Author Topic: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive  (Read 192269 times)

Offline ppnl

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #140 on: 04/30/2015 08:05 PM »
What I'm not following from ppnl's (and other perpetual-motion theorizers') argument is how a constant thrust, sans propellant, results in a perpetual-motion, inventing-energy-from-nowhere scheme. Surely, even with a propellant-based thruster, there exists some threshold V relative to some reference frame, wherein the loss of M from propulsion is completely dominated by the increase in V, since KE = (1/2)M*V2?

Looking at KE, or dKE/dt, seems fallacious to me for that reason. Maybe I just don't understand the math well enough.

It isn't clear to me what you are saying here.

Take a car. It takes four times as much energy to accelerate from 10 mph to 20 mph as it took to accelerate from zero to ten mph. A rocket has the same problem but much worse because it takes its reaction mass with it.


Offline ppnl

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #141 on: 04/30/2015 08:21 PM »
It is not close mindedness to point out that violating conservation of energy and momentum create massive problems for the supposed effect. This is especially true when many of the proponents do not understand that the conservation laws are being violated or understand the consequences of those violations.

You are assuming that conservation of energy or momentum would be violated. This is only true if the device (and its attached spaceship, if any) is a closed system, but the basis of the proposed theories of how it works is that it is NOT a closed system. Instead it is coupled to the quantum vacuum somehow, and the change in momentum of the device could be balanced by an equal but opposite change in the local momentum of the quantum vacuum, which could propagate from virtual particle to virtual particle in a wave-like manner (like a sound wave) until it is transfered to (possibly quite distant) non-virtual matter. Although by then the momentum transfer per unit mass would be so tiny that it would probably be quite undetectable.

I'm not assuming it I'm pointing out that it appears to be violating energy and momentum. You can have it reacting against some quantum vacuum but that does not solve the problem yet. If the thing accelerates constantly you still have conservation of energy problems. If it does not then you have created a preferred frame of reference in violation of relativity.

Now you may find a way around these problems but first you need to understand that these problems exist.

I have thought about a science fiction drive that reacts against the local gravitational gradient. This would not violate energy or momentum. But that isn't a scientific theory. It is a work of fiction. Almost certainly no such device is possible.

The problem with these these cold fusion type claims is it causes us to confuse science and science fiction.

Offline gospacex

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #142 on: 04/30/2015 08:23 PM »
Taking conservation of energy literally or dogmatically, then energy can neither be created nor destroyed, and hence should be Zero in any coordinate at any given instance in time.

The latter does not follow from the former.

Offline gospacex

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #143 on: 04/30/2015 08:34 PM »
I agree, it isn't closed minded to point that out. However it is closed minded if you believe what has been accepted as a LAW of physics can never be disproven or modified.

Do you see anyone here saying such a stupid thing? I don't.

Quote
This theory will not be disproven by logic. It will only be disproven, or proven, by scientific experimentation and examination of emperical evidence. Anyone who thinks it will be proven solely by logical argument of currently known physics IS CLOSED MINDED. You have to experiment according to scientific method protocol and then you have to FOLLOW THE EVIDENCE.

You are not getting what we "the skeptics" are saying.

We are not saying that evidence should be ignored.

We are saying that implications of the device working as claimed are so extraordinary that fantasizing about building spaceships to Alpha Centauri is the last thing we need to do. Doing this *now* just makes one look a bit like an obsessed person.

The thing to do now is to provide extraordinary, compelling evidence. Experiment needs to be redone in a much more clean environment. Eventually, if/when tests in vacuum but on Earth seem to still show the effect, it will need to be redone in space, away from Earth magnetic field, IR radiation etc.

*THEN* the claims will be taken by most scientists very seriously.
« Last Edit: 04/30/2015 08:35 PM by gospacex »

Offline CW

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #144 on: 04/30/2015 08:38 PM »
Taking conservation of energy literally or dogmatically, then energy can neither be created nor destroyed, and hence should be Zero in any coordinate at any given instance in time.

The latter does not follow from the former.

If you want to avoid supernatural influence in shape of gods or other unphysical things that can magically pull any trick they want, it does.
« Last Edit: 04/30/2015 08:46 PM by CW »
Reality is weirder than fiction

Offline indigodarkwolf

What I'm not following from ppnl's (and other perpetual-motion theorizers') argument is how a constant thrust, sans propellant, results in a perpetual-motion, inventing-energy-from-nowhere scheme. Surely, even with a propellant-based thruster, there exists some threshold V relative to some reference frame, wherein the loss of M from propulsion is completely dominated by the increase in V, since KE = (1/2)M*V2?

Looking at KE, or dKE/dt, seems fallacious to me for that reason. Maybe I just don't understand the math well enough.

It isn't clear to me what you are saying here.

