Is EmDrive actually just gibberish?
Conundrum, Wed Nov 04 2015, 02:02PMHi..
The lack of reliable replications by reputable scientists suggests to me that the whole thing could unfortunately be measurement error combined with wishful thinking.
Certainly there are a lot of people working on this, but if the effect was this obvious it would have side effects such as affecting inertia locally which simply has not been observed.
Also there seems to be no coherent theory on why a simple resonant chamber should have any anomalous thrust, the scaling effect with chamber Q factor is also very suspicious as it would lead to large jumps in efficiency inconsistent with basic thermodynamics and have other detectable side effects we would have detected already.
I do feel sorry for the people who have wasted their time and money on this, but it does suggest that a basic understanding of fundamental laws of physics is evident.
A simple balance of forces analysis proves that there is no possibility of generating thrust without reaction mass being expended.
Re: Is EmDrive actually just gibberish?
hen918, Wed Nov 04 2015, 05:39PM
We'll have to wait for peer review, I'll reserve judgement until then...
hen918, Wed Nov 04 2015, 05:39PM
We'll have to wait for peer review, I'll reserve judgement until then...
Re: Is EmDrive actually just gibberish?
BigBad, Thu Nov 05 2015, 12:14AM
It's 'technically' already been peer reviewed in Actua Physica which is a Chinese periodical, but it has an impact factor of about 2, so it's not exactly prestigious, and probably not the best peer review in the world.
But yeah, it's very, very likely to be experimental error(s).
It's probably similar to the CERN experiment where they were apparently getting transluminal neutrinos, till they figured out they'd just left the timing cable unplugged slightly.
The thing to look for is when the effect gets stronger with more accurate experiments. With the NASA experiment, the apparent signal strength went down relative to previous experiments.
If the effect was real, the effect should have been much stronger and more obvious with more sensitive experiments.
Right now, it's looking more like pathological science.
BigBad, Thu Nov 05 2015, 12:14AM
It's 'technically' already been peer reviewed in Actua Physica which is a Chinese periodical, but it has an impact factor of about 2, so it's not exactly prestigious, and probably not the best peer review in the world.
But yeah, it's very, very likely to be experimental error(s).
It's probably similar to the CERN experiment where they were apparently getting transluminal neutrinos, till they figured out they'd just left the timing cable unplugged slightly.
The thing to look for is when the effect gets stronger with more accurate experiments. With the NASA experiment, the apparent signal strength went down relative to previous experiments.
If the effect was real, the effect should have been much stronger and more obvious with more sensitive experiments.
Right now, it's looking more like pathological science.
Re: Is EmDrive actually just gibberish?
Ash Small, Sat Nov 14 2015, 08:35PM
As I understand it, and I don't think the write ups ever offered any real explanation, it's supposed to absorb EM radiation, of many different wavelengths, and 'warm up', then emit 'black body radiation', more in one direction than in others, doe to it's 'waveguide' shape.
Surely we should also consider the basic idea itself, and whether this is possible, and if so, how to construct a 'better designed apparatus' for this purpose?
Ash Small, Sat Nov 14 2015, 08:35PM
As I understand it, and I don't think the write ups ever offered any real explanation, it's supposed to absorb EM radiation, of many different wavelengths, and 'warm up', then emit 'black body radiation', more in one direction than in others, doe to it's 'waveguide' shape.
Surely we should also consider the basic idea itself, and whether this is possible, and if so, how to construct a 'better designed apparatus' for this purpose?
Re: Is EmDrive actually just gibberish?
Dr. Slack, Sun Nov 15 2015, 08:07AM
we already have the technology to emit a collimated beam of photons, in whatever direction we want, at high powers, basically a photon rocket. Emitting back body radiation, in one direction, would not improve on that.
Dr. Slack, Sun Nov 15 2015, 08:07AM
we already have the technology to emit a collimated beam of photons, in whatever direction we want, at high powers, basically a photon rocket. Emitting back body radiation, in one direction, would not improve on that.
Re: Is EmDrive actually just gibberish?
BigBad, Mon Nov 16 2015, 03:48AM
BigBad, Mon Nov 16 2015, 03:48AM
Ash Small wrote ...
