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#3000 by JPLeRouzic on 07 Nov, 2014 07:44
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I think the main reason why intelligent people do make statements like the constant thrust/power ratio, has nothing to do with science or engineering and nobody here will like this reason, hence my reference to a book from Umberto Eco at the end of this post.
The reason some people at JSC did this is because they wanted to keep their job in Houston after the closure of the Space shuttle progam several years ago.
I was at the first two 100YSS conferences and dr White didn't make any bold statement, he just presented dr Alcubierre work with the added notions of "boost" and yet another bubble shape. Incidently he never mention more recent work like Natario's drive or Wisser's work. He seems as Paul Gilster put it: A shy guy who doesn't seek all that PR.
There were an incredible number of people in the room where he presented his work at first 100YSS and it seems he was the main reason DARPA created this conference. At least I understood it that way.
Those JSC people have also support from Texas politicians as well as from NASA's director: http://www.usnews.com/news/articles/2012/09/18/nasa-head-bolden-warp-speed-ahead
Once such powerful people are involved, there is only one possibility for JSC people: To continue quietly in this direction as long as needed until the ambient noise makes it disappear under the radar. Hence the scarcity of information about that warp drive/EMDrive stuff.
One may find Eco's book having a lot of similarities with the present topic, especially the huge interest it gathered, if only you replace the Templar's treasure with propellantless propulsion : http://en.wikipedia.org/wiki/Foucault%27s_Pendulum
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#3001 by Mulletron on 07 Nov, 2014 07:45
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I think it is safe to say that a lot of work and a new way of thinking is needed in order to understand quantum rocket science.
This is bleeding edge stuff here. I'm not putting things to bed because I don't fully understand them yet. Since nobody is able to teach me about quantum rocket science, I have to teach myself. Unfortunately I don't have an unlimited IQ. I try, I try. I try to learn more. I have a love for learning new things and I'm a dreamer. While I lack in advanced mathematical ability beyond EE, I am an expert in systems thinking and logically solving problems.
I really really wish more people were on here with fresh perspective and experience. This group has shrunk to just a small number of the original contributors and I feel that just as I am hitting a wall, the group may be as well.
Now back to the books on nuclear powered paradoxes. -
#3002 by Mulletron on 07 Nov, 2014 08:38
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Concerning the "paradox" of conservation of energy. First I want to completely make sure I am addressing the problem, which is, folks are saying at some point the kinetic energy of the vehicle is exceeding the energy provided by the propulsion system...
Now I'm going to put controls in place:
1. I know that there is no such thing as a perpetual motion machine.
2. There is no such thing as an infinite store of energy device.
Now I'm going to build a model system:
1. The craft's mass is 100,000kg (50kg/kWe) (Middle of the road from the paper's 45 - 55 kg/kWe)
2. It has a 2MW fusion reactor on board.
3. The craft has a range of thrust to power ratios of 0.4 – 4.0 N/kWe
Specs above are from page 1 of http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140013174.pdf
Are the starting conditions good?
GO!
This is all going to boil down to Casimir momentum in the end.
I keep having to remind myself to not think of this like a reaction engine expelling a reaction mass. Instead I have to approach it from the standpoint of knowing the QV is doing the pushing.
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#3003 by JohnFornaro on 07 Nov, 2014 12:28
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Umberto Eco
Two points for Gryffindor on the reference to Foucalt's Pendulum, and its literary, but accurate, comparison to propellantless propulsion.
I might add Hypatia's observation: "God has left shadows of truth in the depths of the heart in each of us, and it is a matter of bringing them forth."
The shadow of truth is that mankind has incomplete knowledge of physics.
Do carry on. -
#3004 by Ron Stahl on 07 Nov, 2014 13:49
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I would be glad to hear about a sensible solution to the "energy paradox" of propellantless propulsion schemes, because if one is to believe to constant thrust/power ratio of the order of 1N/kW (and this clearly appear to be the case when proponents put forward amazing mission profiles) then one surely has a better option than messing around with nuclear fuel (be it for fission or fusion) : use auxiliary thrusters on a fast rotating shaft, extract
That is exactly why. No one involved in this sort of work wants to be associated with the free energy crowd, even if what they're working on might be a way to harvest a new energy source. they don't even want association with such things, in just the same way that all advanced propulsion seeks to distance itself completely from anyone bandying about the term "anti-gravity". That term was ridiculed into uselessness back in the 50's and 60's so everyone avoids it like the plague.freeunlimited energy, usefreeunlimited energy to power main thruster => infinite ISP rocket. . .
