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Quince
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Plasma propulsion
It's well known that while plasma propulsion systems generally have very high efficiency, they suffer from very low thrust (not even close to
what's needed for a launch vehicle). Apparently this has now changed:
http://www3.inspi.ufl.edu/space/program/abstracts/1146.pdf
Essentially, one ring generates a static field and acts as a nozzle, and the other one is switched, distorting the first field and accelerating the
plasma. Any conductive fluid can be used as working fluid. Can be used to get huge increases in efficiency, and even as a sort of afterburner for a
nuclear propulsion system. Much higher thrust than other plasma configurations, evenlaunch vehicle application potential.
Additionally, if someone could translate this German news release better than the crappy automatic translation, it would be great:
http://diepresse.at/Artikel.aspx?channel=h&ressort=ws&am...
Supposedly, the prototype engine was demonstrated on October 15 (can someone confirm this)?
Here's some more fascinating plasma propulsion stuff:
http://www.ess.washington.edu/Space/propulsion.html
I think it's worth starting a discussion here about DIY experiments. Let's ignore for now the problem of vacuum for testing or huge
currents needed to do the virtual plasma magnet and discuss a good plasma source. It seems RF is the way to go, to deal with the issue of electrode
erosion. Now, this is more difficult; for example, plasma chamber shape becomes critical and waveguide considerations come into play, etc. Anyone
here with knowledge about such RF applications?
[Edited on 17-10-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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12AX7
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I remember seeing something about a tapered waveguide with a plasma in the end. I don't remember if it's self-starting or if it needs an
ignition arc.
That's about all I've got...
Tim
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Marvin
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All electric solutions have 2 problems. Firstly where to get the power from and secondly common to all rockets that the more you accelerate the
exhaust the more power you need for a given thrust.
The plasma idea is midway between chemical and ion drive technology in these terms and its electric. This means its nuclear power or nothing. With
solar cells you go with ion drive and with any form of chemical power youd use a chemical rocket with better results.
Aside from anything else, as a launch method its going nowhere. Noone is going to let people use nuclear rockets in the atmosphere.
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IrC
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Another limiting factor is you have to carry your exaust with you. Whether rocket or ion propulsion, you must throw something out to move, therefore
limiting all travel and surely making interstellar travel out of the question. You can come up with cool ramscoop ideas that work on the one particle
of gas every so often but in the end you are going to run out of gas somewhere, with no way to head over to the nearby nebula and pick up some more
stuff to throw out. Only a means of propulsion which works against the very fabric of space itself is going to make it possible to go far. This is not
a whimsical idea, in fact the Casimir force does just this. So a way to utilize this effect like say a screw against the fabric of space makes sense
for vast distances, negating the need to carry your own stuff with you.
It is not outside of the realm of possibility to produce a fusion reactor that could power this space screw (or whatever it is), and not carrying a
billion metric tons of fuel would make the ship much more fuel efficient. Right now all we can think of is to throw buckets of stuff out the rear to
go forward, the idea of an electric drive which performs like an unbalanced Casimir force (or something along those lines) offers real hope in making
it to the next star system.
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Quince
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| Quote: | Originally posted by Marvin
Noone is going to let people use nuclear rockets in the atmosphere. |
This only applies to fission, not fusion. Moreover, NASA's nuclear ELECTRIC propulsion initiative is very likely to find atmospheric use.
Also, I don't think you looked at the German article I posted. The technology described is usable to enormously increase the efficiency of even
existing chemical rockets. And hey, we use nuclear engines in the oceans, don't be surprised if you see them coming to an atmosphere near you.
The 50s and 60s tests such as NERVA showed promise, and fluid core reactors in simulations are even better. But even if you forget about fission,
fusion is now really on the horizon. Otherwise, the EU/US/China/Russia/Japan/etc. wouldn't be throwing many billions of dollars to construct the
ITER reactor over the next fifteen years in France, and they are fully expecting it to WORK, over-unity.
IrC, look at the third link I posted, at the plasma magnet. Something like this can allow the creation of a virtual scoop many kilometers in size.