As I understand it, and I don't think the write ups ever offered any real explanation, it's supposed to absorb EM radiation, of many different wavelengths, and 'warm up', then emit 'black body radiation', more in one direction than in others, doe to it's 'waveguide' shape.
No, that would be a type of photon rocket; it supposedly wayyyy outperforms a photon rocket.As I understand it, and I don't think the write ups ever offered any real explanation, it's supposed to absorb EM radiation, of many different wavelengths, and 'warm up', then emit 'black body radiation', more in one direction than in others, doe to it's 'waveguide' shape.
Re: Is EmDrive actually just gibberish?
Ash Small, Tue Nov 17 2015, 04:36AM
Well, I think everyone agrees the results aren't accurate. NASA even said there were problems with their setup, but didn't bother to investigate further.
Surely a 'proton rocket' would be worth pursuing anyway, if it's powered by background EM waves in space it will still keep accelerating indefinitely........?
Ash Small, Tue Nov 17 2015, 04:36AM
Well, I think everyone agrees the results aren't accurate. NASA even said there were problems with their setup, but didn't bother to investigate further.
Surely a 'proton rocket' would be worth pursuing anyway, if it's powered by background EM waves in space it will still keep accelerating indefinitely........?
Re: Is EmDrive actually just gibberish?
Dr. Slack, Tue Nov 17 2015, 08:07AM
We've already got proton rockets (OK, you need a few neutrons as well to keep the clumps of them stable, and some electrons to keep them overall neutral) and they have a good specific impulse, but the problem is you need a tank of them. Harvesting them from the interstellar medium so you don't need to carry them with you has often been mooted, but it's only pie in the sky at the moment.
We can easily make photon rockets, but their specific impulse is $hite. Shining a LED or a laser out of the back is a lot more practical than heating a conic frustrum waveguide with waste heat and hoping the black body radiation comes out anisotropically. A solar sail gets two momentum exchanges for each photon, and doesn't have to fiddle about with all that energy conversion, but you can't sail into the wind, so to speak.
The EM drive was to improve over the specific impulse of photons by orders of magnitude, it would not have been worth it otherwise.
The EM drive was only ever to be powered by an on-board supply, RTG or PV. Once you are asking to harvest the background EM of space, then we are even deeper into tin-foil-hat territory than the EM drive itself. Keep a grip! Mechanism creep is a sure sign of dodgy methodology.
Dr. Slack, Tue Nov 17 2015, 08:07AM
Ash Small wrote ...
Surely a 'proton rocket' would be worth pursuing anyway, if it's powered by background EM waves in space it will still keep accelerating indefinitely........?
Surely a 'proton rocket' would be worth pursuing anyway, if it's powered by background EM waves in space it will still keep accelerating indefinitely........?
We've already got proton rockets (OK, you need a few neutrons as well to keep the clumps of them stable, and some electrons to keep them overall neutral) and they have a good specific impulse, but the problem is you need a tank of them. Harvesting them from the interstellar medium so you don't need to carry them with you has often been mooted, but it's only pie in the sky at the moment.
We can easily make photon rockets, but their specific impulse is $hite. Shining a LED or a laser out of the back is a lot more practical than heating a conic frustrum waveguide with waste heat and hoping the black body radiation comes out anisotropically. A solar sail gets two momentum exchanges for each photon, and doesn't have to fiddle about with all that energy conversion, but you can't sail into the wind, so to speak.
The EM drive was to improve over the specific impulse of photons by orders of magnitude, it would not have been worth it otherwise.
The EM drive was only ever to be powered by an on-board supply, RTG or PV. Once you are asking to harvest the background EM of space, then we are even deeper into tin-foil-hat territory than the EM drive itself. Keep a grip! Mechanism creep is a sure sign of dodgy methodology.
Re: Is EmDrive actually just gibberish?
Ash Small, Tue Nov 17 2015, 04:32PM
I still argue that in order to travel any 'significant' distance in space, it doesn't make any sense trying to carry enough fuel fo the whole journey, and that you need to harvest energy on the way. Background radiation, of one sort or another, is there in abundance.
Of course, time scales will be far longer than we can imagine, but they would be in order to travel any 'significant' distance in space, anyway.
