Following on what jknuble said about the multipactor-like effect as a possible cause of thrust. http://en.wikipedia.org/wiki/Multipactor_effect I can't help but wonder about what's going on with the copper surface of the frustum. A quick back of the envelope (well, python) calculation shows that there's certainly enough energy in these devices to somehow atomize a small amount of copper , and propel them with enough momentum to produce a small amount of thrust.
For example, a 30 watt emdrive where 0.001% of the energy went towards atomization and 1% went toward addtional momentum of the particles... You'd have a device with 91uN thrust, propelling 1.4ng of copper a second at 65500m/s.
I can think of 3 ways to debunk this. 1) perhaps that amount of particles going that fast would be noticeable with the naked eye, so this isn't really a valid explanation. 2) stick a detector behind the thruster (are they ionized?). 3) SEM of the surface compared to scraps from the same batch of copper not used in the thrustum.
Just how would we get a net-thrust from a closed cavity with atomization. Even if atoms are being ioniozed inside the cavity I don't see how that could result in a net thrust. Atomization results in immediate thrust but then that creates impact on the other side of the cavity canceling out the propulsion.
I'm talking about signs of atomization on the *outside* surface of the frustum. Although it would probably be happening in the inside as well. The copper atoms would be the propellent. I'm not sure what the mechanism would be, but it's obviously more than a thermal effect, and the whole reversal in phase/thrust would be difficult to explain. It seems more simple than QV or relativity models, but it's still probably interesting physics.
It might also explain the interferometer results.
Hi Everyone,
Just checking in and reading through some comments. Thanks for taking a look at the potential forces involved, rgreen. I believe a force from atomized particles on the interior could have similar - or stronger - effect than being generated on the exterior even if your design is properly vented in vacuum. Especially if the cavity was not designed to be hermetic but is not intentionally vented. Think of a balloon with a pin-hole in it. I did some searching and couldn't find the word "hermetic" or "vented" in the paper or discussions but perhaps the design is vented. If it is designed to be hermetic I would suggest publishing the results of a fine and gross leak test as a hermetic design of this size with braised glass seals for the launch is non-trivial. With a small leak you could have built a simple thruster. The sensitivity of that leak test would need to be appropriate to catch a particle stream that equates to millionths-of-a-pound (more tangible units than "micronewtons" to me) of thrust. This effect could occur in our out of vacuum. This is all speculation and hand-waving though as I don't know all the details of your assembly. While I can't say the exact mechanism that would cause a force to occur, I think it is possible this force is present (sound familiar?

).
Regardless, putting on my "NASA Independent Reviewer" hat, I would say that if you are claiming to have developed a technology which can provide propulsion without a propellant, you have a burden of proof to show that you are not self-generating your propellant due to RF energy interacting with the materials in your setup. These materials could include your metals, coatings, adhesives, dielectrics and / or contaminants. I don't believe there is sufficient evidence from the test points over a range of power levels and in and out of vacuum and across test teams (US, China, Britain) to confirm or refute this as I can imagine situations where particle generating effects would occur in any case due to out-gassing, breakdown, corona, multipaction etc. I am not involved in your effort at all so please forgive my intrusion but from an RF engineering perspective it would be great to see a paragraph in a paper someday explaining how you tested for these effects and can now dismiss them and that you havn't inadvertently built a conventional thruster or ion drive. I saw an earlier post suggesting a wiki be developed which would include potential sources of error and this topic could be filed there.
I believe a good test would involve at least following (again, my apologies if these were done in part or seem obvious.. I am also repeating myself a bit here from earlier posts):
1 - Add sufficient vent holes to the RF cavity. Ensure the hole diameter is small enough such that their wave-guide effects do not effect the S11 of the system in the range you're operating in. It seems you do have an ability to do 3D e-mag simulations but here is a tool you can use to verify the venting does not have a significant electrical impact:
http://multipactor.esa.int/features.html. Unless you have specifically designed the system to be hermetic with glass seals etc, it will slowly leak and confuse the test and possibly be the source of thrust. Hopefully you are not currently relying on your antenna launch or fasteners on the cavity caps for venting. Testing under vacuum is actually the best way to resolve this issue and is the "relevant space environment" (i.e. high TRL!) so hermetic designs should be avoided as this helps your case anyways. The proposed physics don't require a gas to be present, correct? To be clear, whether or not you are currently vented does not confirm or refute anything as I can envision scenarios where a force would be generated even with a properly vented design in normal atmosphere from the momentum imparted by the particles at the focused atomization point (millionths-of-a-pound!)... so this is just a first step.
2 - Ensure you perform an un-powered elevated temperature bake-out of the DUT and support electronics at 50 to 60C for least 24 hours under vacuum. This is generally what we do for RF space-flight hardware as that is what is required to get most of the typical volatiles out of a system. It looks like this was done for the chamber but the DUT does not appear to have been heated. This needs to include any support electronics - in fact, move all but the bare minimum of electronics outside the chamber. Completion of most out-gassing should be observed not with your vacuum pump monitor but with a TQCM in real-time (
http://en.wikipedia.org/wiki/Quartz_crystal_microbalance). Note- this bake-out is a pretty crucial step to eliminate the possibility of simple out-gassing being the culprit for this phenomenon. Out-gassing can be a non-linear behavior in some materials. Some materials out-gas at a rate proportional to their temperature. Others will not begin out-gassing until they reach a certain temperature. So the experimenter should perform an un-powered bake-out over the range of temperatures the *powered* system should expect to see. So if you are dissipating 2.6W in your cavity a thermal analysis should be done to see what temperature the system (especially the launch) would get to in vacuum. Alternatively just instrument it properly and run a test first. A bake-out will need to be properly done prior to every test as re-exposure to atmosphere will re-coat the DUT with contaminants and your dielectric will absorb moisture. A mistake we made on the Aquarius mission (
http://aquarius.nasa.gov/) was not performing a high temperature bake-out with our heaters once we reached orbit. Consequently it took weeks for the system to stabilize as the dielectrics out-gassed moisture and we could observe the dielectric constant of RF boards drifting. In short, ensure the un-powered temperatures reach and exceed the temperatures caused by RF heating when operational at the test temperature.
