Author Topic: EM Drive Developments - related to space flight applications - Thread 2  (Read 2172176 times)

Offline ThinkerX

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Well, Edison was one of the greatest inventors.  He was completely self-taught (with visits to the Cooper Union). Edison was born only 16 years after Maxwell.  Edison was responsible for some of the greatest electromagnetic inventions ever, yet he was not a theoretical physicist like Maxwell or Hertz. Who was the inventor? Edison or Maxwell?.    Why should Shawyer  be the one expected to explain the physics of why it works (if it does work)?

People here and elsewhere say a coherent theory is needed in order to advance with this project.

Seems to me, what Shawyer is doing is amassing a pile of data from differing versions of the EM Drive.  If those results could somehow be reconciled with mainstream physics, even if it means tweaking Relativity or some such, then a workable theory is that much closer.  Or to phrase it a bit differently, Shawyer probably has the data, but the data needs interpretation by somebody with a different skill set.   He definitely seems to be ahead of everybody else in EM drive development. 

Offline Rodal

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Well, Edison was one of the greatest inventors.  He was completely self-taught (with visits to the Cooper Union). Edison was born only 16 years after Maxwell.  Edison was responsible for some of the greatest electromagnetic inventions ever, yet he was not a theoretical physicist like Maxwell or Hertz. Who was the inventor? Edison or Maxwell?.    Why should Shawyer  be the one expected to explain the physics of why it works (if it does work)?

People here and elsewhere say a coherent theory is needed in order to advance with this project.

...
The majority of contributors to this thread say that what's needed are much more experiments: mainly to confirm that the thrust is real or to nullify it, by verifying the experiments at another NASA center (Glenn or JPL) and a univeristy (John Hopkins, for example) and put this EM Drive phenomena to bed, or continue its engineering progress.  Actually a number of contributors are planning their own experiments and have shown photographs of their progress.  The number of experiments conducted for the EM Drive and the R&D budget are infinitesimal compared with the number of experiments regularly conducted in R&D projects both commercial, academic or government agency and in comparison with normal R&D budgets.  Not a single experiment has been conducted at a US or European University.  Here are a number of experiments that could be conducted:  cylindrical cavity without dielectric, cylindrical cavity with cylindrical dielectric, cylindrical cavity with conical dielectric, truncated cone with one end made of cast iron, truncated cone made with one end internally coated with thin film of Metglas, truncated cone made with Aluminum instead of copper, comparison of excitation produced by Gunn diode, magnetron, etc.; examination of thrust force vs. cone angle of truncated cone, examination of thrust force in a cone (untruncated) cavity. Should I continue?
« Last Edit: 02/28/2015 03:25 PM by Rodal »

Offline JPLeRouzic

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It's to bad that we can't find a way that one of the little known or unknown solutions to Maxwell's equations can cause  a momentum.
There is obviously momentum in electromagnetic waves. There are also some little known electromagnetic effects that create torque.

http://arxiv.org/abs/0807.1310

What do you mean? It's known since 19th century there is momentum in electromagnetic waves. It's not something new.

Quote
Quoting @Aero
Quote
Unless of course it is surface electrons excited by the high power resonant RF, tunnelling through the 35 micron copper ends.
Quoting @JPLeRouzic
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Yes, and many other things may happen were not tested nor even proposed. I wonder how people can know that a lot of energy is pumped in this device and imagine nothing will get out. At the very least thermal effects should happen. Testing it in (near) vacuum doesn't eliminate the thermal hypothesis. Even Pioneer's acceleration that was due to thermal effects after all: http://spectrum.ieee.org/aerospace/astrophysics/finding-the-source-of-the-pioneer-anomaly
Another thing that strikes me is that people search for a unique cause explaining everything, which is a bit unlikely.

One last thought: If a simulator shows results, build this device and publish results in a mainstream conference. Interesting things may happen ;-)

There are absolutely thermal effects. For every watt pumped in, you get that much heat out as IR. An RF dummy load is an efficient converter of RF to heat. The systemic effects slide with the dummy load attached is the control for heat. Thermal artifacts were a major area of exploration in both threads. Paul March provided lots of data to show that thermal effects were extensively studied over at Eagleworks. There's a thermal analysis on this thread, one of many indications that heat was controlled for: http://forum.nasaspaceflight.com/index.php?topic=36313.msg1326997#msg1326997 Plus the math that has been done numerous times for a photon rocket doesn't add up. So the vacuum did eliminate the thermal hypothesis.
5*10-6 Torr is hardly a vacuum good enough to eliminate the thermal hypothesis. That's what you encounter at 1000 km high or so.
Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects.


Offline flux_capacitor

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Great find and thanks  :)  for bringing it to our attention, this is the first time I see this patent.

Very thought provoking, and interesting in its own right.

I note that Shawyer's patent was file in 1988 !, that's 27 years ago !

This man has been working at this for a long, long time

You're welcome. To my knowledge Roger Shawyer filed 4 patent applications related to the EmDrive, here they are attached at the bottom of this message. I think everyone who'd want to replicate this work should read them first.

- GB application 2229865, Shawyer, Roger John, "Electrical propulsion unit for spacecraft", filed 1st November 1988, published 3 October 1990
- GB application 2334761, Shawyer, Roger John, "Microwave thruster for spacecraft", filed 29 April 1988, published 1st September 1999.
- GB application 2399601, Shawyer, Roger John, "Thrust producing device using microwaves", file 13 March 2003, published 22 September 2004
- GB application 2493361, Shawyer, Roger John, "A high Q microwave radiation thruster", filed 1st August 2011, published 6 February 2013

You'll notice the 1999 patent (the second one, with a truncated cone cavity and an internal truncated cone dielectric) was actually the first filed, more than ten years before publication. He was followed by the filling of the patent with the cylindrical cavity only six months later, but nine years separated the two publications.

