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Nuclear fusion

Posted by: Dr_Keith_H - Sun Jun 06, 2004 1:26 pm
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Nuclear fusion 
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Post Nuclear fusion   Posted on: Sun Jun 06, 2004 1:26 pm
Nuclear Fusion
n54 wrote:
fuel on the moon (helium-3)
http://www.space.com/scienceastronomy/h ... 00630.html

this is fuel for fusion reactors and to use it for propulsion (back to earth or similar "short" trips) i think the following setup would be best:
- extraction plant
- fusion plant
- electromagnetic "rail gun" launch of the vessel from the moon

how small could one make those 3 (4 counting the vessel) parts? if one could make them really small, launching them privately might be possible as a proof of concept kind of thing (but i think the research needed requires a huge budget)

the problem is that the moons environment is extremely fragile which i think poses some extra challenges:
http://www.marsinstitute.info/rd/facult ... v06-1.html

and do we want to use it all up or use it at a sustainable rate? note that it doesn't take much activity to "plug the well" so to speak

fuel on mars: http://www.marssociety.com/about/faq.asp#in_situ_fuel

there's plenty of good stuff on this subject here (although old):
http://www.marsinstitute.info/rd/facult ... tr-lv.html

their main page:
http://www.marsinstitute.info/rd/faculty/dportree/rtr/



interesting links ... but I haven't read anything there that suggests anyone has gotten beyond the drawing board ... still, it's all food for thought ...(later) ... I went looking for more stuff, this one by Pacific Northwest Labs is good, but it looks like its still only a design (an old one too, from 2000)

http://www.pnl.gov/microcats/aboutus/pu ... Imret4.pdf

I also found out about an experiment (in-situ propellent production) that was supposed to fly on something called the Mars Surveyor Lander (??) back in 2001 but was postponed ... indefinitely is my guess.

http://powerweb.grc.nasa.gov/pvsee/publ ... _LPSC.html

Can anyone find anything else? By which I mean actual ISPP experiments, not just drawing-board design (of which n54 has found a lot).

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Post    Posted on: Sun Jun 06, 2004 1:42 pm
n54 wrote:
fuel on the moon (helium-3)
http://www.space.com/scienceastronomy/helium3_000630.html

this is fuel for fusion reactors and to use it for propulsion (back to earth or similar "short" trips) i think the following setup would be best:
- extraction plant
- fusion plant
- electromagnetic "rail gun" launch of the vessel from the moon

how small could one make those 3 (4 counting the vessel) parts? if one could make them really small, launching them privately might be possible as a proof of concept kind of thing (but i think the research needed requires a huge budget)


For one thing, you can ditch the railgun. Don't need it. Fill up on He-3, build the fusion drive directly into the ship itself, and (given enough time), you can hit 20% of lightspeed -- given *LOTS* of time, unless you want your passengers to turn into smears of strawberry jam on the floor in the meantime. A fusion drive is basically the goal of any interplanetary vehicle designer, as it uses very little fuel, has incredible thrust and specific impulse, and what may as well be an unlimited top speed (since you'll never hit it anytime soon). So it approaches the Ultimate Engine (zero fuel, infinite thrust and Isp, infinite top speed) pretty closely for our technology.

And it's coming to a spaceport near you sometime in the next couple decades! Plenty of folks are trying to come up with an energy-producing fusion reactor. They've already got self-sustaining fusion reactors (ones that don't require any energy input), which is all that any spacecraft needs. So team the fusion drive up with an energy-producing fission reactor to help kickstart it, and you're set. Fission reactors aren't nearly as hard to handle in space as they are on Earth:
1) No environmental concerns
2) Since you've already got heavy radiation shielding on the outside of the vehicle, you can basically mount the nuclear pile on the outside (with sufficient armor to keep it from getting splattered all over your hull by the next micrometeorite)
3) If you design the rad shielding right, any meltdown will be funneled away from your ship, thus preventing you from being harmed (although you won't want to shut down your fusion drive unless you feel like coasting for the next couple AU)
4) Dumping the spent fuel is no problem -- just let go of it in such a way that it will fall into the Sun

It basically amounts to this: get yourself a fusion-powered interplanetary ship, be willing to be a little uncomfortable with some extra acceleration and to burn fuel at a slightly prodigious rate, and you can get to Mars in a few hours. Yeah, that's right. A. Few. Hours. As in less than two days.


