QuoteMaybe I do not understand your statement, but isn't that obvious?The EMDrive will only have thrust when there is external power being supplied to it from solar panels or a nuclear reactor or some other source of electricity. No, I meant a powersource that is not in the same reference frame as the EM drive (e.g. attached to it). From what I understand all current experiments were run with the power supply not beig moved with the drive itself.
Maybe I do not understand your statement, but isn't that obvious?The EMDrive will only have thrust when there is external power being supplied to it from solar panels or a nuclear reactor or some other source of electricity.
Quote from: Afrocle on 12/03/2012 10:11 pmHow did you calculate your 8.3 x 10-6 Newtons of thrust from a 2.5-kw power source? It is already established that a solar sail achieves a larger 9.15 x 10-6 Newtons of thrust from a smaller 1.37-kw power source (i.e. the sun at 1 AU).Quote from: Afrocle on 12/03/2012 05:54 pmphotons reflect off surfaces at twice the radiation pressure that they are absorbed by surfacesThis is because the incoming and outgoing momenta are equal and opposite. With absorption - or radiation - you only have one or the other.(9.14/2)*2.5/1.37 = 8.34QuoteWhat or where is this "equal and opposite force somewhere else in the power system" that balances the other EMDrive forces and prevents the EMDrive from working?It's not a question of "preventing the EMDrive from working". Conservation of momentum must be satisfied. If the source of the thrust is ordinary electromagnetism (which I'm not claiming), then the reaction is most likely electromagnetic, and while it could be interacting with Earth's magnetic field or an unrelated piece of lab equipment someone forgot to turn off, another possible explanation is that the circuit is producing some sort of inductive effect, or perhaps a charge separation - some sort of electromagnetic effect internal to the integrated test setup, which would naturally sum to zero over the whole apparatus.I don't know what the source of the thrust is. We don't have enough information yet.Quote from: Afrocle on 12/03/2012 10:23 pmWhat are you comparing this "too small" thrust to? An ion drive engine at 5,000-sec Isp would have 10 times less thrust for the same power input as the EMDrive, so what ion drive are you basing your comment on?Yes, but we don't know the EM-Drive works yet. He's comparing the ion drive to a conventional photon drive, which has a power-to-thrust ratio of 299792458 W/N.
How did you calculate your 8.3 x 10-6 Newtons of thrust from a 2.5-kw power source? It is already established that a solar sail achieves a larger 9.15 x 10-6 Newtons of thrust from a smaller 1.37-kw power source (i.e. the sun at 1 AU).
photons reflect off surfaces at twice the radiation pressure that they are absorbed by surfaces
What or where is this "equal and opposite force somewhere else in the power system" that balances the other EMDrive forces and prevents the EMDrive from working?
What are you comparing this "too small" thrust to? An ion drive engine at 5,000-sec Isp would have 10 times less thrust for the same power input as the EMDrive, so what ion drive are you basing your comment on?
Quote from: Elmar Moelzer on 12/03/2012 05:35 pmQuoteMaybe I do not understand your statement, but isn't that obvious?The EMDrive will only have thrust when there is external power being supplied to it from solar panels or a nuclear reactor or some other source of electricity. No, I meant a powersource that is not in the same reference frame as the EM drive (e.g. attached to it). From what I understand all current experiments were run with the power supply not beig moved with the drive itself.IIUC, the EM Drive is claimed to reduce in efficiency as it speeds up. Don't understand how that is compatible with Relativity.cheers, Martin
Power-to-thrust is 299792458 W/N, as I mentioned above. This means that if you generate the power internally, you need to convert (assuming 100% efficiency) 3.33564095e-9 kg into energy and expel it for every N·s of impulse you get from your drive.In other words, the specific impulse is 299792458 N·s/kg, or 30570323 seconds.If you use solar power, on the other hand, the Isp really is infinite...
isp is just a peculiar way of measuring thrust per unit of energy. Saying isp is infinite, even for an externally powered thruster, gives the wrong impression.
Radiation pressure is a surface effect, not a volume effect.And did you notice that the calculation completely answers your question? It's not how I got my number originally; it just shows that it's consistent with yours.
