Author Topic: Propellantless Field Propulsion and application  (Read 666018 times)

Offline douglas100

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Re: Propellantless Field Propulsion and application
« Reply #1740 on: 12/03/2012 03:30 PM »
Whose math?

EDIT: Sorry John, I thought that question was directed at me.
« Last Edit: 12/03/2012 03:32 PM by douglas100 »
Douglas Clark

Online Elmar Moelzer

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Re: Propellantless Field Propulsion and application
« Reply #1741 on: 12/03/2012 03:30 PM »
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.

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1742 on: 12/03/2012 04:39 PM »
Afrocle:  Have you vetted their math, or are you accepting it?

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 Chinese also do not say what the dimensions of their microwave cavity are or how it is shaped. They say that they use "integrals" to shape the walls of the cavity to get a net positive thrust in a particular direction, but they don't give the math for this.

If this thruster is something easy to make (which is possible when I look at the YouTube video), then I would keep these dimensions and the shape of the cavity a trade secret and rapidly bring it to market as a replacement for existing Hall-effect thrusters.

If this is a hoax, then they might be vague on purpose.

I tend to believe that someone (not me) on this forum who understands radiation pressure and microwave cavities can easily and rapidly show us how the magnitude of radiation pressure needed for 720 nN of thrust can be achieved by insering a 2.5-kw and 2.45-Ghz wave into a ~ 6-cm cavity.

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1743 on: 12/03/2012 04:43 PM »
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.

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.

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1744 on: 12/03/2012 05:02 PM »
Quote from Afrocle:

Quote
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.

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.

I agree with you that shaping the force vectors for net positive thrust is a controversial point.

This is why I made the analogy to the use of triangular sails that could sail into the wind over 1,000 years ago, even though the math and principals underlying the shaping and adding of the force vectors from airfoil wings (i.e. the triangular sails) and hydrofoil hulls did not exist until 1,000 years later.

We know that solar sails and laser sails work using radiation pressure today, just like people knew that they could sail with the wind using direct wind pressure on square sails over 4,000 years ago. The hard part is applying the same principals in a much more complex environment adding multiple different force vectors.

I think that someone on this forum could check the math to see if you can get milliNewtons of radiation pressure at a distance under 10-cm from a 2.5-kw 2.45-Ghz source. This will at least let us know that the orders of magnitude of the EMDrive are possible.

I agree that it will be much harder to figure out how you add the trillions of force vectors from photons bouncing off of microwave cavity walls as reflections (i.e. twice the absorption power), as absorptions, or as heat to come up with a net positive thrust moving in a single desired direction. When the Chinese discuss "integrals" within their paper, I assume that they are using a computer to model different shapes and materials within the microwave cavity to achieve their goal. I personally think that net positive thrust should be possible, but I don't know how to design microwave cavities or how to measure radiation pressure levels within cavities.

Online Elmar Moelzer

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Re: Propellantless Field Propulsion and application
« Reply #1745 on: 12/03/2012 05:35 PM »
Quote
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.

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.

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1746 on: 12/03/2012 05:54 PM »
Quote
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.

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.

The photons causing the radiation pressure are moving at the speed of light, so I do not understand how the power source moving with the EMDrive would negatively the direction of the photons.

Having the power source attached to the EMDrive could have a negative effect in that the radiation pressure from the power source sends momentum or force vectors in directions opposite to the intended net positive direction of thrust (versus the sun sending radiation pressure to a solar sail in a line from the sun to the space ship), but I think that this is where the theory behind the shaping and adding of these vectors within the microwave cavity comes into play.

Shaping the direction, number, energy, mass, and magnitude of photons is very different then shaping how air comes from a propellor to create thrust (and drag). 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.

Online Elmar Moelzer

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Re: Propellantless Field Propulsion and application
« Reply #1747 on: 12/03/2012 07:32 PM »
Quote
Having the power source attached to the EMDrive could have a negative effect

that is what I have heard

Offline 93143

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Re: Propellantless Field Propulsion and application
« Reply #1748 on: 12/03/2012 08:07 PM »
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.

Quote
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.

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.
« Last Edit: 12/03/2012 08:19 PM by 93143 »

Online Elmar Moelzer

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Re: Propellantless Field Propulsion and application
« Reply #1749 on: 12/03/2012 08:10 PM »
Quote
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.
You explained it better than I could have, thanks!

Offline sfuerst

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Re: Propellantless Field Propulsion and application
« Reply #1750 on: 12/03/2012 08:26 PM »

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.

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.

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1751 on: 12/03/2012 10:11 PM »
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.

Quote
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.

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.

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).

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?

Thank you.

Online Elmar Moelzer

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Re: Propellantless Field Propulsion and application
« Reply #1752 on: 12/03/2012 10:22 PM »
Quote
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).
That is not just photons though, right?

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1753 on: 12/03/2012 10:23 PM »

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.

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?

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1754 on: 12/03/2012 10:26 PM »
Quote
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).
That is not just photons though, right?

Not right.

That is just radiation pressure from photons which should not be confused with the seperate solar wind of charged particles.

Offline 93143

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Re: Propellantless Field Propulsion and application
« Reply #1755 on: 12/03/2012 10:32 PM »
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

This 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 = 8.34

Quote
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?

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.

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?

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.
« Last Edit: 12/03/2012 10:35 PM by 93143 »

Online Elmar Moelzer

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Re: Propellantless Field Propulsion and application
« Reply #1756 on: 12/03/2012 10:35 PM »
Quote
Not right.

That is just radiation pressure from photons which should not be confused with the seperate solar wind of charged particles.
Ok, thanks for the clarification.

Online QuantumG

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Re: Propellantless Field Propulsion and application
« Reply #1757 on: 12/03/2012 10:36 PM »
The Isp is theoretically infinite for these propellantless thrusters

No it isn't.

Jeff Bezos has billions to spend on rockets and can go at whatever pace he likes! Wow! What pace is he going at? Well... have you heard of Zeno's paradox?

Offline Afrocle

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Re: Propellantless Field Propulsion and application
« Reply #1758 on: 12/03/2012 10:43 PM »
The Isp is theoretically infinite for these propellantless thrusters

No it isn't.



Thank you.

What is the Isp and how do you calculate it for a photon thruster using radiation pressure?

Offline 93143

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Re: Propellantless Field Propulsion and application
« Reply #1759 on: 12/03/2012 10:50 PM »
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 NĚs of impulse you get from your drive.

In other words, the specific impulse is 299792458 NĚs/kg, or 30570323 seconds.

If you use solar power, on the other hand, the Isp really is infinite...
« Last Edit: 12/03/2012 10:54 PM by 93143 »

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