Ash Small, Tue Nov 17 2015, 04:32PM
I still argue that in order to travel any 'significant' distance in space, it doesn't make any sense trying to carry enough fuel fo the whole journey, and that you need to harvest energy on the way. Background radiation, of one sort or another, is there in abundance.
Of course, time scales will be far longer than we can imagine, but they would be in order to travel any 'significant' distance in space, anyway.
Re: Is EmDrive actually just gibberish?
BigBad, Thu Nov 19 2015, 02:25AM
They harvest EM fields for energy and then electromagnetically emit protons and neutrons at extremely high speed to get good specific impulse.
They're called ion drives, and the device for harvesting EM fields is called a 'solar panel'
Neat, huh? ;)
Trouble is, the EM fields become very rarified in the interstellar medium.
BigBad, Thu Nov 19 2015, 02:25AM
Dr. Slack wrote ...
We've already got proton rockets (OK, you need a few neutrons as well to keep the clumps of them stable, and some electrons to keep them overall neutral) and they have a good specific impulse, but the problem is you need a tank of them. Harvesting them from the interstellar medium so you don't need to carry them with you has often been mooted, but it's only pie in the sky at the moment... Once you are asking to harvest the background EM of space, then we are even deeper into tin-foil-hat territory than the EM drive itself. Keep a grip! Mechanism creep is a sure sign of dodgy methodology.
Actually, that's how some current drives work.Ash Small wrote ...
Surely a 'proton rocket' would be worth pursuing anyway, if it's powered by background EM waves in space it will still keep accelerating indefinitely........?
Surely a 'proton rocket' would be worth pursuing anyway, if it's powered by background EM waves in space it will still keep accelerating indefinitely........?
We've already got proton rockets (OK, you need a few neutrons as well to keep the clumps of them stable, and some electrons to keep them overall neutral) and they have a good specific impulse, but the problem is you need a tank of them. Harvesting them from the interstellar medium so you don't need to carry them with you has often been mooted, but it's only pie in the sky at the moment... Once you are asking to harvest the background EM of space, then we are even deeper into tin-foil-hat territory than the EM drive itself. Keep a grip! Mechanism creep is a sure sign of dodgy methodology.
They harvest EM fields for energy and then electromagnetically emit protons and neutrons at extremely high speed to get good specific impulse.
They're called ion drives, and the device for harvesting EM fields is called a 'solar panel'
Neat, huh? ;)
Trouble is, the EM fields become very rarified in the interstellar medium.
Re: Is EmDrive actually just gibberish?
Ash Small, Thu Nov 19 2015, 11:17PM
I doubt solar panels or conventional ion drives would last anywhere near the times required to travel any 'significant' distance in space.
Something like the proposed waveguide device might stand a better chance of surviving the trip?
Ash Small, Thu Nov 19 2015, 11:17PM
I doubt solar panels or conventional ion drives would last anywhere near the times required to travel any 'significant' distance in space.
Something like the proposed waveguide device might stand a better chance of surviving the trip?
Re: Is EmDrive actually just gibberish?
Dr. Slack, Fri Nov 20 2015, 10:46AM
I could make the argument that a concrete block stands a better chance of the surviving the trip than a momentum-ejecting rocket for which we understand the mechanism of operation, and can build. I've yet to see any evidence that an EM drive works better than a warm concrete block, or even theories that are consistent with known science for how it might.
Dr. Slack, Fri Nov 20 2015, 10:46AM
Ash Small wrote ...
I doubt solar panels or conventional ion drives would last anywhere near the times required to travel any 'significant' distance in space.
Something like the proposed waveguide device might stand a better chance of surviving the trip?
I doubt solar panels or conventional ion drives would last anywhere near the times required to travel any 'significant' distance in space.
Something like the proposed waveguide device might stand a better chance of surviving the trip?
I could make the argument that a concrete block stands a better chance of the surviving the trip than a momentum-ejecting rocket for which we understand the mechanism of operation, and can build. I've yet to see any evidence that an EM drive works better than a warm concrete block, or even theories that are consistent with known science for how it might.
Re: Is EmDrive actually just gibberish?
Ash Small, Fri Nov 20 2015, 01:24PM
I agree that the results are so far inconclusive
Ash Small, Fri Nov 20 2015, 01:24PM
I agree that the results are so far inconclusive
Re: Is EmDrive actually just gibberish?