Plus, in interstellar travel, you are going from one solar system to another, and even if density is too low in between, there's plenty of
stellar wind ions when you approach the endpoints. You only need to carry out acceleration/decceleration at endpoints anyway, at the expense of a
longer trip.
[Edited on 17-10-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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IrC
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It is a good link Quince, I read it and have read many similar things over decades. I still would not go out there trusting to luck that I could find
some gas. At least not without taking along a copy of "Hitch Hikers Guide To The Galaxy"!
I might add it seems not a lot has been done real world to advance any of this. In 1969 I built a working ion propulsion engine and entered it into
the Kansas City Science fair that year, winning 2nd place. The IEEE gave me an award and invited me to a dinner they held yearly there with several
hundred scientists and engineers from around the world. One of them that worked at Nasa told me he had voted on mine as they were just now building
their first prototype. I don't know if that was true or if he was just trying to make a teenager feel cool, but it was a fun time. I have played
with this and fusors and other mad science ideas ever since, but I must say there is still nothing out there flying around much more advanced than
chemical rockets and jet engines. How depressing.
Ironically the guy that won 1st place did so with a Tesla coil, something I got so into in the following decades for years my coil was still the
largest one in Arizona, and Robert Golka used to come by and stay for a few days at a time while we played with insane new ideas, during this time he
was building the 2 story tall coil at Wendover AFB (and doing shows for Nova). I am somewhat happy to see Nasa working on electric propulsion using
capacitive impulse, similar to the Brown effect, and even playing around with lifters (although nobody is further along in lifter building than
Naudin). Just thought I'd throw some history in there.
If I could build a working unit as a kid a lifetime ago, surely Nasa and other agencies could start getting newer stuff up in the sky. Hopefully they
will sooner than later.
[Edited on 18-10-2005 by IrC]
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FrankRizzo
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The energy to used to create and distort the magnetic fields has to come from somewhere, no?
So, you either have a battery system onboard that's pre-charged by a chemical process or you take efficiency away from the burning propellant by
using that to generate the needed energy somehow (turbine generator,bimetallic junction, etc.).
Besides the usual crackpot junk at Jnauldin's page (jnaudin.free.fr/), the lifters that people were playing with a few years ago (and still are)
seem to operate on a similar ion acceleration principle.
[Edited on 18-10-2005 by FrankRizzo]
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Quince
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| Quote: | Originally posted by FrankRizzo
you take efficiency away from the burning propellant |
I think it's more like using some of the energy in a more efficient way. A chemical rocket does not use the chemical energy in a very efficient
way; most of the energy is wasted by not exhausting the fuel at a very high speed, not to mention the tons of unused thermal energy left in the
exhaust.
However yes, to make a real difference for a launch vehicle, a nuclear source of the electric power is needed. But NASA's already working on it.
In general, I've been disappointed that NASA is mostly looking at nuclear ELECTRIC propulsion rather than nuclear THERMAL propulsion, as the
latter is where the big thrust is. But now it seems that the practical realization of a plasma engine using Alfven waves may allow the nuclear
electric shtick to make a difference in even launch applications.
So now, how to make Alfven waves at home? 
How many kW do you think I can pull from the local pole pig before the power company gets medieval on my ass?
So hopefully I can get some suggestions here on:
-size and spacing of the two coils for a given scale of energy use (i.e. what can reasonably be gotten from house wiring)
-power proportioning between the two coils
-pulse shape and frequency for driving the non-DC coil
-how to physically do the modulation
-vacuum chamber construction (unless someone thinks a couple of kW can produce stable plasma in atmospheric pressure, which probably means need for
pre-stage to ionize the air first, such as microhollow cathode array or RF -- both difficult to implement)
Simulation is appropriate for the first two questions, but... I have the programming skill to write a highly optimized simulator, but not the plasma
physics know-how (it drives me nuts, still seeing people using slow-ass Matlab code to do large numerical simulations...). As for using an existing
simulator, I haven't the foggiest idea how to choose one...
Surely someone here knows some plasma physics and can help me get started.
[Edited on 18-10-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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IrC
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"How many kW do you think I can pull from the local pole pig before the power company gets medieval on my ass?"