I don't know why people doing the mission profiles at 1N/kW are not advocating this obvious consequence of 1N/kW. Save maybe that "unlimited energy" would be immediately labelled crackpottery while "unlimited momentum". . . -
#3005 by Ron Stahl on 07 Nov, 2014 14:05
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. . .However, we know that QFT is incomplete, requiring reconciliation with General Relativity. . .
It's interesting that one of the features of the Standard Model is that it does not include gravity and so is not background independent. I think one of the most remarkable issues that rise out of the advanced propulsion field is Woodward's theory about the electron. His electron model is the best I have ever seen and the only electron model that actually accounts for all the components and needs necessary to such a model. It is the only electron modeI'm aware of that actually obtains as a workable model without stipulated qualifications and limitations, and it is easy to test.
If Woodward is right, he has gone an enormous way toward bringing QM and GR together finally and it should not be long before we have a theory of quantum gravity. The electron model is that sweeping in its import. Likewise too it would seem to explain dark energy. You'd think people would want to check and see if electrons have a negative bare mass, as this is such a critical issue. -
#3006 by Ron Stahl on 07 Nov, 2014 14:13
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I think the main reason why intelligent people do make statements like the constant thrust/power ratio, has nothing to do with science or engineering and nobody here will like this reason, hence my reference to a book from Umberto Eco at the end of this post.
I think you think these jobs are more fragile than they really are. All of SLS is a jobs program. It does't ever have to work. It just needs to provide jobs. Once it's complete, it should provide launch at about 10X the cost that Falcon does, so who in their right mind would use it? No one. It's a job's program. Congress is completely willing to sidetrack all of NASA's human spaceflight funding in order to provide those jobs, so obviously the jobs are not fragile.
The reason some people at JSC did this is because they wanted to keep their job in Houston after the closure of the Space shuttle progam several years ago.
Besides, Dr. White came up with his QVF conjecture years before Shuttle was retired. -
#3007 by JohnFornaro on 07 Nov, 2014 15:03
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It doesn't make sense to me to read that Woodward's electron model is"easy to test", and then read that "if the model is correct", that all HSF would be transformed and enabled, and physics would change, and all that.
Shouldn't all this "easy"testing be done first? And then all that transformation? -
#3008 by frobnicat on 07 Nov, 2014 17:00
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I would be glad to hear about a sensible solution to the "energy paradox" of propellantless propulsion schemes, because if one is to believe to constant thrust/power ratio of the order of 1N/kW (and this clearly appear to be the case when proponents put forward amazing mission profiles) then one surely has a better option than messing around with nuclear fuel (be it for fission or fusion) : use auxiliary thrusters on a fast rotating shaft, extract
That is exactly why. No one involved in this sort of work wants to be associated with the free energy crowd, even if what they're working on might be a way to harvest a new energy source. they don't even want association with such things, in just the same way that all advanced propulsion seeks to distance itself completely from anyone bandying about the term "anti-gravity". That term was ridiculed into uselessness back in the 50's and 60's so everyone avoids it like the plague.freeunlimited energy, usefreeunlimited energy to power main thruster => infinite ISP rocket. . .
I don't know why people doing the mission profiles at 1N/kW are not advocating this obvious consequence of 1N/kW. Save maybe that "unlimited energy" would be immediately labelled crackpottery while "unlimited momentum". . .
Okay, that makes sense (sociologically). But the problem is that, to have interesting mission profiles to "sell" they are necessarily having ships with more kinetic energy than was put out by generators, this is really central to the fact that propellantless missions get so interesting. Even if we had a straight asphalt road from Earth to Saturn and had wheels to push on it at many km/s, even with this "unlimited momentum" at our disposal all along the way, we would still be far from the propellentless mission profiles velocities. Quantitative estimations on request. So really, reaching such fast direct transits as Saturn in 260 days and deltaV of 200km/s (fig. 11) is not a problem of momentum, this is a problem of energy.
So in the end this is just "free energy in disguise". Think it's not good to have things in disguise in science, this is not sane. I'm ready to hear that those thrusters emit tachyons (negative energy). I'm ready to hear that quantum vacuum is like criss-crossing asphalt roads at all velocities and you can choose to push on the ones that are slow relative to you, taking at low energy cost (possibly 0) the intrinsic energy from those conveyor belts. That would be crazy but that would be all right : any idea without hidden secrets or "mysteries" or mystifications has a right to be expressed in science. Over unit energy gain issues are central to the functioning and understanding to propellantless schemes if they are to exist.