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Post    Posted on: Sun Jun 06, 2004 2:03 pm
spacecowboy wrote:
Plenty of folks are trying to come up with an energy-producing fusion reactor.

This statement is, without doubt, true.
Quote:
They've already got self-sustaining fusion reactors (ones that don't require any energy input), which is all that any spacecraft needs.

Wow, that sounds unbelievably exciting ... who are "they" and where can I find information on their self-sustaining fusion reactor which don't require any energy input (if that is so, then shouldn't there be a measureable output?).

Dang it all spacecowboy, could you possibly mean instead that engineers and scientists have developed reactors (JET, MAST, etc) that can sustain fusion briefly?

I don't think they've even started building ITER yet ...

Did i miss something?

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Post    Posted on: Sun Jun 06, 2004 2:18 pm
hmm i think you completely missed the point about the moon environment being extremely fragile

use fusion drives for takeoff from the moon and you're in danger of destroying "the well", from the link:
Quote:
...owing to leakage and rocket exhaust, each Apollo mission doubled the mass of the moon's atmosphere. The mass dropped to normal after a month, so Vondrak asserts that "small lunar colonies" and modest mining "present no lasting hazard to the lunar environment." If, however, more "vigorous" human activity pumps up the atmospheric mass to one billion metric tons, solar wind and ultraviolet will be able to ionize only its outermost fringe. The thin atmosphere will then persist for centuries even if no more gas is added.

so a railgun system would be beneficial as it would allow for a lot more launches (the less impact the launches have the more you can have of them or other polluting activities while maintaining the balance)

i view the moon as a helium-3 generator in the sky and think we should be meticulous in maintining it as such as thats a great long-term resource

it's a serious matter (pun not intended) noone seems to pay any attention to :(

i guess what will happen is that the moon will become pretty much useless concerning helium-3 when we've come so far as establishing a permanent base there


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Post    Posted on: Sun Jun 06, 2004 2:21 pm
*grr* another guest post by me lol

well i guess you knew it was me anyway :D


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Post    Posted on: Sun Jun 06, 2004 2:45 pm
I think fusion will be the way to go for some time as the benefits are HUGE. The energy produced is vast and overcomes the contamination problem if a craft fails (so environmentalists will be happy!).

Dr_Kieth_H, you are right, ITER has not been built yet (there's still an arguemnent over where it should be!) and sustained fusion will only probably be achieved when it comes on line in 10-15 years.

It's important to note however that Helium-3 is not the ONLY fuel that can be used for fusion. ITER is using Deuterium and Tritium, both isotopes of Hydrogen. It may not be necessary to take a hop to the moon!


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Post    Posted on: Sun Jun 06, 2004 6:11 pm
Nova wrote:
I think fusion will be the way to go for some time as the benefits are HUGE. The energy produced is vast and overcomes the contamination problem if a craft fails (so environmentalists will be happy!).

i doubt environmentalists will be happy about fusion as it too produces radioactivity (yes, less than fission but still some) and that's not even concidering any failures (i hope you're not proposing using this technology on a rocket inside the earths atmosphere or in orbit)

Nova wrote:
It's important to note however that Helium-3 is not the ONLY fuel that can be used for fusion. ITER is using Deuterium and Tritium, both isotopes of Hydrogen. It may not be necessary to take a hop to the moon!

yes, but remember that ITER isn't built yet :D

i noticed one of the links (http://www.marsinstitute.info/rd/faculty/dportree/rtr/lv06-1.html) saying there's about 50 metric tons of helium-3 on the moon, and another of the links (http://www.space.com/scienceastronomy/helium3_000630.html) saying 25 tons (1 space shuttle cargo bay hold so i'm gussing it will be metric) is about enough to cover the us energy consumption for a year

i'm not too sure if the above numbers still hold true but when we establish a presence on the moon let's spend it wisely to ensure that it continues to be able to soak up helium-3 (i.e. by avoiding fusion drives freeing trapped gas in the lunar soil at takeoff, or similar)


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Post    Posted on: Sun Jun 06, 2004 7:57 pm
yes you are right that the process does create SLIGHLY radioactive products, but certainly not anywhere near fission levels, they're almost non existant. This radiactive waste has such a short half-life that it's hardly worth calling it radioactive! Think about it, the products formed are so small compared to other elements that they can't radioactively break down that much anyway.