BigBad, Sat Nov 21 2015, 03:28AM
BigBad, Sat Nov 21 2015, 03:28AM
Dr. Slack wrote ...
I could make the argument that a concrete block stands a better chance of the surviving the trip than a momentum-ejecting rocket for which we understand the mechanism of operation, and can build. I've yet to see any evidence that an EM drive works better than a warm concrete block, or even theories that are consistent with known science for how it might.
lol, and it's only funny because it's true.I could make the argument that a concrete block stands a better chance of the surviving the trip than a momentum-ejecting rocket for which we understand the mechanism of operation, and can build. I've yet to see any evidence that an EM drive works better than a warm concrete block, or even theories that are consistent with known science for how it might.
Re: Is EmDrive actually just gibberish?
DekuTree64, Mon Nov 21 2016, 10:05AM
Peer reviewed study has been published: http://arc.aiaa.org/doi/10.2514/1.B36120
Apparently it produces 1.2 mN per kW. Two orders of magnitude greater than a photon rocket, and only one order of magnitude less than a propellant-consuming ion thruster. Pretty exciting!
DekuTree64, Mon Nov 21 2016, 10:05AM
Peer reviewed study has been published: http://arc.aiaa.org/doi/10.2514/1.B36120
Apparently it produces 1.2 mN per kW. Two orders of magnitude greater than a photon rocket, and only one order of magnitude less than a propellant-consuming ion thruster. Pretty exciting!
Re: Is EmDrive actually just gibberish?
nzoomed, Fri Nov 25 2016, 05:11AM
Well we may have to rewrite the laws of physics.
It appears NASA have tested it and have concluded it actually it works, but now they are trying to explain how it works!
Something that was once considered pseudo-science is no more, watch this space!
nzoomed, Fri Nov 25 2016, 05:11AM
Well we may have to rewrite the laws of physics.
It appears NASA have tested it and have concluded it actually it works, but now they are trying to explain how it works!
Something that was once considered pseudo-science is no more, watch this space!
Re: Is EmDrive actually just gibberish?
Patrick, Fri Nov 25 2016, 07:29AM
Patrick, Fri Nov 25 2016, 07:29AM
Dr. Slack wrote ...
Mechanism creep is a sure sign of dodgy methodology.
This is well said, and should be in a college textbook.Mechanism creep is a sure sign of dodgy methodology.
Re: Is EmDrive actually just gibberish?
Uspring, Fri Nov 25 2016, 02:32PM
If this device does not violate momentum conservation, it must push on something. This might be another object in the lab, which makes it unsuitable for a drive operating in space. Or it must emit some sort of particles, e.g. photons, which would just constitute some sort of standard EM drive or some other particles. If there are some other particles, these particles must be quite heavy, otherwise the thrust would be very weak, as is the case for photons. What kind of particles that might be, is unknown and there are no candidates.
But lets assume that these particles exist. Then there would be a mass loss on the drive similar to that of an ion drive or a typical rocket engine. For long term propulsion, that is a problem.
Now lets assume that the device violates momentum conservation. Momentum conservation is deeply linked to energy conservation. It is possible to build a not energy conserving machine from a not momentum conserving device. That puts us in the domain of perpetuum mobiles.
Not likely.
Uspring, Fri Nov 25 2016, 02:32PM
If this device does not violate momentum conservation, it must push on something. This might be another object in the lab, which makes it unsuitable for a drive operating in space. Or it must emit some sort of particles, e.g. photons, which would just constitute some sort of standard EM drive or some other particles. If there are some other particles, these particles must be quite heavy, otherwise the thrust would be very weak, as is the case for photons. What kind of particles that might be, is unknown and there are no candidates.
But lets assume that these particles exist. Then there would be a mass loss on the drive similar to that of an ion drive or a typical rocket engine. For long term propulsion, that is a problem.
Now lets assume that the device violates momentum conservation. Momentum conservation is deeply linked to energy conservation. It is possible to build a not energy conserving machine from a not momentum conserving device. That puts us in the domain of perpetuum mobiles.
Not likely.
Re: Is EmDrive actually just gibberish?