IMHO the problem with Shawyer and the scientific community which has not even given the EmDrive a try in the past 25 years (!) is not with the EmDrive itself as an experiment, but with Shawyer's attempts to explain the anomalous thrust (i.e. propellantless thrust and the conservation issues it implies) in terms of a radiation pressure imbalance, where a relativistic effect would be caused on end plates by the action of group velocity in different frames of reference (see his theory paper). Some scientists strongly disagree with that explanation. But this does not imply the EmDrive does not work and could be explained otherwise. Your comment about Edison illustrates the situation well.

We can't judge Shawyer too badly for his theoretical paper, as he is an engineer, not a physicist. Most importantly, the contract he signed with UK government Department of Trade and Industry in July 2001, to develop the EmDrive, specifically asked him to write such a document for the preliminary analysis phase.

We are lucky Shawyer even published some data as patents and conference papers. Well, obviously he needed some money to start all this and he had to publicize his work at that time. He regularly presented progress in experiments at various international conferences, in Brighton in 2005 [1]; at the 59th International Astronautical Congress (IAC) in Glasgow in 2008 [2]; the CEAS 2009 European Air and Space Conference held in Manchester [3]; the 2nd Conference on Disruptive Technology in Space Activities (TECHNO DIS) at CNES' Toulouse Space Show, France in 2010 [4]; IAC 2013 in Beijing, China [5][6]; and IAC 2014, Toronto, Canada [7].

I wonder how the tests of superconducting cavities with very high Q are going on now. I emailed Shawyer to ask some information about Chinese cavity dimensions and other news, but he closed the tap and politely declined to comment. After all, he runs a private company (SPR Ltd) and wants to make money of this, so I think he won't disclose sensitive information any further. We'll see.

Guido P. Fetta also silently runs a private company (Cannae LLC) and has an approach different than a tapered frustum and dielectrics.

The Chinese team publishes information in peer-reviewed academic journals, but we are not protected against any disinformation or cover-up by the military if they make a real breakthrough. Pr. Juan Yang also declines to comment any other information than what she already published.

Eagleworks publish their results as regular reports and conference papers, and it's a very good thing. Moreover Paul March kindly shares additional information and wise thinking here with us. Too bad this research is not better funded by NASA. Having such a close deadline for results (end of March 2015 if I remember) and being slowed down by dying power amplifiers, not having the funds to just repair or change them, is really a shame for Science and maybe also for the future of mankind.

So it is a very good thing now some people express willpower to conduct independent verification and validation of such a potential disruptive technology in their own lab.

Offline Left Field

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Hi. Newcomer here but I have been following since thread 1. Hats off to all of you and your dedication to finding answers - it is massively entertaining.

I just saw a new post by dustinthewind in Advanced Concepts and thought it may be related:

http://forum.nasaspaceflight.com/index.php?topic=36911.0

It contains links to a patent with the following abstract:

Quote
An electronic propulsion engine that creates a propulsive force or thrust using forces or electrostatic electromagnetic forces, with an effect that is similar to the thrust of a jet or rocket engine. Forces are generated using electromagnets or capacitor plates that are separated by dielectric spacer cores and are operated with two modulated currents. The two modulated currents are synchronized, but with a relative phase such that the forces on the two magnets or capacitor plates are not balanced. Included are techniques to reduce circuit impedance and control field dispersion, such as tuned LCR circuits, dielectric core materials between the magnets or capacitor plates, and RF superconductors result in high propulsion efficiencies. The system operates at RF frequencies and can also be used as a communication device.

Offline Rodal

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Hi. Newcomer here but I have been following since thread 1....
Welcome to this thread  :)
« Last Edit: 02/28/2015 02:15 PM by Rodal »

Offline Rodal

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...To my knowledge Roger Shawyer filed 4 patent applications related to the EmDrive, here they are attached at the bottom of this message....

What an excellent post, full of information, with attached documents and very well-written  :)  Thanks !

Offline Star-Drive

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Dr. Rodal & Crew:

The Eagleworks team has already build a 6061 aluminum frustum cavity with 1/4" thick walls and O-ring end caps meant to hold a 1 Bar pressure differential with internal nickel/copper/silver/gold plating system on all interior surfaces with plating thickness of 10-to-15 microns for the first three layers and 0.5 microns for exposed to the RF gold layer.  Sadly the gold layer was just as thick as the rest of the plated layers and textured as well, so as far as the applied ~2.0 GHz RF was concerned it was only interacting with the rough gold layer.  This had the effect of cutting the resonant Q-factor for this aluminum frustum by almost a factor of three over our copper frustum for the resonances of interest. 

At the same time we also tried using a smaller volume, higher-K (e-r=~40) ceramic dielectric resonator discs in the Al cavity mounted at its small OD end, while driving it at its TE011 mode if memory serves.  Bottom line was that this configuration was a total bust in regards to thrust production in our torque pendulum system running at this resonant mode.  This aluminum frustum design also turned out to be ~4X times the mass of the thin walled copper cavity even while using lower density aluminum for its construction.  This exercise was a tribute to the fact that one should never ASSUME that you know what you are doing until proven otherwise!  And oh yes, and only try one variation in the design at a time or one will get lost, fast!

