeed is higher, and all frames agree on this amount of energy, since it comes from frame-independent potential energy (chemical/electrical).
In any real system, there are many other complications (temperature changes, motor efficiency as function of RPM etc.), but this effect will still be there. -
#2214 by Bob012345 on 31 Oct, 2016 17:08
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Not the electrical power, the mechanical power which is F*v such that the thrust then remains constant.
Some toy electric airplane motors deliver about 0.088N/W (27oz for 85W). Given an initial thrust of about 7.5N, the thrust doesn't diminish by a factor of 10 as the plane picks up speed of 10m/s then 20 as the speed gets to 20m/s. It's constant up to and at the equilibrium with the drag. But if the air had zero drag, the acceleration would be constant.
The Shawyer probe is powered at about 200KW with about 30KW going to RF power. The Cannae probe has less than 100W RF power.
Are you serious ? I had hope that you could understand the many explanations that were made about CoE.
The thrust does not necessary diminish by a factor of 10 as the plane multiply it's speed by ten, because it's efficiency can eventually be higher at a higher speed, and the gravity losses needs to be taken into account.
But, considering a motor that has a constant efficiency, and not gravity, of course, it gives a thrust inversely proportional to the speed in the reference frame you are pushing against. It is basic physics. And a motor that has non constant efficiency always will give you a thrust inferior to P/V in the reference frame you are pushing against.
Of course, what complicate the example is that when the plane lifts off, there are much gravity losses.
So accelerating to 10m/s is not much compared to these gravity loses.
Since the Emdrive is new physics, I can understand the claims of constant thrust for constant power, and with mechanical power exceding the power imput. But with classical engines pushing against air, no way.
Also, please, note this important point. The limit P/V does not means, in fact, that the thrust is inversely proportional to the speed. That only means that the thrust best limit is inversely proportional to the speed. But what interests us here is the limit. If your motor is bad at low speed, it can in fact keep the same thrust.
For example, a photon rocket has a terrible efficiency at zero speed. In fact, no work at all. All the energy is lost. The thrust of a photon rocket is not decreasing with speed, because it is already bad enough, it will never exceed P/V. So, the efficiency of a photon rocket is increasing when the speed is increasing in the laboratory reference frame. That keeps the thrust constant. Low but constant.
If you calculate the drag of your little airplane, you can verify easily that the thrust is never superior to P/V (the speed has to be calculated in the reference frame of the air, so the wind has to be taken into account)
The basic point is that you say the EmDrive, if it works at all, will stop accelerating as it's kinetic energy grows faster than its electrical energy input. You're claiming you know Shawyer, Fetta and anyone else who shows a fixed thrust for a fixed electrical power doesn't understand how physics works if they claim that acceleration will just continue. Myself and others believe if it works at all, nothing can limit the acceleration since all observer frames are arbitrary. I believe the energy conundrum is only an apparent violation.
Velocity is relative but acceleration is absolute. Thus, if the EmDrive works, it produces a force and thus an acceleration regardless of anything. There is no way for it to "know" what velocity it's going such as to "know" it's kinetic energy is in danger of growing at a rate beyond which the power it is supplying can handle. The only limitation must be that the force it produces is proportional to the power it uses to produce that force which is the point Woodward made. -
#2215 by Bob012345 on 31 Oct, 2016 17:12
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Interesting data from Roger's 2009 paper on his Experimental YBCO thruster where he published experimentally measured surface resistance data for YBCO on Sapphire data at 3.83GHz. He also stated the experimentally measured Qu was 6.8x10^6, cooled with LN2, which would produce a specific force of 41N/kWrf, increasing to 145N/kWrf if cooled by LHe.
I then plotted the results for cooling with LH2 and LHe as attached.
He further states in the paper that the data was from his 1st Experimental cryo EmDrive and that he has moving to build a Demonstrator EmDrive, following the development process and names of the non cryo EmDrives.