I don't know laws in Canada but I have blown them up here and never got charged for replacing transformers. They can charge you for the juice you
use but not bill you for using too much. From the weatherhead in any destruction would be out of your pocket but in effect if their supply is not
large enough that really is not your fault. Assuming you have a service which can handle enough amperes to smoke the pole pig that is. Had they known
that it was transients from my end instead of the raw power consumed they may have tried to make me pay but they did not know and I was not telling. I
imagine they just thought my transformer had suffered injury during one of the august monsoons but in reality I was running my 7,500 watt Tesla coil
at the time. The crew did make remarks about my 18 foot tall extra coil but I never heard any complaints from APS. They just came out and fixed me
right up, even put in a 25 KVA pole pig to replace the 15 KVA unit I had.
Forgot to add this link on plasma patents:
http://mr-fusion.hellblazer.com/pdfs/
[Edited on 18-10-2005 by IrC]
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Quince
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Great. I'll limit myself to 5 kW (I've already made 2 kW plasma in another project, for audio purposes) and should be fine. Any comments
on my other queries?
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Mr. Wizard
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You may already know about the Farnsworth Fusor and the story of Philo T. Farnsworth, the inventor of electronic television.
If not you can start here:
http://www.belljar.net/634fusor.pdf
and Google the rest.
[Edited on 18-10-2005 by Mr. Wizard]
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IrC
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The link I posted above also contains pdf's on fusor patents. As to your question, what study I have done on the subject leads me to believe a
home lab is not going to go far, as currently powerful lasers shot into magnetized plasmas are needed. It appears the waves are produced more on
planetary or stellar scales, a little out of my reach as a mad scientist. But hey, that is what we live for right? One of us will come up with a way
to make a drive using alfven waves sooner or later. On the fusor subject somewhere in another thread I had mentioned building a neutron generator to
test my neutron detector, and it was for fusor experiments that I did so. This is something which is within reach of the lone experimenter.
I believe you may produce them playing around with CO2 lasers and pulsed discharges, which is within the realm of being possible for the lone mad
scientist. As to propulsion the scale matters here and I am not sure you would be able to produce such power levels in a home setting. Which makes it
all the more imperitive one of us does, nothing can get a good mad scientist down!
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FPMAGEL
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A little static engine, if someone can find the funds
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Quince
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Sigh...
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Marvin
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The primary limit for chemical rockets is very simply derived from the energy they contain divided by the mass contained in. No amount of rearanging
deckchairs is going to significantly change the specific thrust.
"most of the energy is wasted by not exhausting the fuel at a very high speed, not to mention the tons of unused thermal energy left in the
exhaust. "
There is no thermal energy wasted in a conventional chemical rocket exhaust. The higher the speed of the exhaust the more energy is wasted not less.
You need to go over the theory again Quince. If you found some way to remove some of the energy from the exhaust after release and return it to the
engine this would involve increasing effective exhaust mass as reaction mass (your aparatus gets furthur away from the rocket) or slowing the rocket
down. You cant cheat conservation of momentum and your thermal energy is your momentum.
We will always throw reaction mass out the back short of using antimatter as fuel. Aside from the huge gains in thrust for a given energy spent fuel
is waste. The best you can do with a nuclear powered vehicle would be to eject the fission products out the back at the same energy they have
resulting from fission. cf chemical rockets. No amount of extracting that energy, converting to electric and then enhancing the output somehow is
going to improve that specific impulse.
ITER, even if it works is not even a power station. Even if power stations with reasonable efficiancy can be built we will certainly never see a
fusion powered rocket leave the earth. It would simply be too big even if all existing designs wern't far too heavy for the energy they produce,
which they are of course. Fusion is inherently a low density effect compaired to fission short of actually using hydrogen bombs.
The plasma engine is a waste of time for all practical purposes. Assuming you can build a rocket that gets the maximum thrust they quote. Assuming
you can get the maximum specific impulse they quote for that thurst and it all works, in other words assuming you can actually do what they are
dreaming about..... Lets assume your power supply is 10Kg, your rocket body and engine is another 10Kg and you have 5Kg of reaction mass (that forms
the plasma) then just to break even with gravity your rocket burns for only slightly more than 9mins and the power supply has to produce around 7
MEGAWATTS!