Best, Paul M.
Star-Drive

Offline Rodal

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So the vacuum did eliminate the thermal hypothesis.
...
5*10-6 Torr is hardly a vacuum good enough to eliminate the thermal hypothesis. That's what you encounter at 1000 km high or so.
Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects.


@Mulletron must have meant "So the vacuum did eliminate the [natural convection] thermal hypothesis" .  He wrote "thermal hypothesis" without the words "natural convection" because he thought that it was obviously understood he was referring to convection in the context he was discussing:  what is the difference between ambient pressure and  5*10-6 Torr.  Obviously this pressure makes a huge difference for natural convection currents, as a trivial calculation can show that 5*10-6 Torr vacuum does eliminate the natural convection hypothesis that was advanced in most media (including Prof. Baez's blog) as the most likely explanation for the measurements.  @Frobnicat, was proposing the thermal convection hypothesis as a possible artifact, and he worked some equations in Thread 1.  I do not recall @Frobnicat objecting to a 5*10-6 Torr vacuum nullifying the hypothesis of natural thermal convection from the EM Drive being able to produce the measured forces. 


Concerning <<Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects>>, yes the Pioneer anomaly was successfully explained by a team of JPL engineers/scientists on the basis of thermal radiation effects (not natural convection thermal effects). 

Thermal radiation, an entirely different (from convection) means of thermal transport, will take place even in a perfect vacuum, as thermal radiation is electromagnetic radiation and therefore does not need a gas or a fluid as a transport medium.  On the other hand natural convection is completely dependent on fluid or gas medium to carry it, and without a fluid or a gas, there cannot be any thermal convection.  Thermal convection involves fluid advection.

Radiative heat transfer is the only form of heat transfer that can take place in a vacuum.  Radiative heat transfer depends on the difference between the fourth power of the temperatures between the radiating surface and the irradiated surface, the surface areas and the emissivities of the radiating and irradiated surfaces and the Stefan–Boltzmann constant .  It may be important for the Pioneer anomaly: an extremely small effect comprising an acceration towards the Sun, of only 8.74×10^(−10) m/s^2, due to asymmetrical radiation of heat from the Radioisotope thermoelectric generators or from the spacecraft electronics reflecting from the back of the spacecraft's dish-like main antenna, causing a recoil like sunlight striking a solar sail.

But in the case of the EM Drive, how much does the temperature difference between radiated and irradiated surfaces have to be to to justify the measured thrust forces ?
« Last Edit: 02/28/2015 06:23 PM by Rodal »

Offline MathieuA

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http://www.ebay.com/itm/AERCOM-Microwave-RF-Isolator-Circulator-2-4GHz-20dB-isolation-Low-I-L-TESTED-/281549538390?ssPageName=ADME:L:OU:US:1120
Picked up one of these puppies on Ebay to protect my amp. Another example of broken time reversal symmetry in action.

Got about an oz of very expensive liquid metal from here:
http://www.amazon.com/Gallium-Indium-Eutectic-GaInSn-68-5%25/dp/B00KN92MWW/ref=sr_1_3?ie=UTF8&qid=1425074693&sr=8-3&keywords=galinstan

So back to the copper from way back: http://forum.nasaspaceflight.com/index.php?topic=36313.msg1326742#msg1326742
...
Been working with the supplier with a machine shop I posted about way back:
http://forum.nasaspaceflight.com/index.php?topic=36313.msg1326669#msg1326669
I'm going that route. The quote I got is: price: $120.00 layout + $51.63 for part + freight. So I have to pay the layout, then anyone else who wants one of these:

but built in 16oz copper, with a smooth butt seam inside, and 1/4" flange around edges, can get one for about 50 bucks plus shipping. If all this works out, it'll fulfill my goal of making a replication by DIYers easier. For me, paying the layout plus price about breaks even with buying the sheet myself and fumblefuddeling around trying to solder up a cone at home. So I'm happy. I'll get back with more later, when the items are at home.

Hello Mulletron,

Hope you'll be able to conduct another test, and I guess there are many other people like me who encourage you to continue.
How do you intend to measure the (very tiny) thrust ? Reading back NASA's paper, it seems they had to run the experiment in a lab with complex (and expensive) tools to remove all parasite effects that would interfere with the thrust from the apparatus. Maybe you have access to such equipment ?

--
Mathieu

Offline flux_capacitor

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How do you intend to measure the (very tiny) thrust ? Reading back NASA's paper, it seems they had to run the experiment in a lab with complex (and expensive) tools to remove all parasite effects that would interfere with the thrust from the apparatus. Maybe you have access to such equipment ?

- Roger Shawyer achieved a thrust of 174 mN @ 450 W of input power in 2010 (he then operated its engine up to 600 W but thrust levels are not known fort that power).
- Chinese NWPU achieved 720 mN @ 2500 W in 2010.
- Eagleworks achieved 116 µN @ 17 W in 2014.

So if you're gonna try an EmDrive at home, you'd better feed it with at least severals hundred of watts of electric power to be able to measure tens to hundreds of millinewtons. Staying below 100 W seems to produce thrusts in the micronewton range, way too low and something only a dedicated lab like Eagleworks can detect with expensive apparatus. At that level you detect any low-frequency vibrations like small seismic events. Indeed you noticed in the paper that Eagleworks used an isolated test rig from the Apollo program era with an extremely sensitive torsion pendulum, and on windy days they were able to detect the waves from the Gulf of Mexico, about 25 miles southeast of JSC… This low-power experiment was intended for a specific purpose: test the EmDrive in a hard vacuum. Only a small device with a compact and light onboard power amplifier could be tested, hence the very low power used compared to previous experiments by Shawyer and the Chinese.