That was in 2009. Now in late 2016 Roger has released a radical cryo EmDrive, that based on the cavity TC from the Force generation curves, would have a Ql of ~3x10^9 and specific force of ~10,000N/kWrf. Seems Roger has been busy.
Several here have stated YBCO will not work at microwave frequencies. Seems their opinion may need to be updated.
143kg/6kWrf is a specific force of 234N/kWrf which is not that far above the 145N/kWrf figure for LHe cooling of the Experimental cryo EmDrive data.
If he measured such a large force why can't he just say that? It seems such a large force would knock over his apparatus. -
#2216 by wicoe on 31 Oct, 2016 17:28
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Velocity is relative but acceleration is absolute. Thus, if the EmDrive works, it produces a force and thus an acceleration regardless of anything. There is no way for it to "know" what velocity it's going such as to "know" it's kinetic energy is in danger of growing at a rate beyond which the power it is supplying can handle. The only limitation must be that the force it produces is proportional to the power it uses to produce that force.
If the EmDrive works by "pushing" against something (i.e. some unknown field or other objects in the universe via gravity assist), it perfectly "knows" its velocity relative to the medium/objects it's pushing against. And just like with any other "pushing" mechanism, the higher your velocity, the harder it is to push. This is required for CoM/CoE to be observed, as has been explained multiple times in this thread. -
#2217 by Bob012345 on 31 Oct, 2016 17:37
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You've just defined a fixed absolute frame for the universe, something Relativity forbids. What would be required for CoM/CoE preservation is that the pushing is the same in all frames. In effect, every frame is equivalent and can be "pushed" against equally. Every frame of the universe must be the Center of Momentum frame.Velocity is relative but acceleration is absolute. Thus, if the EmDrive works, it produces a force and thus an acceleration regardless of anything. There is no way for it to "know" what velocity it's going such as to "know" it's kinetic energy is in danger of growing at a rate beyond which the power it is supplying can handle. The only limitation must be that the force it produces is proportional to the power it uses to produce that force.
If the EmDrive works by "pushing" against something (i.e. some unknown field or other objects in the universe via gravity assist), it perfectly "knows" its velocity relative to the medium/objects it's pushing against. And just like with any other "pushing" mechanism, the higher your velocity, the harder it is to push. This is required for CoM/CoE to be observed, as has been explained multiple times in this thread. -
#2218 by wicoe on 31 Oct, 2016 17:50
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You've just defined a fixed absolute frame for the universe, something Relativity forbids.
This is a misunderstanding of the principle of relativity. If you were in a 100% closed ref frame not interacting with the outside world, you wouldn't be able to tell whether you're moving or not. However, the primary (and only?) way for devices like EmDrive to not violate CoM/CoE is to interact with the outside world (i.e. fields, galaxies, etc). There is an "absolute" frame in which the cosmic background radiation is "at rest". By measuring the CMB, you can tell how you're moving relative to that frame. -
#2219 by Bob012345 on 31 Oct, 2016 17:56
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You've just defined a fixed absolute frame for the universe, something Relativity forbids.
This is a misunderstanding of the principle of relativity. If you were in a 100% closed ref frame not interacting with the outside world, you wouldn't be able to tell whether you're moving or not. However, the primary (and only?) way for devices like EmDrive to not violate CoM/CoE is to interact with the outside world (i.e. fields, galaxies, etc). There is an "absolute" frame in which the cosmic background radiation is "at rest". By measuring the CMB, you can tell how you're moving relative to that frame.
The CMB does not define an absolute reference frame of the universe in the sense you want. I'm not saying there is no interaction with the universe, just that the CMB is not some absolute frame that defines that interaction. Whatever the interactions, it's not going to be frame dependent. It's going to be invariant.
Think of that interaction like a magic rocket that has a fixed thrust but never runs out of fuel and never losses mass. There is always an exhaust to react against and every frame validates CoE and CoM.