I'm not ready to hear about canards like the ones flying on Appendix A page 11 of above linked paper. More about that when I calm down : something really outrageous is going on in this Appendix. Second column. Read it well, read it again, check the maths.... this is both gross and subtle.
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#3009 by frobnicat on 07 Nov, 2014 18:54
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Concerning the Appendix A in the latest retrieved by Rodal public paper of B. Kent Joosten and Harold Human Outer Solar System Exploration via Q-Thruster Technology I said this was a spectacularly failed attempt at dealing with the problem of energy conservation for propellantless schemes.
After reading again, it appears to be an excellent exercise in deception. Whether it is self-deception (by haste, incompetence, lack of proof reading before cosigning) or voluntary deception (fraudulent) is left to the reader's opinion.
It starts by stating that, roughly, something fishy is going on with energy conservation.
<<When will the spacecraft with its given power level reach a state where the integral of the input power over a given time frame increase the kinetic energy of the spacecraft such that the change in kinetic energy is greater than the integral of power?>>
Good thing to ask, because at some point we have gained more energy than we have spent, and this would indeed be something to explain, somehow. From a conventional science standpoint, saying it like that is an understatement : this should be an absolute top priority if a theory or experimental result isn't to be thrashed. Appears from the following calculation that this is when deltaV = 2/Ts that is twice the inverse of Ts the thrust/power ratio. Q-Thruster with a specific thrust Ts of 0.4 N/kWe <<A conservative Q-Thruster specific thrust assumption (0.4 N/kWe)>> will reach that deltaV at 2/.4e-3 = 5000 m/s = 5km/s. Note that the studied mission profiles go way beyong this deltaV, citing 100km/s for max velocity during transit to Saturn. So we were going to Saturn through the realm of "more gained energy than spent" for the most part.
A note on passing : this is just a factor two (we could as well ignore that little term and proceed) but it should be understood that, at velocity V relative to a given (more or less inertial) frame the over unit energy gain appears at V = 1/Ts. The 2 term comes when you consider the journey overall. From the standpoint of the rest frame from where the ship started, the ship is not gaining more energy than spent until half of the journey to 2/Ts, this first half part averages with the second half where the ship is always gaining more than spending. This second "phase" starts as soon as V>1/Ts. So the "problematic speed" is 2.5kms really.
Instantly_Recoverable_Mechanical_Power = Pout = V*Thrust = V*Ts*Pin
Pout/Pin = V*Ts Pout/Pin>1 => V*Ts>1 => V>1/Ts
Full frontal "more gained energy than spent" should be thrashed, or so it should be said to appear "scientifically correct". So the appendix goes on to say that
<<When this situation occurs, in order to ensure that the input energy is equal to the change in kinetic energy, the thrust to power performance will have to decrease over time.>>
I would rather say "performance will decrease over ever increasing speed".
All right then. Decrease by how much ? Does that hurt the mission profiles badly ? You bet it should ! This decrease factor is starting at Vc=1/Ts=2.5km/s and we want 100km/s. The "over unit power amplification factor" is proportional to V : Pout/Pin=V*Ts=V/Vc so we are betting on average (at 50km/s) on 20 times more efficiency than energy conservation decency should allow. Do we hear anything about that by the authors who have spent 10 pages on interplanetary go-fasts ? No. Silence about the consequences of that scientific decency requirement on the race-spaceships above.
Instead we hear that <<This scenario has an analog in the terrestrial realm when considering a turbine aircraft flight profile. At takeoff, the turbine aircraft has a very high thrust to power (hundreds of N/kW), but at cruise altitude, the thrust to power performance is much lower (1-10 N/kW). The following graph shows the curve with some highlighted data points for consideration.>>
I would add : take a road and a car and you have the same problem, it's proportionally harder to push on a "momentum medium" when having more velocity relative to this medium : power_required=V*Force.