Dr. Slack, Fri Nov 25 2016, 04:24PM
At least this latest experiment is looking serious. They have made some good attempts to address spurious influences. No flexing cables to disturb the balance, as contacts were made through liquid metal, and an account has been taken of thermal effects. A calibration measurement before and after the thrust measurement.
These are their results, measured torque versus power.
There is certainly something going on.
I am concerned however about the variation in measured torque, especially at the 60W mark. There is not only a 3:1 variation, it's also an order of magnitude larger than their error bars. This means that something is very poorly controlled in the experimental setup, something is not reproducible.
Their calibration measurements on their torque beam are worth discussion. They are very consistent. This is good in the sense that it shows the setup is measuring the calibration torque well. This further highlights the fact that while the torque measurement system is working well to the calibration torque, it is still producing very variable device under test torques.
If the message of this paper is that we should accept the EMdrive proposal because no other explanation is available for the observed torque, then this falls far short of establishing that. While the paper does discuss other effects, I do not think that electrical effects between torque beam and chamber have been investigated sufficiently well. Extraordinary claims require extraordinary evidence, and I don't think this meets my threshhold yet.
My stance up to now has been that there is no point to performing the experiments because the theory was nonsense and experiments so far had been laughable. However, with these results, I would like to see more and better experiments, to answer the questions raised by this one. The main one in my mind is 'what is causing the wide spread of measurement results?'
I have some suggestions for the next experiments. Perhaps using the electrostatic torquer closed loop to eliminate the response time of the torsion beam, and certainly as the paper suggests better control of the thermal effects. The chamber wall proximity effects have been discussed, and they would like to move to a larger chamber. Further runs may be possible with this small chamber, using moveable baffles driven by stepper motors, which would allow 'walls' to be moved nearer to the device under test, to see if effects varied with distance.
If they're getting supposedly measurable results with only 80 watts, I wonder what the budget and enthusiasm would be for flying a test satellite equipped with this, a photon engine and an ion thruster, with ranging corner cube reflectors to allow precise orbit determination, to compare deltaVs for all three engines?
New Scientist's impeccable journalism strikes again. They had an article of about 8 column-inches in this week's issue, mentioned NASA, but said absolutely nothing of any meaning, neither referring to nor linking to their report.
Dr. Slack, Fri Nov 25 2016, 04:24PM
At least this latest experiment is looking serious. They have made some good attempts to address spurious influences. No flexing cables to disturb the balance, as contacts were made through liquid metal, and an account has been taken of thermal effects. A calibration measurement before and after the thrust measurement.
These are their results, measured torque versus power.
There is certainly something going on.
I am concerned however about the variation in measured torque, especially at the 60W mark. There is not only a 3:1 variation, it's also an order of magnitude larger than their error bars. This means that something is very poorly controlled in the experimental setup, something is not reproducible.
Their calibration measurements on their torque beam are worth discussion. They are very consistent. This is good in the sense that it shows the setup is measuring the calibration torque well. This further highlights the fact that while the torque measurement system is working well to the calibration torque, it is still producing very variable device under test torques.
If the message of this paper is that we should accept the EMdrive proposal because no other explanation is available for the observed torque, then this falls far short of establishing that. While the paper does discuss other effects, I do not think that electrical effects between torque beam and chamber have been investigated sufficiently well. Extraordinary claims require extraordinary evidence, and I don't think this meets my threshhold yet.
My stance up to now has been that there is no point to performing the experiments because the theory was nonsense and experiments so far had been laughable. However, with these results, I would like to see more and better experiments, to answer the questions raised by this one. The main one in my mind is 'what is causing the wide spread of measurement results?'
I have some suggestions for the next experiments. Perhaps using the electrostatic torquer closed loop to eliminate the response time of the torsion beam, and certainly as the paper suggests better control of the thermal effects. The chamber wall proximity effects have been discussed, and they would like to move to a larger chamber. Further runs may be possible with this small chamber, using moveable baffles driven by stepper motors, which would allow 'walls' to be moved nearer to the device under test, to see if effects varied with distance.
If they're getting supposedly measurable results with only 80 watts, I wonder what the budget and enthusiasm would be for flying a test satellite equipped with this, a photon engine and an ion thruster, with ranging corner cube reflectors to allow precise orbit determination, to compare deltaVs for all three engines?