And yes I am considering this technology could be used at least in orbit. There's no reason why not, remember there is far more radiation in orbit than any amount of fusion drives could produce and far more deadly, THE VAN ALLEN BELTS. To keep concerned people happy though i'm sure if it required it there would be a ban on using such a propulsion method on the moon to retain the h3.

I know the ITER isn't built yet, I said it! but I put it back to you, has a sustainable Helium-3 reactor been built yet? :) ITER will be built before that.

I don't know if the figures for the amounts of h3 are right (unfortunately I can't get there just yet :D ) but it sounds right about the amount of energy produced from a ton, even probably for more than a year. I did say that fusion produces a hell of a lot of energy.

I don't know if you have noticed but there are two issues here, using fusion for POWER and using it for PROPULSION. h3 would be great for POWER production but more widely available materials ie Dueterium and Tritium would be more applicable to widespread use in PROPULSION.


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Post    Posted on: Sun Jun 06, 2004 8:15 pm
i was thinking earth orbit (my mistake) and as to the orbit i'm not worried about any radiation but rather what happens if it goes out of orbit in an uncontrolled manner (i.e. down)

has any stable fusion reactor been built yet? (not talking seconds or minutes)

and i think there are more than two issues here :wink: j/k

does anyone know the percentages of alpha, beta and gamma radiation from fusion? (i'm thinking in relation to each other) btw i have a hard time believing that for example the radiation shielding on a vessle using a fusion drive wouldn't become highly radioactive over a fairly short period of time


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Post    Posted on: Sun Jun 06, 2004 8:51 pm
I'll keep it brief this time!

Answer 1: ITER will be the first, hopefully.

Answer 2: Fusion mostly produces free neutrons as radiation, not any of the "normal" radiation. This does have it's problems i.e. material distortion but that is being adressed in the manufacture of tokamaks.


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Post    Posted on: Sun Jun 06, 2004 11:01 pm
interesting but i had to start checking up on this (as fusion is what happens in a hydrogen bomb i just couldn't match what you say with what i think is right) and found this:
Quote:
Fusion begins with the combination of four hydrogen-1 nuclei to create two hydrogen-2 nuclei. As a result, two positrons (positive electrons) and two neutrinos are released. These two hydrogen-2 nuclei, together with another two hydrogen-1 nuclei, form two helium-3 nuclei and release gamma radiation

at http://www.fact-index.com/s/so/solar_radiation.html

now gamma rays to my knowledge is the worst kind of radiation there is... not only is it much much harder to shield than alpha or beta radiation but it's also (unless my memory fails me) both the longest lasting of the radiation types as well as causing secondary alpha, beta and gamma radiation in surrounding material

ok i know we're way off topic here lol :D

it's just interesting and a long time since i had anything to do with radiation, so if anybody wants to enlighten my ignorance with some specific wellwritten links please do :D


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Post    Posted on: Mon Jun 07, 2004 12:27 am
I know were going a little off topic but i'd better say this to clear up the confusion before the thread moves on.

The quote you made is of Stellar fusion, that is different from the type of fusion being attempted commercially and obviously has different by-products. Of course Stellar fusion produces a lot of radiation, think of the sun!

There are in fact around 10 types of fusion known so far, I can assure you that what I said is right for the commercial fusion, known as D-T fusion. Come on, you don't think that the people chosing a clean energy of the future are going to use the most polluting (and dangerous) form of fusion do you? They chose D-T fusion as it shows the most promise in being clean and easy to to produce.


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Post    Posted on: Mon Jun 07, 2004 1:12 am
Nova wrote:
I know were going a little off topic but i'd better say this to clear up the confusion before the thread moves on.

The quote you made is of Stellar fusion, that is different from the type of fusion being attempted commercially and obviously has different by-products. Of course Stellar fusion produces a lot of radiation, think of the sun!

There are in fact around 10 types of fusion known so far, I can assure you that what I said is right for the commercial fusion, known as D-T fusion. Come on, you don't think that the people chosing a clean energy of the future are going to use the most polluting (and dangerous) form of fusion do you? They chose D-T fusion as it shows the most promise in being clean and easy to to produce.