The Chinese pursue a different path: they try to brutally produce the maximum thrust available with cheap but high power magnetrons. This way they cannot eliminate convection current or test their drive in a hard vacuum, but they can show the thrust achieved is too high to be accounted only for trivial reasons. Besides they showed the engine could compete with modern ion thrusters and perhaps one day overtake them.

You can also let the test article rotate. But it's not easy. Shawyer conducted such dynamic tests on a rotating rig. The whole device weighted 100 kg, comprising the thruster and a cooling system mounted on a beam, supported on a low-friction air bearing. The device reportedly consumed 300 W of power and produced a force of 96.1 mN, a maximum speed of 2 cm/s over 185 cm during testing in October 2006. See this 2007 article by Eureka magazine who covered the story, and this article from Wired the year after, which displays a video where you can see the mammoth.

Interesting thing to note: Shawyer claims the engine starts to accelerate only when the magnetron frequency locks to the resonant frequency of the thruster, following an initial warm up period where it does not move; thus according to him eliminating possible spurious forces.

We'd need some data of tests made with high-Q superconducting cavities. But only Cannae LLC briefly talked about such test results before shutting down their web site. In January 2011, they sent 10.5 watt power pulses of 1047.335 MHz RF power into a resonant superconducting cavity suspended in a liquid helium-filled dewar, detecting a reduction in compressive force on the load cells consistent with a thrust of 8-10 mN. Did someone read their paper published at the 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference in 2014?

Fetta, Guido P. (30 August 2014). Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant. 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. American Institute of Aeronautics and Astronautics. doi:doi: 10.2514/6.2014-3853
« Last Edit: 02/28/2015 07:46 PM by flux_capacitor »

Offline Rodal

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How do you intend to measure the (very tiny) thrust ? Reading back NASA's paper, it seems they had to run the experiment in a lab with complex (and expensive) tools to remove all parasite effects that would interfere with the thrust from the apparatus. Maybe you have access to such equipment ?

- Roger Shawyer achieved 174 mN of thrust at an input power of 450 W in 2010 (he then operated its engine up to 600 W but thrust levels are not known fort that power).
- Chinese NWPU achieved 720 mN @ 2500 W in 2010.
- Eagleworks achieved 116 µN @ 17 W in 2014.

So if you're gonna try an EmDrive at home, you'd better feed it with at least severals hundred of watts of electric power to be able to measure tens to hundreds of millinewtons. Staying below 100 W seems to produce thrusts in the micronewton range, way too low and something only a dedicated lab like Eagleworks can detect with expensive apparatus. At that level you detect any low-frequency vibrations like small seismic events. Indeed you noticed in the paper that Eagleworks used an isolated test rig from the Apollo program era with an extremely sensitive torsion pendulum, and on windy days they were able to detect the waves from the Gulf of Mexico, about 25 miles southeast of JSC… This low-power experiment was intended for a specific purpose: test the EmDrive in a hard vacuum. Only a small device with a compact and light onboard power amplifier could be tested, hence the very low power used compared to previous experiments by Shawyer and the Chinese.

The Chinese pursue a different path: they try to brutally produce the maximum thrust available with cheap but high power magnetrons. This way they cannot eliminate convection current or test their drive in a hard vacuum, but they can show the thrust achieved is too high to be accounted only for trivial reasons. Besides they showed the engine could compete with modern ion thrusters and perhaps one day overtake them.

You can also let the test article rotate. But it's not easy. Shawyer conducted such dynamic tests on a rotating rig. The whole device weighted 100 kg, comprising the thruster and a cooling system mounted on a beam, supported on a low-friction air bearing. The device reportedly consumed 300 W of power and produced a force of 96.1 mN, a maximum speed of 2 cm/s over 185 cm during testing in October 2006. See this 2007 article by Eureka magazine who covered the story, and this article from Wired the year after, which displays a video where you can see the mammoth.

Interesting thing to note: Shawyer claims the engine starts to accelerate only when the magnetron frequency locks to the resonant frequency of the thruster, following an initial warm up period where it does not move; thus according to him eliminating possible spurious forces.

We'd need some data of tests made with high-Q superconducting cavities. But only Cannae LCC briefly talked about such test results before shutting down their web site.
The experimenters may contemplate using the simple Cavendish balance as done by Cavendish in his experiment performed more than 200 years ago (in 1797–98) http://en.wikipedia.org/wiki/Cavendish_experiment.

John Hopkins Applied Physics Laboratory was mentioned in Brady's "Anomalous ..." report as the only University of the three sites being contemplated to replicate the NASA Eagleworks experiment, in the Cavendish apparatus at John Hopkins.

Brady,  March, White, et.al. wrote:  <<The Johns Hopkins University Applied Physics Laboratory has also expressed an interest in performing a Cavendish Balance style test with the IV&V shipset>>

The force involved in twisting the torsion balance by Cavendish was very small:  0.174 microNewtons (certainly small enough to detect the small forces produced by the low power experiments at NASA Eagleworks).



Vibrations in the environment are an issue.  The vibrations produced by nature were also in the environment during Cavendish's time but nowadays we also have vibrations due to heavy trucks on nearby roads, etc.