So this is factually correct. This remark would make the subject advance if it served as an introduction as to "how are we supposed to define the rest frame of a momentum exchanging medium in interplanetary deep space ?". The later invocation of CMB rest frame is a joke as we will see. At this point I rather expected a wild but "crystal clear", or at least explicit speculation, that since vacuum defines no intrinsic rest frame (relativity...), we are "kind of always pushing it at 0 or near so relative speed" so that we have power_required=0*Force=0 or near so. A conveyor belt model for the vacuum. Don't know if that can be made theoretically sound, maybe Mulletron you are on this track when stating that we shouldn't consider pushing on but being pushed on.
Instead we have a graph with this Vc=1/Ts (or rather 2/Ts but really it should be 1/Ts) comparing Hall thruster at 0.056N/kWe, with a higher velocity around 30km/s ( beyond which ... what, it will gain more energy than spent ? We will see... ) than devices of higher Ts. That's basic rocket science that as Isp augments you have less mass penalty to reach higher deltaV but that Ts is lowered, things get less mass starved and more energy starved. On top left there would be the photon rocket. On bottom right there would be someone launching away a heavy bag while standing on a skateboard (10kg bag, 1m/s, that's 5J for 10kg m/s momentum or equivalently 2000N/kW, yes, that much, very power efficient, but very mass inefficient).
Obviously the great advantage of propellantless schemes with Ts>>1/c (photon rocket) would be to have better Ts than high Isp action/reaction, and yet having to throw out no mass like the better Ts schemes (chemical rockets) that get mass exhausted quickly.
Ok, so ?
Better is below this graph...
<<The change in kinetic energy as measured by the inertial observer at rest relative to the background radiation is the initial kinetic energy ... minus the final kinetic energy ... .>>
... will proceed after a deep yoga breathing session.
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#3010 by Rodal on 07 Nov, 2014 19:15
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.....
This was for one Shawyer's thrust vs power graph. I prefer to concentrate on Brady, as someone put it (you ? Aero ? Mulletron ?) it is better documented, and maybe of more reliable value. I don't completely give up on this "warm jet effect". Even if it seems unlikely it would have been gone unnoticed and gave results somehow in agreements between different labs, the alternatives are either as much hazardous (magnetic couplings) or more hard to swallow (axions anyone ?)
We don't even know from the experimenters the most basic geometric characteristics of their device. Who know (save them) how much they are tinkering with things before "it works", what kind of "secret recipe" procedures are followed and in which we could maybe see some confirmation or invalidation of such or such possible explanation. One thing stands out : the effect is hard to get at, and that's not because of ultra faint magnitude (µN when nN are "routinely" investigated with short range gravitation studies). So what makes it so hard to make it reproducible and reliable ? Driving a high Q at resonant frequency ? Mmm. Well. Maybe. Only maybe.
My latest derivation for the warm air jet hypothesis : F in function of microwave volumetric heating Pow and tau time constant of the rise/fall
F = Cf/rho * ((2*p*Tau)/V)^0.5 * (Pow/(C*T))^1.5
That is by using numerical values for almost constants ( 20°C ambient ... )
F = 1.41e-6 * 1/sqrt(V) * sqrt(Tau) * Pow^1.5
V=0.027m^3 Tau=2s Pow=4W yields F=97µN
But that needs tinkering until the leak area A is small enough (but not stoppered) to give high thrust, but big enough so that Tau is below some level (otherwise you see a ramp up). How much tinkering is going on ?
F = 9.7e-12 * Pow^2/A
Tau = 4.74e-11 * V*Pow/A^2
Intuitively I'm in favor of some electromagnetic explanation, but think this is still worth investigating.
Frobnicat, I haven't heard about your warm air propulsion model since your last message reproduced above.
I'm not clear as to what should be the forcing function as a function of time to input for the pendulum analysis, as per your model
For this
F = 1.41e-6 * 1/sqrt(V) * sqrt(Tau) * Pow^1.5
appears as a constant with tau = 2 seconds.
What is your forcing function for your warm air propulsion model as an explicit function of time? -
#3011 by JohnFornaro on 07 Nov, 2014 19:40
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Second column. Read it well, read it again, check the maths.... this is both gross and subtle.
Me not get it. Per that scenario in Column 2 on page 11, if ya go from 0km/sec to 1km/ sec, and your spacecraft drops from 10,000kg to 9460 kg, you end up at -4,730J J.
Your pragmatic inertial frame would be the galaxy, wouldn't it? Let's say I'm at the Equator here on Eaarth, standing still. Yet, I'm going a thousand miles an hour more or less. I can't use that energy in any pragmatic fashion. My rest frame is on the Equator, not in "absolute" space.