New Scientist's impeccable journalism strikes again. They had an article of about 8 column-inches in this week's issue, mentioned NASA, but said absolutely nothing of any meaning, neither referring to nor linking to their report.
Re: Is EmDrive actually just gibberish?
Carbon_Rod, Sat Nov 26 2016, 06:54AM
Also tried to find a detailed photo of the apparatus with little success.
1.
I was curious if the trials were repeated after rotating the entire rig 90' within the earth's magnetic field.
i.e. their calculations should remain constant if not a confounding variable.
2.
If one can measure the near-field RF radiation pattern (< 1 lambda) to see if it had opportunity to couple to metal objects in the test chamber, and not the emitter probe wave guide.
3.
Overlooked something trivial like:
Although, the phenomena may still upset those emotionally invested in contradicting legacy aether theories.
I'll safely wager it will not work outside a test chamber in space...
Carbon_Rod, Sat Nov 26 2016, 06:54AM
Also tried to find a detailed photo of the apparatus with little success.
1.
I was curious if the trials were repeated after rotating the entire rig 90' within the earth's magnetic field.
i.e. their calculations should remain constant if not a confounding variable.
2.
If one can measure the near-field RF radiation pattern (< 1 lambda) to see if it had opportunity to couple to metal objects in the test chamber, and not the emitter probe wave guide.
3.
Overlooked something trivial like:
Although, the phenomena may still upset those emotionally invested in contradicting legacy aether theories.
I'll safely wager it will not work outside a test chamber in space...
Re: Is EmDrive actually just gibberish?
nzoomed, Sun Nov 27 2016, 12:19AM
I think the media are reporting it wrong though.
In our news the reporter claimed its an amazing device that gets its energy from "nothing" that can only be understood as over-unity.
nzoomed, Sun Nov 27 2016, 12:19AM
I think the media are reporting it wrong though.
In our news the reporter claimed its an amazing device that gets its energy from "nothing" that can only be understood as over-unity.
Re: Is EmDrive actually just gibberish?
Dr. Slack, Thu Dec 08 2016, 12:25PM
with the straplines ...
The 'impossible' EM Drive is about to be tested in space
Time to get to the bottom of this crazy thing
Interesting. Looks like there are not one, but two, efforts to put this damned thing into orbit.
Let the reckoning begin!
Dr. Slack, Thu Dec 08 2016, 12:25PM
with the straplines ...
The 'impossible' EM Drive is about to be tested in space
Time to get to the bottom of this crazy thing
Interesting. Looks like there are not one, but two, efforts to put this damned thing into orbit.
Let the reckoning begin!
Re: Is EmDrive actually just gibberish?
nzoomed, Thu Dec 08 2016, 11:17PM
My question is where does the electricity come from?
Solar panels?
You would need quite a large solar array to power it wouldnt you?
nzoomed, Thu Dec 08 2016, 11:17PM
My question is where does the electricity come from?
Solar panels?
You would need quite a large solar array to power it wouldnt you?
Re: Is EmDrive actually just gibberish?
BigBad, Fri Dec 09 2016, 01:55AM
I still don't believe a word of this. All the previous experiments by others have now been retracted. The NASA team have almost certainly just fucked something up.
Their experimental time/thrust curve is about 50% thermal expansion; even the NASA team admit that. That there's even any real signal beneath that is IMO super unlikely. The thrust curve they obtained takes *seconds* to decay; but given the Q-factor the microwaves are gone from the frustrum in *microseconds*.
I just don't buy it. Extraordinary claims require extraordinary evidence, and this is really, really ordinary.
BigBad, Fri Dec 09 2016, 01:55AM
I still don't believe a word of this. All the previous experiments by others have now been retracted. The NASA team have almost certainly just fucked something up.
Their experimental time/thrust curve is about 50% thermal expansion; even the NASA team admit that. That there's even any real signal beneath that is IMO super unlikely. The thrust curve they obtained takes *seconds* to decay; but given the Q-factor the microwaves are gone from the frustrum in *microseconds*.
I just don't buy it. Extraordinary claims require extraordinary evidence, and this is really, really ordinary.
Re: Is EmDrive actually just gibberish?
Uspring, Fri Dec 09 2016, 11:29AM
I once puzzled about the energetics of a rocket engine. The power supplied to the rocket is F*v, where F is the thrust and v the velocity of the rocket. Thus for high v this can be larger than the power of the combustion. How can that be?