Another approach is to use the simple hanging pendulum with oil bath damping used by Brito, Marini and Galian (see attached image) in their battery powered MLT-thruster
« Last Edit: 02/28/2015 07:54 PM by Rodal »

Offline Rodal

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....

Interesting thing to note: Shawyer claims the engine starts to accelerate only when the magnetron frequency locks to the resonant frequency of the thruster, following an initial warm up period where it does not move; thus according to him eliminating possible spurious forces.

....

That's very interesting stuff.  Thank you for bringing it up.

Do you have a reference as to where Shawyer  made that interesting claim?

Offline Notsosureofit

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@ RODAL

Still have question about the Shawyer "Demo" cavity w/ 174mN.  What are the current estimates of the cone dimensions, frequency (3.85GHz?), and Q (6000 est?).  When I put in TM02 and 450W, I get 174.8microN, rather than the 174milliN reported.  I would like to recheck those numbers.

Even w/ Q=45000, I need to get X up around (65 Very high mode) to get those numbers.  Is that possible w/ 3.85GHz ??

Thanks
« Last Edit: 02/28/2015 09:32 PM by Notsosureofit »

Offline JPLeRouzic

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So the vacuum did eliminate the thermal hypothesis.
...
5*10-6 Torr is hardly a vacuum good enough to eliminate the thermal hypothesis. That's what you encounter at 1000 km high or so.
Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects.


@Mulletron must have meant "So the vacuum did eliminate the [natural convection] thermal hypothesis" .  He wrote "thermal hypothesis" without the words "natural convection" because he thought that it was obviously understood he was referring to convection in the context he was discussing:  what is the difference between ambient pressure and  5*10-6 Torr.  Obviously this pressure makes a huge difference for natural convection currents, as a trivial calculation can show that 5*10-6 Torr vacuum does eliminate the natural convection hypothesis that was advanced in most media (including Prof. Baez's blog) as the most likely explanation for the measurements.  @Frobnicat, was proposing the thermal convection hypothesis as a possible artifact, and he worked some equations in Thread 1.  I do not recall @Frobnicat objecting to a 5*10-6 Torr vacuum nullifying the hypothesis of natural thermal convection from the EM Drive being able to produce the measured forces. 


Concerning <<Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects>>, yes the Pioneer anomaly was successfully explained by a team of JPL engineers/scientists on the basis of thermal radiation effects (not natural convection thermal effects). 

Thermal radiation, an entirely different (from convection) means of thermal transport, will take place even in a perfect vacuum, as thermal radiation is electromagnetic radiation and therefore does not need a gas or a fluid as a transport medium.  On the other hand natural convection is completely dependent on fluid or gas medium to carry it, and without a fluid or a gas, there cannot be any thermal convection.  Thermal convection involves fluid advection.

Radiative heat transfer is the only form of heat transfer that can take place in a vacuum.  Radiative heat transfer depends on the difference between the fourth power of the temperatures between the radiating surface and the irradiated surface, the surface areas and the emissivities of the radiating and irradiated surfaces and the Stefan–Boltzmann constant .  It may be important for the Pioneer anomaly: an extremely small effect comprising an acceration towards the Sun, of only 8.74×10^(−10) m/s^2, due to asymmetrical radiation of heat from the Radioisotope thermoelectric generators or from the spacecraft electronics reflecting from the back of the spacecraft's dish-like main antenna, causing a recoil like sunlight striking a solar sail.

But in the case of the EM Drive, how much does the temperature difference between radiated and irradiated surfaces have to be to to justify the measured thrust forces ?
You are indeed right about the two thermal effects you mention, and I don't want to be pushed into territories that I don't master and that were not the subject of my initial post.
However I believe (and in writing this, I do something stupid  :)   ) that thermal convection means implicitly that the mean molecular free path is negligible so thermal convection anyway can't exist at all at this pressure.

However that doesn't means we should stop here. At 5*10-6 Torr there are still 5*10^11 molecules per cm3 and mean free path is in the 5m range. I did rule of thumb calcs (that indeed I will never publish 8)), and the thrust is still in the 5-10 µNewton range. My calcs are obviously wrong but indicate that one cannot conclude easily there is absolutely no thermal effect possible at 5*10-6 Torr.   

Offline Rodal

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So the vacuum did eliminate the thermal hypothesis.
...
5*10-6 Torr is hardly a vacuum good enough to eliminate the thermal hypothesis. That's what you encounter at 1000 km high or so.
Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects.


@Mulletron must have meant "So the vacuum did eliminate the [natural convection] thermal hypothesis" .  He wrote "thermal hypothesis" without the words "natural convection" because he thought that it was obviously understood he was referring to convection in the context he was discussing:  what is the difference between ambient pressure and  5*10-6 Torr.  Obviously this pressure makes a huge difference for natural convection currents, as a trivial calculation can show that 5*10-6 Torr vacuum does eliminate the natural convection hypothesis that was advanced in most media (including Prof. Baez's blog) as the most likely explanation for the measurements.  @Frobnicat, was proposing the thermal convection hypothesis as a possible artifact, and he worked some equations in Thread 1.  I do not recall @Frobnicat objecting to a 5*10-6 Torr vacuum nullifying the hypothesis of natural thermal convection from the EM Drive being able to produce the measured forces. 


Concerning <<Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects>>, yes the Pioneer anomaly was successfully explained by a team of JPL engineers/scientists on the basis of thermal radiation effects (not natural convection thermal effects). 