Of course this scales, so for a 25g rocket the answer is 9mins and 7Kw from a 10gram power source!
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FPMAGEL
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"There is no thermal energy wasted in a conventional chemical rocket exhaust. "
Marvin what i think they mean by that is, heat is used to make pressure to get converted to velocity, if they didn't need heat, say the energy
stored in a permagetic/fission is used to make the velocity directly, you won't waste two steps, which each step is about 80% effecency tops on
each stage.
I belive( that if a hotbox reactor like they used on apollo missions(light
weight), ionized air scramjet way, then useing magetics to speed it up, wither hot(meaning more mass/if vol doesn't change) or cold. For a
chemical rocket the MHD will take some energy from the reaction mass, but not much. Its the electrons greating a magetic difference in the copper wire
that makes the current, if you can send the current the same dierction is the flow, then move it away from the ionzied gas to send it to the frount,
the M-field would have add less stopping power to the ionized gas.
I hope you can follow, because I've just confused myself.
[Edited on 18-10-2005 by FPMAGEL]
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Quince
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| Quote: | Originally posted by Marvin
Fusion is inherently a low density effect compaired to fission short of actually using hydrogen bombs. |
What makes low density inherent in the effect? I can only see that it appears inherent in the fuel due to the use of light elements instead of heavy
ones. But that can be dealt by, say, discretizing the thrust into pulses from frozen pellets. They are still not nearly as dense as a heavy
radioactive metal, but for the same mass produce more energy. So no, you don't need hydrogen bombs -- I wouldn't call pellets bombs as
fusion is started by bombarding from an external source. This whole inherent low density thing needs more elaboration from you.
As for throwing the fission products out the back, why not throw fusion products out? Less mass for the same energy, volume would not be much of an
issue in space; use frozen heavy water as a source of hydrogen isotopes -- not much worry about micrometeorite impacts on the ice (make a good shield
for the rest of the vessel, in fact) and doesn't need to be covered even, just sprayed with a reflective paint; and sure, the oxygen doesn't
contribute nuclear energy, but makes fine reaction mass.
Saying we'll never see fusion rockets is contrary to all the scientists doing research in nuclear propulsion. So who do we believe, an anonymous
poster here, or the scientists that published papers say in section 14.01 in this conference, http://www3.inspi.ufl.edu/space/program/index.html
(not to mention the numerous that didn't make it into this years, with abstracts here http://www3.inspi.ufl.edu/space/program/abstracts/ ? Likewise for saying the plasma engine will never be practical.
[Edited on 18-10-2005 by Quince]
[Edited on 18-10-2005 by Quince]
[Edited on 18-10-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Marvin
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"This whole inherent low density thing needs more elaboration from you. "
The only attempts getting even slightly close to breakeven have been in magnetic confinement plasma systems. Even if everything goes flawlessly, and
history is against this, we wont see a power reactor running for a good 20 years. It will be massive. Making a rocket is much harder. Pellet
systems we are generally told are a more recent technology, we are also told they not well understood. This is of course a lie, the mechanism is
totally identical with the thermonuke method and various military goverments have understood this, and built highly detailed models for it over the
last 50 years or so. Given the low efficiancy of hydrogen bombs generally its rather unsurprising a much smaller version would be next to impossible
to make work.
"I wouldn't call pellets bombs as fusion is started by bombarding from an external source."
Just as it is in a nuke, so why isnt it a bomb?
"As for throwing the fission products out the back, why not throw fusion products out? "
For fission products you only need to do fission.
"the oxygen doesn't contribute nuclear energy, but makes fine reaction mass"
Basic mistake. As Ive said before you need to review the physics of rockets.
"Saying we'll never see fusion rockets is contrary to all the scientists doing research in nuclear propulsion."
Much research is done on things that arn't possible with current technology. Thats often the point. Much of this becomes obsolete before its
ever useful, and much turns out to be impractical or impossible even in the long run. How big a fusion rocket will need to be and how long after
I'm dead they will happen is anyones guess. I am not saying a fusion rocket will never be built, but I am quite sure we will all be long dead by
the time it does. Fusion has been '25 years away' according to the best scientists in the field for the last 60 years. It is still 25
years away according to the best scientists in the field, thats just for a power station.