Take a car. It takes four times as much energy to accelerate from 10 mph to 20 mph as it took to accelerate from zero to ten mph. A rocket has the same problem but much worse because it takes its reaction mass with it.
A car doesn't contain reaction mass? What about gasoline?

Also, it doesn't take 4x the energy to double a car's velocity. A car has 4x the KE after doubling velocity, but that is not the same thing as saying 4x KE was required to get there.

Not to mention, the energy requirements of accelerating a car include overcoming wind resistance and friction, which resists the forward motion of the car. Maintaining a velocity against these forces is a measure of work, not energy. And since the formula for the force of drag resistance also includes V2, that means that there is 4x as much drag at 20mph as there is at 10mph, and so 4x as much work is required to maintain velocity each time you double velocity. This is still not the same thing as 4x as much energy.

Offline Karlman

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #146 on: 04/30/2015 08:56 PM »
(snip...)
The thing to do now is to provide extraordinary, compelling evidence. Experiment needs to be redone in a much more clean environment. Eventually, if/when tests in vacuum but on Earth seem to still show the effect, it will need to be redone in space, away from Earth magnetic field, IR radiation etc.

*THEN* the claims will be taken by most scientists very seriously.

From the article, it looks like NASA Eagleworks has replicated the results in a vacuum in the lab:
Quote
However, Paul March, an engineer at NASA Eagleworks, recently reported in NASASpaceFlight.comís forum (on a thread now over 500,000 views) that NASA has successfully tested their EM Drive in a hard vacuum Ė the first time any organization has reported such a successful test.

To this end, NASA Eagleworks has now nullified the prevailing hypothesis that thrust measurements were due to thermal convection.

Offline coypu76

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #147 on: 04/30/2015 09:12 PM »
I'm not a scientist or an engineer, just a geek, so I've been reticent to post.  A couple of observations:

1. The blogosphere and various social media seem to have really jumped the shark on the "Warp drive" stuff. 

2.  Thrust in vacuum has been verified - but what was the range of thrust Eagleworks observed with 100W input?  The article says the Chinese saw ~700mN with 2.5KW input.

3.  Is the speculation about "warp drives" and such related to the interesting diffraction pattern that resembles, at least superficially, what one might expect from a warp bubble?  (a lot of other things look like concentric waves, so I think perhaps I'll limit my response to this to, "Hmm.  Interesting."

4.  Suggestions for modest space experiments:  The trunk on SpaceX's Dragon has solar cells that generate up to 5KW.  Seems to me a fairly inexpensive experiment would be to mount an EMDrive in the trunk on a pivoting frame with actuators and a telemetry/control unit.  The trunk could be used to experiment with the EMDrive after the Dragon jettisons it for re-entry. Or a mini-sat with solar cells, batteries, telemetry/control and an EMDrive test unit could easily be stowed in a Falcon 9 second stage or Dragon's trunk for deployment as a secondary mission.  Isn't it feasible that some sort of test article with control/telemetry can be crowdsourced and lofting purchased (or begged) on a mission, riding in an F9 stage 2 or Dragon's trunk?

5.  Has anyone contacted Roger Shawyer for a comment?  I'd be interested to see what he has to say about what seems to be an emerging consensus of vindication for his drive.

Thanks for allowing a mere mortal to add my 2 cents worth of questions and comments.

Offline Cinder

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #148 on: 04/30/2015 09:16 PM »
What's the cheapest EM spacecraft design that should do clearly impossible things?

About $10,000. You could Kickstarter it and get it on the next Dragon flight, ala A3R. Heck, there's cubesats that have flown for less.

This seems about right and is a major reason I'm skeptical. Lab experiments are pointless for convincing anyone. Based on everything reported it should be quite easy to put an EMdrive on a little satellite paid for by Kickstarter and get it a free ride in the trunk of a Dragon. It just has to change it's orbit in a way that according to claims should be easy for First Gen EM drive but also be impossible for any accepted technology. It should be able to keep up orbital maneuvering long after it would be impossible using any known design. This would be transparent and open to the world. Cue Nobel prize, whatever funding they want, Heinlein prize, eternal glory. What's stopping this?
Insufficient characterization?
« Last Edit: 04/30/2015 09:17 PM by Cinder »
The pork must flow.

Offline ppnl

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #149 on: 04/30/2015 09:21 PM »
(snip...)
The thing to do now is to provide extraordinary, compelling evidence. Experiment needs to be redone in a much more clean environment. Eventually, if/when tests in vacuum but on Earth seem to still show the effect, it will need to be redone in space, away from Earth magnetic field, IR radiation etc.

*THEN* the claims will be taken by most scientists very seriously.

From the article, it looks like NASA Eagleworks has replicated the results in a vacuum in the lab:
Quote
However, Paul March, an engineer at NASA Eagleworks, recently reported in NASASpaceFlight.comís forum (on a thread now over 500,000 views) that NASA has successfully tested their EM Drive in a hard vacuum Ė the first time any organization has reported such a successful test.