Thermal radiation, an entirely different (from convection) means of thermal transport, will take place even in a perfect vacuum, as thermal radiation is electromagnetic radiation and therefore does not need a gas or a fluid as a transport medium.  On the other hand natural convection is completely dependent on fluid or gas medium to carry it, and without a fluid or a gas, there cannot be any thermal convection.  Thermal convection involves fluid advection.

Radiative heat transfer is the only form of heat transfer that can take place in a vacuum.  Radiative heat transfer depends on the difference between the fourth power of the temperatures between the radiating surface and the irradiated surface, the surface areas and the emissivities of the radiating and irradiated surfaces and the Stefan–Boltzmann constant .  It may be important for the Pioneer anomaly: an extremely small effect comprising an acceration towards the Sun, of only 8.74×10^(−10) m/s^2, due to asymmetrical radiation of heat from the Radioisotope thermoelectric generators or from the spacecraft electronics reflecting from the back of the spacecraft's dish-like main antenna, causing a recoil like sunlight striking a solar sail.

But in the case of the EM Drive, how much does the temperature difference between radiated and irradiated surfaces have to be to to justify the measured thrust forces ?
You are indeed right about the two thermal effects you mention, and I don't want to be pushed into territories that I don't master and that were not the subject of my initial post.
However I believe (and in writing this, I do something stupid  :)   ) that thermal convection means implicitly that the mean molecular free path is negligible so thermal convection anyway can't exist at all at this pressure.

However that doesn't means we should stop here. At 5*10-6 Torr there are still 5*10^11 molecules per cm3 and mean free path is in the 5m range. I did rule of thumb calcs (that indeed I will never publish 8)), and the thrust is still in the 5-10 µNewton range. My calcs are obviously wrong but indicate that one cannot conclude easily there is absolutely no thermal effect possible at 5*10-6 Torr.   
For a third opinion on this matter, it will be interesting to hear comments from @frobnicat (who is also from France  :)  ?), using Frobnicat's thermal convection calculations (discussed in Thread 1) using an atmosphere at  5*10-6 Torr .

If we convert the Torr units used by Paul March to "standard atmosphere" units (we live under 1 atmospheric pressure), the vacuum condition tested by Paul March was:

6.6*10^(-9) atmosphere = 0.0000000066 atmosphere

Offline frobnicat

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So the vacuum did eliminate the thermal hypothesis.
...
5*10-6 Torr is hardly a vacuum good enough to eliminate the thermal hypothesis. That's what you encounter at 1000 km high or so.
Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects.


@Mulletron must have meant "So the vacuum did eliminate the [natural convection] thermal hypothesis" .  He wrote "thermal hypothesis" without the words "natural convection" because he thought that it was obviously understood he was referring to convection in the context he was discussing:  what is the difference between ambient pressure and  5*10-6 Torr.  Obviously this pressure makes a huge difference for natural convection currents, as a trivial calculation can show that 5*10-6 Torr vacuum does eliminate the natural convection hypothesis that was advanced in most media (including Prof. Baez's blog) as the most likely explanation for the measurements.  @Frobnicat, was proposing the thermal convection hypothesis as a possible artifact, and he worked some equations in Thread 1.  I do not recall @Frobnicat objecting to a 5*10-6 Torr vacuum nullifying the hypothesis of natural thermal convection from the EM Drive being able to produce the measured forces. 
...

My specific proposition at the time was a pressure difference build-up between inside cavity and outside, enough to "jet" supposedly warmed air through small apertures of the cavity. I recall having said about 5 month ago I would give a definite answer within 2 month (so much for my credibility with deadlines). This specific "warm jet" hypothesis would have been easily nullified even by a very more modest rough vacuum level of a few Torr. So this specific hypothesis is now ruled out, and I'm glad the experimental progress at Eaglworks outpaced my episodic armchair scientist investment on that matter  :D

For anything pressure related (even complex anisotropic molecular flow like in a Crookes radiometer effect) a characteristic value would be an extreme case of a completely asymmetric pressure difference around 5e-6 Torr = 6.65e-4 Pa on a surface of 11'' diameter = 6.13e-2 m˛ (roughly, cross section of the frustum) that yields about 41µN. Unfortunately still in the ballpark of the signal... so maybe hardcore sceptics could still require 2 orders of magnitude better vacuum, just to be sure... (edit : I see JPLeRouzic reach similar conclusion)

Anyway, it's clear that it becomes difficult to find remaining thermo-aerodynamic effects that would need better than 5e-6 Torr to be ruled out : this is good enough to put possible asymmetric gas flow effects much below the observed signal.

Quote

Concerning <<Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects>>, yes the Pioneer anomaly was successfully explained by a team of JPL engineers/scientists on the basis of thermal radiation effects (not natural convection thermal effects). 

Thermal radiation, an entirely different (from convection) means of thermal transport, will take place even in a perfect vacuum, as thermal radiation is electromagnetic radiation and therefore does not need a gas or a fluid as a transport medium.  On the other hand natural convection is completely dependent on fluid or gas medium to carry it, and without a fluid or a gas, there cannot be any thermal convection.  Thermal convection involves fluid advection.

