Afrocle: Have you vetted their math, or are you accepting it?
Some critics of the EM drive say that it will not produce thrust as soon as the power does not come from an external source.
Quote from Afrocle:QuoteIf photons are reflected inside the cavity walls, then they can impart their pressure at twice the absorbtion pressure many times before final photon absorption or scattering, but all of these force vectors must be shaped and added to obtain a net positive thrust in a desired direction.You'll be aware that the part I made bold is controversial. Newtonian mechanics suggests that it is not possible to shape the force vectors within the cavity to produce net thrust in a given direction.On the other hand, John Fornaro has a point: at least we know the solar sail works.
If photons are reflected inside the cavity walls, then they can impart their pressure at twice the absorbtion pressure many times before final photon absorption or scattering, but all of these force vectors must be shaped and added to obtain a net positive thrust in a desired direction.
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.
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.
Having the power source attached to the EMDrive could have a negative effect
I think that the fact that photons reflect off surfaces at twice the radiation pressure that they are absorbed by surfaces gives the engineers of a microwave cavity something to work with.
What's being suggested is that the force is an electrodynamic effect balanced by an equal and opposite force somewhere else in the power system. Attaching the power system to the thruster would thereby eliminate the measured thrust.
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.
What's being suggested is that the force is an electrodynamic effect balanced by an equal and opposite force somewhere else in the power system. Attaching the power system to the thruster would thereby eliminate the measured thrust.I don't know if that's true.I do know that the maximum thrust achievable by radiation pressure at 2.5 kW is 8.3 micronewtons. But then, we're discussing a resonant cavity here; the instantaneous power level is beside the point. (If you wanted single-shot radiation pressure performance, you could just shine a light backwards from your spacecraft.)You cannot get a net thrust by adding the radiation pressure on all sides of the chamber, unless something weird is going on that renders the thruster an open system interacting with [part of] the rest of the universe somehow. Simple vector addition will always sum to zero; it doesn't matter what the shape of the chamber is. This is a geometric law.If this thing works, it will be for some weird reason, probably involving nonlocality and/or zero-point fluctuations or some such. Reportedly, Sonny White's QVF theory predicts thrust from an EM-Drive, but Jim Woodward's M-E theory does not.QuoteI think that the fact that photons reflect off surfaces at twice the radiation pressure that they are absorbed by surfaces gives the engineers of a microwave cavity something to work with.It doesn't. Generating them produces the other half of the reflection pressure.Guys, you are not going to make this thing work by messing with Newtonian mechanics and Euclidean geometry and Maxwellian electromagnetics. You are up against fundamental generally-applicable mathematical truths here.
t 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 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.
Quotet 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).That is not just photons though, right?
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?
Not right.That is just radiation pressure from photons which should not be confused with the seperate solar wind of charged particles.
The Isp is theoretically infinite for these propellantless thrusters
Quote from: Afrocle on 12/03/2012 10:23 pmThe Isp is theoretically infinite for these propellantless thrustersNo it isn't.