Quote from: sfuerst on 12/03/2012 08:26 pmQuote from: Afrocle on 12/03/2012 04:39 pmThe Chinese paper gives a direction for how the EMDrive works (i.e. it is like a solar sail working under the understood principles of radiation pressure), but it does not give specific math of how they come to the 720 mN thrust with a 2.5-kw 2.45-Ghz input. If you want thrust from radiation pressure, there are much easier ways of doing it. Just use a light bulb and a parabolic mirror. The isp from such a photon-rocket "thruster" is enormous. However, obviously no one uses such a thing, the reason being that the thrust is too small. It's better to add a small amount of reaction mass and use something like an ion drive.What is the performance in terms of thrust in Newtons versus power input in kw for your easier "light bulb and parabolic mirror" thruster? The Isp is theoretically infinite for these propellantless thrusters so Isp is not the goal for your improvement on the photon-rocket.What are you comparing this "too small" thrust to? An ion drive engine at 5,000-sec Isp would have 10 times less thrust for the same power input as the EMDrive, so what ion drive are you basing your comment on?
Quote from: Afrocle on 12/03/2012 04:39 pmThe Chinese paper gives a direction for how the EMDrive works (i.e. it is like a solar sail working under the understood principles of radiation pressure), but it does not give specific math of how they come to the 720 mN thrust with a 2.5-kw 2.45-Ghz input. If you want thrust from radiation pressure, there are much easier ways of doing it. Just use a light bulb and a parabolic mirror. The isp from such a photon-rocket "thruster" is enormous. However, obviously no one uses such a thing, the reason being that the thrust is too small. It's better to add a small amount of reaction mass and use something like an ion drive.
The Chinese paper gives a direction for how the EMDrive works (i.e. it is like a solar sail working under the understood principles of radiation pressure), but it does not give specific math of how they come to the 720 mN thrust with a 2.5-kw 2.45-Ghz input.
The EMDrive is getting larger thrust than allowed by physics. So... either they are lying, or miss-measuring something.
Quote from: sfuerst on 12/03/2012 11:52 pmThe EMDrive is getting larger thrust than allowed by physics. So... either they are lying, or miss-measuring something.Or the operating principle is something in between the cracks in our current understanding of physics.I do not comment on the likelihood that this is true.
Your question had nothing to do with a resonant cavity. You asked how my value for a flashlight drive was consistent with your value for a solar sail. I pointed out that the 2x difference between reflection and generation explained the discrepancy.This assumes that the radiation is unidirectional (which is pretty realistic in both cases but inconsistent with the scenario described by the Wiki page), and that the solar sail is facing the sun straight on, which gives maximum thrust.Besides, your talk of 1 AU vs. 6 cm seems to imply that you missed the significance of "per unit volume". All that matters is the radiative intensity, and since we already know that, the volume doesn't matter.Kilowatts per square metre are not a volumetric quantity; how far away the radiation came from is entirely irrelevant.
Hoping that something as well understood as basic electromagnetism has applications that break the laws of conservation of momentum and energy
Quote from: sfuerst on 12/04/2012 12:30 amHoping that something as well understood as basic electromagnetism has applications that break the laws of conservation of momentum and energyWho said anything about breaking conservation? M-E doesn't. If the EM-Drive works (which I am not claiming), whatever makes it work can be assumed to also not break conservation unless very good evidence shows up that it does.
I do not remember asking for the value of a flashlight drive.
Quote from: 93143 on 12/03/2012 08:07 pmI do know that the maximum thrust achievable by radiation pressure at 2.5 kW is 8.3 micronewtons.How did you calculate your 8.3 x 10-6 Newtons of thrust from a 2.5-kw power source? It is already established that a solar sail achieves a larger 9.15 x 10-6 Newtons of thrust from a smaller 1.37-kw power source (i.e. the sun at 1 AU).
I do know that the maximum thrust achievable by radiation pressure at 2.5 kW is 8.3 micronewtons.
If you have 1.37-kw applied a meter away from a surface versus 2.5-kw applied 6-cm away from a surface then there should be a significant difference in pressure on that surface.
I don't rule out the possibility that these researchers have constructed a device that defies current understanding of momentum, etc, and that it might actually be practical for some purposes. I just don't have enough information to reproduce it, and there's no good reason for them to have failed to publish that information.What is that information? The exact dimensions of the cavity, the materials used, and the exact frequency of the microwaves. In short: what's the recipe? Spell it out. Neither group has done that and yet both groups are claiming success. How are we supposed to know they're even seeing the same phenomena?
Quote from: QuantumG on 12/04/2012 12:36 amI don't rule out the possibility that these researchers have constructed a device that defies current understanding of momentum, etc, and that it might actually be practical for some purposes. I just don't have enough information to reproduce it, and there's no good reason for them to have failed to publish that information.What is that information? The exact dimensions of the cavity, the materials used, and the exact frequency of the microwaves. In short: what's the recipe? Spell it out. Neither group has done that and yet both groups are claiming success. How are we supposed to know they're even seeing the same phenomena?I am reading a NASA funded paper right now that might have some of the recipe for this type of photon thruster. I am trying to see if it is flaky before posting it.