So what's the point of this "paradox"?
Why do they call it a "peculiar" velocity? Why isn't it just a velocity relative to the CMB? -
#3012 by JPLeRouzic on 07 Nov, 2014 19:43
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something really outrageous is going on in this Appendix. Second column. Read it well, read it again, check the maths.... this is both gross and subtle.
You mean what people call the "kinetic energy paradox"? That kinetic energy is proportional to the square of speed?
https://www.physicsforums.com/threads/kinetic-energy-and-frames-of-reference.534883/
It is what you already mention as a paradox as well as GoatGuy and it is also used in this linked paper.
What physicists say, is that one can't add up kinetic energy in different reference frames (nothing to do with relativity).
In my opinion every people using a metric like trust/power for several segments of the same travel, are doing exactly this mistake...adding kinetic energy in different reference frames -
#3013 by frobnicat on 07 Nov, 2014 20:48
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.....
Frobnicat, I haven't heard about your warm air propulsion model since your last message reproduced above.
I'm not clear as to what should be the forcing function as a function of time to input for the pendulum analysis, as per your model
For this
F = 1.41e-6 * 1/sqrt(V) * sqrt(Tau) * Pow^1.5
appears as a constant with tau = 2 seconds.
What is your forcing function for your warm air propulsion model as an explicit function of time?
This formula is for the thrust when a stationary phase (well, temporarily stationary since we are expelling air, at some point it would decrease, but this would be on the order of few minutes, will quantify all that) is reached when (heat driven) overpressure inside the cavity is stabilising relative to the leaked flow. At this stage the constant rate of increasing temperature gives a constant rate of air leak flow (before it loses too much density, few minutes later).
At the moment I don't have a satisfying F(t) expression, this amounts to formalising and solving a differential equation. At the moment I don't have this differential equation either
but I will, and will post as soon as I have. So what I have at the moment is a simplified 2 phases model : first phase as if there is no leak and pressure is growing with temperature, second phase "stationary" when the pressure is high enough for the leak to have flow that compensate for the heating rate. Obviously in reality there would be a continuous transition from phase 1 asymptotically to phase 2. The phase 1 gives the Tau (this is approximative), the phase 2 gives the magnitude of the plateau (this is exact), but unfortunately this simplified model says nothing of the progression of thrust from 0 to F (at phase 1 we are assuming no leak yet).
Hope this is not a disappointment : this is still very preliminary. I do intend to keep on with the subject until a clear quantitative model gives F(t) in function of some explicit parameters. Also have to make it all again from scratch because I think that the hole in thin plate leak formula is not the right one, must go with Hagen-Poiseuille : surely the leaks would have small lateral dimensions relative to length, more like slit (say, between copper part and pcbs end plates). My guess is that it will change the exponent that's on Pow.
Have also to check microwave coupling with water vapor.
Have also to check the heat(t) at the inner surface of copper (might be higher/faster than expected) as a rise of temperature of 10° on 100cm^3 can give as much "oomph" as 5° on 200cm^3 or 1° on 1000cm^3, so lack of thermal conductivity of air might not be the relevant factor to set the typical Tau. + some heat equations...
Have also to finish to scrap the relevant data (and share)
Have also to, damn, forgot, oh yeah, try an explicit F(t) reconstruction from the said scraped data
Have also to rant about the latest propellantless propulsion paper at hand
So, a lot of work. And this is not all my usual area of expertise. Must learn, or relearn a lot.
Please be patient. Gimme 3 weeks or so.
Maybe if you are working on heat conduction aspects at the cavity's wall, this might help me if you have an idea of the Temp(t) of the inner skin. I know that copper is a very good thermal, conductor. The epoxy behind the (probably) much thinner copper of PCBs end plate not that much. The RF power is dissipated in the first µm depth skin. What gives instant temperature for the air molecules hitting the inner walls ? This could be a fast alternative to volumetric humid air heating.
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#3014 by frobnicat on 08 Nov, 2014 00:01
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http://forum.nasaspaceflight.com/index.php?topic=29276.msg1285083#msg1285083 continued
@John & JP hope this will indirectly address your remarks, can answer more specifically if more clarifications needed.
The following reading is a little bit paranoid, and might see more intent than there really is...