To this end, NASA Eagleworks has now nullified the prevailing hypothesis that thrust measurements were due to thermal convection.

No the gas in a car is not reaction mass. An electric car has no gas and does the same thing. You don't seem to know what I mean by reaction mass. If you are on roller skates and throw a brick that is your reaction mass. For a car the earth is its reaction mass. That is what it is reacting against. But unlike a rocket it does not have to carry its reaction mass with it.

And a car going twice as fast has four times the Ke. That energy has to come from somewhere. Chemical, electrical whatever.

Offline ppnl

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #150 on: 04/30/2015 09:31 PM »
What I'm not following from ppnl's (and other perpetual-motion theorizers') argument is how a constant thrust, sans propellant, results in a perpetual-motion, inventing-energy-from-nowhere scheme. Surely, even with a propellant-based thruster, there exists some threshold V relative to some reference frame, wherein the loss of M from propulsion is completely dominated by the increase in V, since KE = (1/2)M*V2?

Looking at KE, or dKE/dt, seems fallacious to me for that reason. Maybe I just don't understand the math well enough.

It isn't clear to me what you are saying here.

Take a car. It takes four times as much energy to accelerate from 10 mph to 20 mph as it took to accelerate from zero to ten mph. A rocket has the same problem but much worse because it takes its reaction mass with it.
A car doesn't contain reaction mass? What about gasoline?

Also, it doesn't take 4x the energy to double a car's velocity. A car has 4x the KE after doubling velocity, but that is not the same thing as saying 4x KE was required to get there.

Not to mention, the energy requirements of accelerating a car include overcoming wind resistance and friction, which resists the forward motion of the car. Maintaining a velocity against these forces is a measure of work, not energy. And since the formula for the force of drag resistance also includes V2, that means that there is 4x as much drag at 20mph as there is at 10mph, and so 4x as much work is required to maintain velocity each time you double velocity. This is still not the same thing as 4x as much energy.


Sorry, I keep replying to the wrong message.

No the gas in a car is not reaction mass. An electric car has no gas and does the same thing. You don't seem to know what I mean by reaction mass. If you are on roller skates and throw a brick that is your reaction mass. For a car the earth is its reaction mass. That is what it is reacting against. But unlike a rocket it does not have to carry its reaction mass with it.

And a car going twice as fast has four times the Ke. That energy has to come from somewhere. Chemical, electrical whatever. I did misstate a little. If it takes one unit of energy to reach x velocity it will take 3 units to go from there to 2x velocity. Four in total. Again Ke is just energy that has to come from a chemical or electrical source.

Wind resistance and other energy losses are irrelevant to this discussion as they can in principle be made as small as you like. We can assume they are zero for our purposes.

Offline gospacex

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #151 on: 04/30/2015 09:32 PM »
Taking conservation of energy literally or dogmatically, then energy can neither be created nor destroyed, and hence should be Zero in any coordinate at any given instance in time.

The latter does not follow from the former.

If you want to avoid supernatural influence in shape of gods or other unphysical things that can magically pull any trick they want, it does.

No. There are theories in which the past has no beginning (say, cyclic Big Bang/Big Crunch models). In such theories, energy "was always there", there was no point in time when it had to be created.

Offline gospacex

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #152 on: 04/30/2015 09:35 PM »
(snip...)
The thing to do now is to provide extraordinary, compelling evidence. Experiment needs to be redone in a much more clean environment. Eventually, if/when tests in vacuum but on Earth seem to still show the effect, it will need to be redone in space, away from Earth magnetic field, IR radiation etc.

*THEN* the claims will be taken by most scientists very seriously.

From the article, it looks like NASA Eagleworks has replicated the results in a vacuum in the lab:

I know. I did read the article. However, on Earth, vacuum chambers by necessity, are small. It's hard to be sure that some unforeseen electromagnetic interaction still managed to spoil the experiment. This experiment is not yet convincing enough to support the extraordinary claim made.

Online Nilof

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #153 on: 04/30/2015 09:37 PM »
What I'm not following from ppnl's (and other perpetual-motion theorizers') argument is how a constant thrust, sans propellant, results in a perpetual-motion, inventing-energy-from-nowhere scheme. Surely, even with a propellant-based thruster, there exists some threshold V relative to some reference frame, wherein the loss of M from propulsion is completely dominated by the increase in V, since KE = (1/2)M*V2?

Looking at KE, or dKE/dt, seems fallacious to me for that reason. Maybe I just don't understand the math well enough.

This part is simple newtonian mechanics. Work = force * distance. So outputPower = Work / unit time = force * distance/unit time = force * velocity.