Radiative heat transfer is the only form of heat transfer that can take place in a vacuum.  Radiative heat transfer depends on the difference between the fourth power of the temperatures between the radiating surface and the irradiated surface, the surface areas and the emissivities of the radiating and irradiated surfaces and the Stefan–Boltzmann constant .  It may be important for the Pioneer anomaly: an extremely small effect comprising an acceration towards the Sun, of only 8.74×10^(−10) m/s^2, due to asymmetrical radiation of heat from the Radioisotope thermoelectric generators or from the spacecraft electronics reflecting from the back of the spacecraft's dish-like main antenna, causing a recoil like sunlight striking a solar sail.

But in the case of the EM Drive, how much does the temperature difference between radiated and irradiated surfaces have to be to to justify the measured thrust forces ?

Very clear.
For the last question, I would be tempted to say : temperatures needing 300 times the actual operating power of the system, since the force/power ratios are ~300 times better than a photon rocket.

Unless the space between the frustum and the vacuum chamber's walls could amplify the effect by bouncing hotter IR photons around a few times and make high temperature, high radiation pressure "traps". IR photons are emitted around all the time, but at thermal equilibrium those radiative pressures have equal contribution on all side of an object in the bath. Anyone knows the typical reflectivity of more or less polished metals in thermal IR ? That would put an upper bound on the "boost" factor compared to the photon rocket equivalent thrust, likely much below 300.

Offline Rodal

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So the vacuum did eliminate the thermal hypothesis.
...
5*10-6 Torr is hardly a vacuum good enough to eliminate the thermal hypothesis. That's what you encounter at 1000 km high or so.
Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects.


@Mulletron must have meant "So the vacuum did eliminate the [natural convection] thermal hypothesis" .  He wrote "thermal hypothesis" without the words "natural convection" because he thought that it was obviously understood he was referring to convection in the context he was discussing:  what is the difference between ambient pressure and  5*10-6 Torr.  Obviously this pressure makes a huge difference for natural convection currents, as a trivial calculation can show that 5*10-6 Torr vacuum does eliminate the natural convection hypothesis that was advanced in most media (including Prof. Baez's blog) as the most likely explanation for the measurements.  @Frobnicat, was proposing the thermal convection hypothesis as a possible artifact, and he worked some equations in Thread 1.  I do not recall @Frobnicat objecting to a 5*10-6 Torr vacuum nullifying the hypothesis of natural thermal convection from the EM Drive being able to produce the measured forces. 
...

My specific proposition at the time was a pressure difference build-up between inside cavity and outside, enough to "jet" supposedly warmed air through small apertures of the cavity. I recall having said about 5 month ago I would give a definite answer within 2 month (so much for my credibility with deadlines). This specific "warm jet" hypothesis would have been easily nullified even by a very more modest rough vacuum level of a few Torr. So this specific hypothesis is now ruled out, and I'm glad the experimental progress at Eaglworks outpaced my episodic armchair scientist investment on that matter  :D

For anything pressure related (even complex anisotropic molecular flow like in a Crookes radiometer effect) a characteristic value would be an extreme case of a completely asymmetric pressure difference around 5e-6 Torr = 6.65e-4 Pa on a surface of 11'' diameter = 6.13e-2 m˛ (roughly, cross section of the frustum) that yields about 41µN. Unfortunately still in the ballpark of the signal... so maybe hardcore sceptics could still require 2 orders of magnitude better vacuum, just to be sure... (edit : I see JPLeRouzic reach similar conclusion)

Anyway, it's clear that it becomes difficult to find remaining thermo-aerodynamic effects that would need better than 5e-6 Torr to be ruled out : this is good enough to put possible asymmetric gas flow effects much below the observed signal.

Quote

Concerning <<Pioneer lives in a vacuum *one million* times better that 5*10-6 Torr and there are still thermal effects>>, yes the Pioneer anomaly was successfully explained by a team of JPL engineers/scientists on the basis of thermal radiation effects (not natural convection thermal effects). 

Thermal radiation, an entirely different (from convection) means of thermal transport, will take place even in a perfect vacuum, as thermal radiation is electromagnetic radiation and therefore does not need a gas or a fluid as a transport medium.  On the other hand natural convection is completely dependent on fluid or gas medium to carry it, and without a fluid or a gas, there cannot be any thermal convection.  Thermal convection involves fluid advection.

Radiative heat transfer is the only form of heat transfer that can take place in a vacuum.  Radiative heat transfer depends on the difference between the fourth power of the temperatures between the radiating surface and the irradiated surface, the surface areas and the emissivities of the radiating and irradiated surfaces and the Stefan–Boltzmann constant .  It may be important for the Pioneer anomaly: an extremely small effect comprising an acceration towards the Sun, of only 8.74×10^(−10) m/s^2, due to asymmetrical radiation of heat from the Radioisotope thermoelectric generators or from the spacecraft electronics reflecting from the back of the spacecraft's dish-like main antenna, causing a recoil like sunlight striking a solar sail.

But in the case of the EM Drive, how much does the temperature difference between radiated and irradiated surfaces have to be to to justify the measured thrust forces ?

Very clear.
For the last question, I would be tempted to say : temperatures needing 300 times the actual operating power of the system, since the force/power ratios are ~300 times better than a photon rocket.

Unless the space between the frustum and the vacuum chamber's walls could amplify the effect by bouncing hotter IR photons around a few times and make high temperature, high radiation pressure "traps". IR photons are emitted around all the time, but at thermal equilibrium those radiative pressures have equal contribution on all side of an object in the bath. Anyone knows the typical reflectivity of more or less polished metals in thermal IR ? That would put an upper bound on the "boost" factor compared to the photon rocket equivalent thrust, likely much below 300.
I agree.