"So who do we believe, an anonymous poster here"
... or another anonymous poster here with no grasp of basic rocket physics let alone fusion quoting abstracts from the 'open your mind' end
of conference fodder designed to promote nuclear power in space.
The fusion rocket in the conference abstract does not actually work. Its an untested and in many ways questionable modification to a basic fusion
system design that does not work either and is also too heavy. The point of the idea is not to say 'Ive designed a fusion rocket, give me the
money to build it' its an excuse to point out how wonderful it would be if it did work, and how much easier space travel would be if you can make
it work.
The abstracts link btw does not work even when the extra chars are removed.
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Quince
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Link has been fixed.
I emailed the main author of 1146 (the one @cern.ch) asking for the full text, and hoping to get a comment on his view of the practicality of a fusion
engine. It may be in vain, given that I actually referenced this thread, but I figure by the time I email all the authors someone will respond...
BTW, I wasn't trying to insult you, I was just pointing out that when conflicting general conclusions are presented from various sides without
exposing all details of the argument, an appeal to the bigger expert is the logical action for a non-expert. Referring to variouis research papers as
'fodder' doesn't do much for your argument, by the way.
[Edited on 18-10-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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mick
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mick
[Edited on 19-10-2005 by mick]
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Twospoons
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| Quote: | Originally posted by Marvin
The plasma engine is a waste of time for all practical purposes. |
I'd qualify that by adding " if you have to carry your power source with you".
The plasma launch engine is a very good idea if the launch power can be supplied from the ground via laser or microwave beams. You gain in two ways -
not having to carry a heavy power source, and having a vast source of energy available, making efficiency less of an issue. IIRC a small laser based
system has been demonstrated.
[Edited on 18-10-2005 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
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uber luminal
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you would still have to carry fuel with you, even if the power source was transmitted to the vehicle. Plasma isn't magic. You still need to
ionize something and eject something to create force. Or did you plan to pull this fuel source out of the air? in which case, you would then have to
find some source to ionize if you didnt have air.
I imagine air would play havoc on any parts that were not made of stable ceramics.
Or am I totally reading into this the wrong way?
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Twospoons
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Obviously, once out of the atmosphere, you need your own supply of ejection mass, but if you can entrain, ionise and expel air then thats a huge
saving in lift-off weight. Thats why there's so much interest in the SCRAMJET, as it initially uses atmospheric oxygen, saving oxidiser weight.
The laser system I mentjioned does use air as ejection mass.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Quince
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Also, I'm wondering what assumptions Marvin is making about the type of fusion reactor to be used. I can agree that anything like an ITER-type
Tokamak looks to be too big, but there are a number of other designs that theoretically should work. For example, "Fusion Reactors Based on
Colliding Beams in a Field Reversed Configuration Plasma"; I've seen an estimate of a 20x10 m for a 100 MW reactor.
Also, http://fusion.ps.uci.edu/artan/artan.html
[Edited on 20-10-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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FPMAGEL
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"I imagine air would play havoc on any parts that were not made of stable ceramics. "
Nasa came into problems with Nitric acid being produced, they had a ark to make it easyer to light the fuel.
Delta V to escape earth is about 5.7. To escape the solar system is 7.5. So a saturn5 fired from syn orbit using cheimcal rockets will leave the solar
system, but a 20 year trip to the nearest star 4LY is along time.
I had a look at the link above, and if I understand right they are going to convert 100,000C & speed of light to 1,000,000C and 100k/p/s using a
venture tube or theory. Thats the one to go, you don't need the large confinement, and even if it is not 100% convertion it(not 1atm when
leaving, but high V) it will still make lots of power.
Has anyone else got ideas(yours,somone elses). Once you know were you are heading you can get there.Thats the problem with Nasa, there budget is 1
billion one year 300 million the next, not to mention they could have build somthing 6.4 times the size of ISS if they sent sheets of Al 1m/1m/3cm up
there then welded them into a anti gravity circle thingy. 100 tons , damn you could build a large building. O well i hope they don't quiet there
day job.
[Edited on 21-10-2005 by FPMAGEL]
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