So far, the offending Appendix A has stated that something fishy is going on about energy conservation with propellantless schemes. There should be some correction term depending on speed (relative to what is still unclear). Not stated : for energy conservation the correction would be severe, but we won't try to see how it would affect our fast trajectories (main body of paper). We are given a chart comparing various Thrust/Power ratios to see that from this point of view a Q-thruster is comparatively only an improvement on a Hall thruster, same ballpark just about one order of magnitude better. No crazy values, Hall thrusters are proven, and we are not pretending to be a million time better. What we are to think of the fact that on the vertical axis the Hall thruster has a higher "Delta-V Limit (absolute frames)" is left uncommented. For action/reaction scheme this "Delta-V limit" is of the same order as the ejection speed, and of the same order as the delta-V achievable through reasonable dry/wet mass ratios. For a propellentless scheme the dry/wet ratio is 1 for all practical purpose, so either the thrust/power don't care about "absolute frames" and this Delta-V limit is irrelevant (and energy is "tapped" from somewhere), or it does care about (for some unclear reason) and then at face value it means it is worse than Hall thruster for high delta V missions.
Instead of clarifications we have a mystification :
<<At this point, it is a useful exercise to explore this issue from a relativistic point of view, as it will uncover a paradox.>>
And then we will be shown that something fishy is going on also with a theoretically sound action/reaction system like a Hall thruster spacecraft. And the Appendix will conclude that
<<Although the example mission (with a Hall thruster) is clearly not an exotic mission and can easily be achieved in practice, the point of this paragraph is to identify that the paradox can be created for any spacecraft using conventional propulsion as well as advanced propulsion.>>
There we are : this is not a paradox or a problem with propellentless schemes, this is a paradox inherent to any spacecraft when energy is accounted for in an inertial frame fast enough relative to those typical delta Vs, because any of those has a Ts such that 1/Ts < high speeds, so surely any spacecraft can (apparently) provide more energy in kinetic form than is spent by the onboard generator. This is not a paradox with Q-thrusters, this is a paradox with relativity of velocities and how kinetic energy is accounted for in different inertial frame (we all know this is a messy business with all this square thing and non additivity...)
For instance, thought experiment, say we have a thruster at 0.05 N/kW that has a 1kW onboard generator, pushing at constant 100km/s relative to a device that receive mechanical energy (from this push) and converts it to electric energy. Then the mechanical energy received by this device is Force*speed = 0.05*100000=5kW. Surely this is enough raw mechanical energy to feed back 1kWe to the thruster ! Silly isn't it ? Note that : I didn't made any assumption on to what kind of thruster was used, the same calculations would hold for any thruster with 0.05N/kW thrust/power ratio.
We are left with this paradox, which plagues all spacecrafts when considered in some inertial frame fast enough. Surely there is some explanation everyone knows (so it's not worth talking about). Or maybe there is a deep mystery still lurking within Newtonian mechanics (so it's not worth talking about in an Appendix). But for sure Q-thruster is no fundamentally different from Hall thruster in that matter.
The peculiar velocity of our local (I mean, you know, a real velocity) relative to CMB as a preferred natural cosmic rest frame is just a gizmo to add to the mental confusion. Are we to understand it is important to find a real velocity or a natural rest frame ? This is left to the uncertainty of the reader... Fact is : take any arbitrary inertial frame with velocity>100km/s aligned with spacecraft trajectory will do the same job. Such that from this "absolute frame" a spacecraft at rest in its local frame (on its launch pad) has already 100km/s before it adds another km/s on the cheap (from its point of view) to a staggering 101km/s, and yet it would in principle take more energy to go from 100 to 101 than to go from 0 to 1. Because of the square.
100² to 101² -> needs to add 201
0² to 1² -> needs to add 1
Wow, again, seems paradoxical, as this is the same "thing", just seen from a different way...
So we have this artefact of relativity and kinetic energy accountancy. Let's live with it and see how the quantum vacuum can be modelled as a plasma we can push on...
But not so fast ! Nature is not an accountant that can be fooled around. We are given a numerical example to be convinced. The numerical example is given for Hall thruster (the thing that is serious) and we will see, again, this paradox.
<<The initial mass is 10,000 kg, the final mass is 9,460 kg. The initial velocity is 371 km/s, and the final velocity is 372 km/s.>> <<The amount of energy provided by the power source over this time frame is 174 Gigajoules.>>
We are invited to do <<The change in kinetic energy as measured by the inertial observer at rest relative to the background radiation is the initial kinetic energy 1/2 mi vi² minus the final kinetic energy 1/2 mf vf² .>>
And see that the result is <<The change in kinetic energy is 33,649 Gigajoules, which is two orders of magnitude larger than the energy provided by the power system.>>
Do the math, see for yourself, that works.