For the EM drive, the article implies a linear relation between thrust and input power independent of the velocity: thrust = efficiency*inputPower, so we have we have outputPower = inputPower*efficiency*velocity.

So for velocity > 1/efficiency, we get outputPower > inputPower. If this threshold velocity is a few hundred m/s as implied by the numbers given in the article, you can easily stick the EM-drive on a flywheel with a tip velocity higher than 1/efficiency, and feed more than enough energy into the rotation of the flywheel to power the drive if you connect a generator to the flywheel.

Ergo, if you are proposing a mission to Saturn or alpha centauri as in the article, implying that you have a black box constant acceleration drive, you don't need any nuclear reactor to power the drive. You can just use the same kind of drive that is used for propulsion for power generation.

The reason why it doesn't lead to energy nonconservation for rockets is that you'd have to accelerate the propellant to the tip velocity of the flywheel first. But you don't have that problem with a drive that requires no propellant. Although even in that case, it is still a common way to turn heat and pressure into mechanical energy(see reaction turbines).
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline A_M_Swallow

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #154 on: 04/30/2015 09:52 PM »
From the article the Chinese test "... higher input power (2.5kW) and tested thrust (720mN) levels of an EM Drive."

For equipment massing say 10 kg using F = m a if placed on a mini rail track this should produce an acceleration of
0.72 N / 10 kg = 0.072 m/s2

Using v = u + a t after 10 seconds the vehicle could reach 0.072 m/s2 * 10 s = 0.72 m/s (=1.6 mph)
That is a speed we can see with our eyes.

The power may have to be passed through the rails. Friction and air resistance will produce a slower speed. The weight is a guess.

This experimental setup will allow directional effects and possibly velocity effects to be tested. NASA may have a sufficiently large vacuum test chamber.

Online Nilof

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #155 on: 04/30/2015 10:16 PM »
Taking conservation of energy literally or dogmatically, then energy can neither be created nor destroyed, and hence should be Zero in any coordinate at any given instance in time.

The latter does not follow from the former.

If you want to avoid supernatural influence in shape of gods or other unphysical things that can magically pull any trick they want, it does.

Conservation of energy is not a fundamental law of the universe. The more fundamental relation is Noether's theorem, which with very general assumptions tells you exactly when and why quantities like energy and momentum are conserved, and when they are useful quantities to define. Specifically, they are conserved because of symmetries.

In particular, energy is not conserved on long time scales in an expanding universe. Light does lose energy to cosmological redshift, for example. But energy and momentum certainly is conserved locally by both general relativity, the standard model, and by pretty much every form of quantum gravity proposal such as string theory, since those are all described by Lagrangians and thus obey Noether's theorem.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline CW

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #156 on: 04/30/2015 10:36 PM »
Taking conservation of energy literally or dogmatically, then energy can neither be created nor destroyed, and hence should be Zero in any coordinate at any given instance in time.

The latter does not follow from the former.

If you want to avoid supernatural influence in shape of gods or other unphysical things that can magically pull any trick they want, it does.

No. There are theories in which the past has no beginning (say, cyclic Big Bang/Big Crunch models). In such theories, energy "was always there", there was no point in time when it had to be created.

What value is a theory that can never be tested? At best, it's a hypothesis. Sounds an awful lot like religion to me.
Reality is weirder than fiction

Offline Stormbringer

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #157 on: 04/30/2015 10:45 PM »
Those cosmologies are testable though. measurements of expansion, total mass, the cosmic  background radiation and so forth have shot them down in the past. But recent questions thrown onto the expansion rate have possibly opened them up again.
« Last Edit: 04/30/2015 11:54 PM by Stormbringer »
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Offline gospacex

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #158 on: 04/30/2015 11:45 PM »
Taking conservation of energy literally or dogmatically, then energy can neither be created nor destroyed, and hence should be Zero in any coordinate at any given instance in time.

The latter does not follow from the former.

If you want to avoid supernatural influence in shape of gods or other unphysical things that can magically pull any trick they want, it does.

No. There are theories in which the past has no beginning (say, cyclic Big Bang/Big Crunch models). In such theories, energy "was always there", there was no point in time when it had to be created.

What value is a theory that can never be tested? At best, it's a hypothesis. Sounds an awful lot like religion to me.

You seem to be trying to derail my argument by switching the subject. I hope, unwillingly.

My point is not that cyclic Universe theory is a correct description of Universe.

My point is, existence of energy does not prove its nonconservation: there are logically consistent theories which have nonzero energy but have no point in time where it jumped from zero to nonzero.

Online Robotbeat

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #159 on: 05/01/2015 12:14 AM »
When you have eliminated the impossible, whatever remains, however improbable, must be the truth...
http://en.wikipedia.org/wiki/Bayesian_statistics

You're still much more likely to have fooled yourself than to have found something that is impossible by the known and most well-accepted laws of physics.
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