The comments from JPLeRouzic  are well taken. @frobnicat's comments above are well stated.

And this is predicated on the interior of the cavity being at the same pressure as the exterior, as previously discussed with and by Paul March.
« Last Edit: 02/28/2015 10:10 PM by Rodal »

Offline Rodal

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@ RODAL

Still have question about the Shawyer "Demo" cavity w/ 174mN.  What are the current estimates of the cone dimensions, frequency (3.85GHz?), and Q (6000 est?).  When I put in TM02 and 450W, I get 174.8microN, rather than the 174milliN reported.  I would like to recheck those numbers.

Even w/ Q=45000, I need to get X up around (65 Very high mode) to get those numbers.  Is that possible w/ 3.85GHz ??

Thanks

Concerning dimensions for Shawyer's flight thruster, these are the latest estimates I recall:

Big diameter is 265 mm
Small diameter is 189 mm
Height is 164 mm.

From:  http://forum.nasaspaceflight.com/index.php?topic=36313.msg1336809#msg1336809 and http://forum.nasaspaceflight.com/index.php?topic=36313.msg1336754#msg1336754

Shawyer's Flight Thruster development programme. A 3.85GHz thruster weighing 2.92 Kg,

Mean specific thrust = 326mN/kW  (Tests were carried out over an input power range of 150W to 450W.)

At 450W, this thrust/power mean gives a thrust of 146.7 mN  instead of the 174milliN you report for the "Demo".  However, the plot on  http://emdrive.com/flightprogramme.html gives about 170 milliNewton, as you report for the "Demo". I do not see any Q reported on these tests.

This is the only reference I have for data for the Flight Thruster: http://emdrive.com/flightprogramme.html



Concerning Shawyer's Experimental

bigDiameter = 16  centimeter;
smallDiameter = 12.7546  centimeter;
length = 15.6  centimeter;



Concerning Shawyer's Demo

cavityLength = 0.345;
bigDiameter = 0.28;
smallDiameter = 0.128853 cm;




Concerning the data for the Demo and for the Experimental tests of Shawyer, they are in this report: http://www.emdrive.com/IAC-08-C4-4-7.pdf

For the Demo Shawyer states  (notice a number of important differences with the numbers you quoted, including frequency.  Please consider whether you are referring to another test by Shawyer, perhaps to the flight thruster, instead of the Demo):

<<The engine was built to operate at 2.45 GHz, with a design factor of 0.844 and has a measured Q of 45,000 for an overall diameter of 280 mm. The microwave source is a water cooled magnetron with a variable output power up to a maximum of 1.2 kW>>

<<Fig 7 gives test results for 3 Vertical Thrust test runs under the same input and tuner conditions but for thrust vectors in the Up, Down and Horizontal directions. This clearly illustrates the loss of measured weight for the Up vector, the increase in measured weight for the Down vector, and a mean weight change close to zero, for the horizontal vector. These early comparative tests yielded specific thrusts around 80mN/kW.>>

<<Fig 8 shows the results for a test run with the engine on the balance and then with it suspended above the balance. This illustrates the thrust measurements were not subject to EMC effects. Specific thrust for this test was 214mN/kW.>>

<<Fig 10 gives the result of a typical test run, where the Demonstrator Engine produced a thrust of 10.4 gm against a calibrated friction torque of 7.1 gm. Input power was 421W, giving a specific thrust of 243 mN/kW.
The frequency offset curve shows that initial magnetron thermal drift ends with frequency lock. At this point, 130 secs into the test run, the velocity data shows the start of acceleration under power. The prior thermal drift period, with no acceleration, shows that the thrust is not a result of spurious thermal effects. When the power is turned off, at 210 secs, there is a coast period as the slosh effects of 5kg of coolant maintain a reduced acceleration. This is followed by the deceleration due to the friction torque. A maximum velocity of 2cm/s was achieved and a total distance of 185cm was “flown”. The direction of acceleration was opposite to the direction of thrust, thus conclusively proving that the engine obeys Newton’s laws, and that although no reaction mass is ejected, the engine is not a reactionless machine. An  electrical reaction occurs between the EM wave and the reflector surfaces of the resonator, resulting in an input impedance change with acceleration. This is seen in the
power curve in fig 10.>>
« Last Edit: 02/28/2015 11:02 PM by Rodal »

Offline flux_capacitor

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....

Interesting thing to note: Shawyer claims the engine starts to accelerate only when the magnetron frequency locks to the resonant frequency of the thruster, following an initial warm up period where it does not move; thus according to him eliminating possible spurious forces.

....

That's very interesting stuff.  Thank you for bringing it up.

Do you have a reference as to where Shawyer  made that interesting claim?

Yes, it is in the same 2008 paper you have just cited in the message above this one, entitled "MICROWAVE PROPULSION – PROGRESS IN THE EMDRIVE PROGRAMME":
http://www.emdrive.com/IAC-08-C4-4-7.pdf
Where Shawyer noted:
Quote
The frequency offset curve shows that initial magnetron thermal drift ends with frequency lock. At this point, 130 secs into the test run, the velocity data shows the start of acceleration under power. The prior thermal drift period, with no acceleration, shows that the thrust is not a result of spurious thermal effects. When the power is turned off, at 210 secs, there is a coast period as the slosh effects of 5kg of coolant maintain a reduced acceleration. This is followed by the deceleration due to the friction torque. A maximum velocity of 2cm/s was achieved and a total distance of 185cm was "flown".

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