Except for one point : since when do you measure a change by subtracting a final amount from an initial amount ?
Proper handling shows that we are not gaining but losing : EKf-EKi = - 33649 GJ (minus)
How comes ? Because we are losing mass ! Hall thruster is an action/reaction scheme.
The dry mass fraction of 9460kg has more kinetic energy at 372km/s than at 371km/s
But the wet mass at 371km/s as more kinetic energy than the dry mass at 372km/s
So far we are nowhere near gaining more net energy than spent.
If we are to take into account the kinetic energy of the expelled mass of 540kg with Isp 1838, that is ejection velocity around 18km/s, from 371.5 on average, speed of expelled mass drifting behind is 353.5km/s :
Total kinetic energy initial
.5*10000*371000²
= 688205000000000
Total kinetic energy final
.5*9460*372000² + .5*540*353500²
=654556320000000 + 33739807500000
= 688296127500000
Change in kinetic energy :
final - initial
= + 91127500000 = 91.1 GJ
So we gained 91.1 GJ while <<the power source over this time frame is 174 Gigajoules.>>
There is nothing fishy going on with a Hall thruster.
On the other hand, with a Q-thruster of same Ts=0.056N/kWe which is not expelling mass, for roughly the same result, 10000kg*1000m/s=1e7 momentum will use E=1e7/Ts=178 Gigajoules (a bit more than Hall thruster since the spacecraft doesn't get lighter on the way) from onboard power source.
Total kinetic energy initial
.5*10000*371000²
= 688205000000000
Total kinetic energy final
.5*10000*372000²
=691920000000000
Change in kinetic energy :
final - initial
=3710 GJ
About 20 times more than spent.
There is something fishy going on with a Q thruster.
The same remarks would apply for any arbitrary rest frame : the sane system (Hall thruster) will never exhibit more kinetic energy change (final - initial) than spent energy.
The pathological system (Q-thruster) will sometimes exhibit more kinetic energy change than spent energy, sometimes less, depending on arbitrary frame from where kinetic energy is measured.
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#3015 by ThinkerX on 08 Nov, 2014 02:40
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And something I have been thinking about lately that fits in with Frobnicats last post: bouncing photons, and a odd version of the photon rocket.
As I understand it:
1) Photons have only one speed - lightspeed. Lightspeed, however, can vary depending on the media the light is passing through.
2) Photons have enough inertial mass, at least, to make a solar sail work - something demonstrated by NASA. Photons hit solar sail, pushing the solar sail and whatever its attached to.
3) Hence, you take a real heavy duty flashlight to 'deep space' and turn it on, the escaping photons would generate thrust. Not much thrust, but thrust.
4) And photons are surprisingly durable little critters. Estimates I have seen posted in this thread claim a photon can bounce for 40,000 - 50,000 times, before being absorbed .
So...with the above in mind:
Visualize a long tube, maybe a meter wide by two kilometers long, sealed at one end, open at the other. Around the outside of the open end, you have six or eight high power lasers arranged in a circle, aimed inside the tube at a sharp angle. The tubes interior is set up so these laser beams bounce off the interior in very precise directions. Basically, the beams bounce about every half meter. And just to be clear, the lasers are acting like photon rockets.
So...
1) When the lasers first fire, the initial thrust is backward.
2) With each bounce, the photons in each beam convey motion that is both 'sideways' and 'forward.' And the photon strikes with the same force each time.
3) Multiply that by 40,000 plus bounces, and the whole cylinder is either accelerating at a fairly decent clip, or conservation of energy is being violated.
4) Oh, and the last bounce, again requiring careful angles, is off the sealed end of the cylinder, directing the photons in a beam right down the middle of the tube.
Now, granted, you'd need a serious power plant to power this thing, and you'd probably want to tie a few dozen of them together in a frame of some sort, but it should get you to near relativistic speeds for far less energy cost than a rocket.
Unless I'm missing something critical.
Ok, time to post the explanations and cute videos showing how deep of a crater I dug this time...
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#3016 by aceshigh on 08 Nov, 2014 05:31
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hmmm... don´t the photons lose energy with each bounce? Yes, you will say that they remain at light speed after each bounce... which is true... but maybe in there we see the weird duality of light as particle and wave? If you see each photon alone, they won´t lose energy, but considering the whole light wave, it will?