The solution is, that the kinetic energy of the exhaust fumes has to be taken into account. When the rocket is moving at high speed, the exhaust fumes will be trailing it a lower speed. Thus the propellant as exhaust fume looses speed and kinetic energy compared to the time when it is still in the rocket. So energy conservation is restored. A quick calculation will confirm this.
Now if you have a rocket drive without a propellant the above argument can't be appled anymore. Energy won't be conserved, i.e. an EM drive is a perpetual motion machine.
Uspring, Fri Dec 09 2016, 11:29AM
I once puzzled about the energetics of a rocket engine. The power supplied to the rocket is F*v, where F is the thrust and v the velocity of the rocket. Thus for high v this can be larger than the power of the combustion. How can that be?
The solution is, that the kinetic energy of the exhaust fumes has to be taken into account. When the rocket is moving at high speed, the exhaust fumes will be trailing it a lower speed. Thus the propellant as exhaust fume looses speed and kinetic energy compared to the time when it is still in the rocket. So energy conservation is restored. A quick calculation will confirm this.
Now if you have a rocket drive without a propellant the above argument can't be appled anymore. Energy won't be conserved, i.e. an EM drive is a perpetual motion machine.
Re: Is EmDrive actually just gibberish?
hen918, Fri Dec 09 2016, 01:48PM
Now I'm an EM drive sceptic, but it isn't a rocket engine. So E=F*D like normal.
hen918, Fri Dec 09 2016, 01:48PM
Uspring wrote ...
...
Now if you have a rocket drive without a propellant the above argument can't be appled anymore. Energy won't be conserved, i.e. an EM drive is a perpetual motion machine.
...
Now if you have a rocket drive without a propellant the above argument can't be appled anymore. Energy won't be conserved, i.e. an EM drive is a perpetual motion machine.
Now I'm an EM drive sceptic, but it isn't a rocket engine. So E=F*D like normal.
Re: Is EmDrive actually just gibberish?
Uspring, Fri Dec 09 2016, 03:46PM
I'm sorry, if I haven't been clear enough. With power I meant the rate of change of energy, not energy itself. E=F*D is equivalent ot P=F*v.
If the EM drive is not similar to a rocket engine in the way, that it propels something out of the back, then this makes it a perpetual motion device.
Uspring, Fri Dec 09 2016, 03:46PM
I'm sorry, if I haven't been clear enough. With power I meant the rate of change of energy, not energy itself. E=F*D is equivalent ot P=F*v.
If the EM drive is not similar to a rocket engine in the way, that it propels something out of the back, then this makes it a perpetual motion device.
Re: Is EmDrive actually just gibberish?
hen918, Fri Dec 09 2016, 04:19PM
@Uspring
Ahh, I see, that's just me, misreading.
Yes, that's the problem I noticed with the EM drive: to obey the laws of motion *something* (quite heavy) will have to be propelled out of the cavity.
hen918, Fri Dec 09 2016, 04:19PM
@Uspring
Ahh, I see, that's just me, misreading.
Yes, that's the problem I noticed with the EM drive: to obey the laws of motion *something* (quite heavy) will have to be propelled out of the cavity.
Re: Is EmDrive actually just gibberish?
BigBad, Sun Dec 11 2016, 01:37AM
There is also some wiggle room perhaps if it works like a linear momentum wheel; you fill the cavity with microwaves, and it starts to move, and you switch it off, and it stops again. That might not even destroy the whole of physics. But it would also be a lot less useful.
But I'm still firmly in the 'it doesn't work at all camp'.
BigBad, Sun Dec 11 2016, 01:37AM
There is also some wiggle room perhaps if it works like a linear momentum wheel; you fill the cavity with microwaves, and it starts to move, and you switch it off, and it stops again. That might not even destroy the whole of physics. But it would also be a lot less useful.
But I'm still firmly in the 'it doesn't work at all camp'.
Re: Is EmDrive actually just gibberish?
Karmaslap, Sun Dec 11 2016, 10:51AM
BigBad, that would heavily violate conservation of energy and would be highly impossible with what we know of physics, with no loopholes that as current explanations afford.