[General note on the 2.6W case as it is often used for an argument against the causes I have listed: Some have noted the 2.6W test is "low" but that is a huge amount of power for parts to handle in my field (RF radiometry). For example, consider that few of the passive parts sold by these folks can handle more than a watt or 10s of watts unless they are specially engineered for high power applications:
http://www.minicircuits.com/ Consider what is actually occuring in the part when you reach the maximum power level and could that effect generate enough particles to create millionths-of-a-pound of pressure. Also, in many components the limiting factor is the launch design. Returning to your test setup, your PTFE insert will certainly heat and out-gas due due to a portion of the 2.6W of RF power being dissipated within it. I note the slow time-constant on the plot in Figure 22 looks an awful lot like what you would see from a thermal effect, particularly as thrust slowly decays after RF power is removed:
http://arc.aiaa.org/doi/pdf/10.2514/6.2014-4029. Also I interpret the setup as 2.6W being dissipated in chamber but with 28W incident from the power amps with the related electric field levels of 28W in your system. This is my understanding based on this statement in Part B of
http://arc.aiaa.org/doi/pdf/10.2514/6.2014-4029: "
In this test configuration, the VNA system indicated a quality factor of ~7320, and the difference of power forward and power reflected as reported by the power meters was indicated to be ~16.92 watts as a result of manual tuning to maximize the power difference. " So for purposes of thermal effects, 2.6W is correct. But for breakdown effects, the electric field strength associated with 28W is what should be considered, simulated and evaluated against breakdown.]
3 - Once the system is stabilized, I would turn on the RF power transmitting into an RF coaxial short rather than a load, perhaps with an RF switch. A full reflection which is a worst-case in your system could cause issues on your source and induce some out-gassing or breakdown from that device. Ensure the TQCM does not detect anything. This will let you know if your setup would cause a false-negative for the test I'm proposing. Generally, ensure you have brought on an experienced materials or contamination engineer to set this test up for you. Also this would serve as further proof there are not a conducted or radiated interference issue. The paper notes the DC currents from the power amps do effect the measurement to a degree so this case is more similar to what the amps are actually driving just to be thorough.
4 - Turn on your system in the normal test setup and observe the TQCM. If particles are detected you may have found the culprit as these may be the result of out-gassing, breakdown, corona, multipaction, etc. These effects all generate particles and correspond to different power levels and environments. This step can be tricky but I've seen it work well when experienced people are involved. When you have pulled a vacuum, small particle generation detection is more reliant on Brownian motion etc. to cause particles to exit the vent holes and get to the detector so some care is required here. As I mentioned in an earlier comment this was the method used to verify that multipaction was occuring within the SMAP diplexers and not a purely reactive effect.
5- Allow the system to run for at least a week to ensure the force does not dissipate or change due to a propellant being expended. Also, if possible, increase the sampling rate of your force sensor to be faster than what one would see from thermal effects. I'm not at all familiar with the proposed physics to explain the phenomenon but generally a purely RF cause should result in "instantaneous" force. Faster than milliseconds should be enough to discount thermal effects although not all the sources of error I have mentioned are thermal.
6 - (Mentioned this previously) - Open the cavity and have someone experienced inspect the materials for any evidence of breakdown. A detailed inspection and cleaning should be done before the unit is sealed if that is possible.
So hopefully some of this is helpful. Someone else may be able to devise a more compelling test for the hypothesis. In summary, there are a variety of particle generating effects of high RF power including out-gassing, corona breakdown, multipaction, plasmas, etc. Each can occur at different power levels, some will occur in vacuum, some not. It is possible each of the teams is seeing one or more of these effects depending on these variables during any given test. The above statements are general and also apply to the tests done by the Chinese and British teams and any future test. So while "multipaction" may not be the current culprit with the setup at 28W it could be as testing is done at higher power levels. I have focused much of the above discussion on the small 28W case in the referenced paper but KW of RF energy are known to cause somewhat violent events including (but not always) magic smoke and burned components. So generating a newton of force during these events seems conceivable.
I dug around online for resources related to high power breakdown at RF frequencies and couldn't find much. Here are a few things but these may a bit too basic.
http://en.wikipedia.org/wiki/Electrical_breakdownhttp://www.microwaves101.com/encyclopedias/power-handlingHelpful tool:
http://multipactor.esa.int/I hope this post wasn't too rambling or too full of misconceptions regarding the tests you have performed. I don't envy you folks trying to make progress on this complex issue via a public internet forum. Good luck, and again, I hope I'm wrong!
-Joseph Knuble,
NASA GSFC Code 555
Microwave Instrument Technology Branch
Final note for any students here who are curious about RF: This is far below the power levels I believe you have operated at but for future consideration at the 100W to KW level note the acoustic (i.e. pressure) effects of this demonstration which uses a 2.4GHz magnetron in a closed cavity with a contaminant:
Depending on the dynamics involved, teams which have tested at high power could be seeing the effects of a similar unstable vibration (think of your vibrating cell-phone skittering across the table.)