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#3017 by ThinkerX on 08 Nov, 2014 07:24
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hmmm... don´t the photons lose energy with each bounce? Yes, you will say that they remain at light speed after each bounce... which is true... but maybe in there we see the weird duality of light as particle and wave? If you see each photon alone, they won´t lose energy, but considering the whole light wave, it will?
That is the part of this that has me baffled. A photon cannot loose momentum (inertia) and still be a photon, so it has to keep traveling at light speed. Which means my reasoning should be right - each photon should transfer the same amount of kinetic energy with each bounce. And lasers are a proposed means of providing photons for solar sail propulsion. Yet, if my reasoning is right, we are getting into free energy territory, which means this cannot be right.
I can see a lot of photons getting 'stopped' in the course of all these bounces, but many (half?) should make the full trip, and that is still one hell of a lot of kinetic energy.
Maybe Doctor Rodal or Mulletron can point out the glaringly obvious flaw here. -
#3018 by JPLeRouzic on 08 Nov, 2014 07:51
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Please, please Frobnicat, you are going too fast for me.
more energy to go from 100 to 101 than to go from 0 to 1. Because of the square.
100² to 101² -> needs to add 201
0² to 1² -> needs to add 1
Wow, again, seems paradoxical, as this is the same "thing", just seen from a different way...
- Nobody should add kinetic energy in different reference frames. That's not a paradox, that's plain and classical mechanics. A consequence is that nobody should use trust/power ratio.
- There is no ongoing conspiracy at NASA, only usual business in an agency that consumes 2 billions each years and wants to survive. To survive it needs people support.
People enjoy Startrek stuff (I am not joking, I really mean it). So NASA (and Discovery TV, and a handful of SF authors and some NASA consultants) feed people with the stuff they ask. That's a profitable business.
If one want serious science papers, there are many reputable sources. Science journals mostly, not conference papers, not pre-print servers, not self cited papers.
I know it may sound harsh, I don't want to be harsh, sorry for my lack of writing gift. This whole thread is going too far, intelligent people see artifacts and meaning where there is none. I am very sorry about that. -
#3019 by Mulletron on 08 Nov, 2014 08:30
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@ThinkerX The energy of light is proportional to the frequency. Higher frequency, higher energy photons. If some of that energy is given up to something else, the frequency is lower.
@JPLeRouzic et al. I called bull on the "paradox" from appendix A here (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140013174.pdf) a while ago due to a plethora of reasons. See my comments on "false paradox." Page 192. Confusing reference frames was just one of many problems with appendix A. The rest was just plain bad math.
On the subject on why there is so little data on Q thrusters from Nasa. I don't sense an underhanded scheme going on there for job security or something bad like that. I think either they don't really know why it works and don't want to ruin their reputation by putting out a paper on the theory without making sure it is correct OR they simply are holding on to the data because they simply choose to do so.
Break:
Still there are questions concerning conservation of energy relating to invoking the quantum vacuum to explain thrust from @Frobnicat and @Ron Stahl which need to be addressed. I'm not sure if there is enough info to really address those concerns. I spent all day trying to figure this out and I simply don't have enough info about the momentum of the QV. Simple as that. If there are massive particles appearing and disappearing there in and they are in motion, then they must have momentum during their brief existence.
The issue of the Nasa conjectured Q-thruster enabled fantastic mission profiles is another issue that needs serious attention, as enlightened by @Frobnicat.
I can tell you that I know there is no such thing as a free energy device so I'm chalking those concerns up as valid yet premature simply because we don't even understand Quantum Rocket Science yet. The QV is not well understood.
The fact that EMdrive demonstates that you must put energy in in order to get something out supports that we're not dealing with hocus pocus here.
Edited to add full names.
but I will, and will post as soon as I have. So what I have at the moment is a simplified 2 phases model : first phase as if there is no leak and pressure is growing with temperature, second phase "stationary" when the pressure is high enough for the leak to have flow that compensate for the heating rate. Obviously in reality there would be a continuous transition from phase 1 asymptotically to phase 2. The phase 1 gives the Tau (this is approximative), the phase 2 gives the magnitude of the plateau (this is exact), but unfortunately this simplified model says nothing of the progression of thrust from 0 to F (at phase 1 we are assuming no leak yet).