If it works, conservation of momentum is sort-of broken with the radiation pressure theory which also has problems.
I'm glad they are testing the device in space, but think it will prove to not actually operate.
I'm much more excited for the Japanese satellite that will extend a cable much further into orbit in an attempt to create a satellite which will not expend fuel to keep its orbit.
Karmaslap, Sun Dec 11 2016, 10:51AM
BigBad, that would heavily violate conservation of energy and would be highly impossible with what we know of physics, with no loopholes that as current explanations afford.
If it works, conservation of momentum is sort-of broken with the radiation pressure theory which also has problems.
I'm glad they are testing the device in space, but think it will prove to not actually operate.
I'm much more excited for the Japanese satellite that will extend a cable much further into orbit in an attempt to create a satellite which will not expend fuel to keep its orbit.
Re: Is EmDrive actually just gibberish?
Sulaiman, Sun Dec 11 2016, 03:57PM
satelites flying kites ... brilliant !
(but of course you have to put the energy into the 'kite' first,
just replacing fuel/rocket with a winch/weight, or is there more to it ?)
it does look a little like a cheese-slicer to other satelites though
presumably this e-m drive is nuclear powered,
so why not just let some of the thermopile blackbody radiation radiate backwards ?
e.g. a large radioactive sheet, 'thrust' side radiates into space, the other side radiates less
as energy is extracted (thermopiles, heat-pipes, ion capture etc) from it for onboard electrical power requurements.
surely more efficient ?
Sulaiman, Sun Dec 11 2016, 03:57PM
Karmaslap wrote ...
I'm much more excited for the Japanese satellite that will extend a cable much further into orbit in an attempt to create a satellite which will not expend fuel to keep its orbit.
I'm much more excited for the Japanese satellite that will extend a cable much further into orbit in an attempt to create a satellite which will not expend fuel to keep its orbit.
satelites flying kites ... brilliant !
(but of course you have to put the energy into the 'kite' first,
just replacing fuel/rocket with a winch/weight, or is there more to it ?)
it does look a little like a cheese-slicer to other satelites though
presumably this e-m drive is nuclear powered,
so why not just let some of the thermopile blackbody radiation radiate backwards ?
e.g. a large radioactive sheet, 'thrust' side radiates into space, the other side radiates less
as energy is extracted (thermopiles, heat-pipes, ion capture etc) from it for onboard electrical power requurements.
surely more efficient ?
Re: Is EmDrive actually just gibberish?
BigBad, Tue Dec 13 2016, 07:03PM
No, you could push off the ionosphere in principle, like a linear induction motor, powered by solar panels. That way you wouldn't need any propellant.
But the coils would have to be big to interact with enough mass of plasma, but not necessarily very heavy, since wire is lightweight.
I think the emdrive test would also be solar powered.
BigBad, Tue Dec 13 2016, 07:03PM
No, you could push off the ionosphere in principle, like a linear induction motor, powered by solar panels. That way you wouldn't need any propellant.
But the coils would have to be big to interact with enough mass of plasma, but not necessarily very heavy, since wire is lightweight.
I think the emdrive test would also be solar powered.
Re: Is EmDrive actually just gibberish?
Karmaslap, Wed Dec 14 2016, 07:39AM
BigBad has it down pat. I guess the US had some issues attempting something similar and gave up after an accident, but now the Japanese are trying.
Karmaslap, Wed Dec 14 2016, 07:39AM
BigBad has it down pat. I guess the US had some issues attempting something similar and gave up after an accident, but now the Japanese are trying.
Re: Is EmDrive actually just gibberish?
johnf, Thu Jan 05 2017, 06:55PM
And
The chinese have gusumped NASA
johnf, Thu Jan 05 2017, 06:55PM
And
The chinese have gusumped NASA
Re: Is EmDrive actually just gibberish?
..., Thu Jan 05 2017, 08:31PM
Have there been any results published by the Chinese? So far all I have heard is that they 'plan to conduct a test', or have possibly have conducted a ground based test with positive (but otherwise unpublished) results.
..., Thu Jan 05 2017, 08:31PM
Have there been any results published by the Chinese? So far all I have heard is that they 'plan to conduct a test', or have possibly have conducted a ground based test with positive (but otherwise unpublished) results.
Print this page