Au contraire. (please excuse any spelling/punctuation errors)

http://www.itsf.org/brochure/fusion.html

http://www.daviddarling.info/encyclopedia/F/fusion.html

Even better:
http://www.daviddarling.info/encycloped ... usion.html

http://www.fact-index.com/f/fu/fusion_rocket.html

http://www.nationmaster.com/encyclopedia/Fusion-rocket

http://www.newscientist.com/news/news.jsp?id=ns99993294

***

Deuterium-Tritium ("D-T" written out) fusion is the one that exists in the sun and, when used correctly, produces negligible amounts of harmful EM radiation. It is also the most efficient mass-to-energy conversion known to mankind, with about a 20% conversion factor -- if I remember correctly, fission is about 3%.

http://www.spectrum.ieee.org/WEBONLY/pu ... epow3.html

The above is an article in a publication from the Institute of Electrical and Electronics Engineers ( http://www.ieee.org/portal/index.jsp?pa ... eneric.xsl ), an eminently respectable organization. ITER is not yet completely planned out, and I stand corrected on my rash claim that self-sustaining fusion reactors had been built. Successful sustained fusion reactions have kept going for months at a time (this *is* a fact; I remember watching a special about a university that operated one).

Radiation from Deuterium-Tritium fusion is negligible, not by any standards, period. The Sun produces as much radiation as it does because of its sheer mass: if you were to dump all the planets, the asteroids, and the entire Kuiper belt, you might enlarge the Sun's diameter by a quarter inch. Think about that for a moment. The other byproducts are harmless -- nontoxic isotopes of helium and hydrogen. What is with you people and radiation? You can mount a slab of plutonium on the outside of an interplanetary vessel and not even notice it except for the mass. If it weren't for and the cost, we likely would: it would give excellent protection against the vastly more potent solar wind. Fusion reactions do not produce noteable radiation.

All together now: FUSION REACTIONS DO NOT PRODUCE NOTEABLE RADIATION.

Nova: you're right. Fusion does produce a hellacious amount of energy. I remember reading somewhere that a single bucket of seawater contains enough deuterium and tritium to power a decent-sized city, assuming 100% reactivity and conversion. And yes, it does occur naturally on Earth, and in large amounts -- just not in large percentages, like it does on the Moon.

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Post    Posted on: Mon Jun 07, 2004 2:47 am
Au contraire, mon ami

This seems to be a common misconception. D-T fusion IS NOT responsible for the fusion reactions in a star. This confusion occurs when articles state the uses of fusion power i.e. commercial and then links this to fusion in a star.

the actual process called the proton-proton chain and i can tell you that the products DO account for the radiation given off by a star on it's own!

Here's a site i found that explains it (nice graphic too):
http://library.thinkquest.org/17940/texts/ppcno_cycles/ppcno_cycles.html
(I've only got one link, i feel so inadequate now!)

See how many gamma rays are produced! Boy does THIS fusion reaction produce radiation.

so all together now: SOME FUSION REACTIONS CAN AND DO PRODUCE RADIATION

Even through this, at least someone agrees with me that radiation is not going to be much of a problem for D-T reactors.


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Post    Posted on: Mon Jun 07, 2004 1:58 pm
interesting debate

first of all i would like to state again that my main worry for earth-orbits is any accidents involving crashes (i state it again as it seems to be lost in the debate for some weird reason).

and for the moon my worry is "poisoning the well" not by radiation but by the force from a ground launch using this method displacing huge amounts of helium-3 into space as well as creating a "temporary" (or not, depending) atmosphere which both makes helium-3 extraction a more laborious process as well as preventing the "soaking up" of more helium-3 by the moon

for interplanetary/space propulsion i have no objections to any nuclear propulsion types (although i think future technology will make such brute force unneccesary, but that's for another thread and another time)

at least some fusion reactions does create enormous amounts of radiation, if you think otherwise read up on hydrogen bombs

as to neutrons it could be an idea to look into neutron bombs...

in one of the links they state that fusing protons and boron 11 produces neither gamma nor neutrons, and that sounds swell for energy production but i note that the drive designs focus on the newtonian forces from ejected charged particles and don't see how boron 11 & protons would be applicable for such designs. some of the mentioned designs focus on ejecting alpha particles (the same as alpha radiation) and that sounds promising for space but i still doubt it will ever be allowed inside the atmosphere for security reasons.

lastly: reactors, i'd choose a fusion reactor over a fission reactor anytime (who wouldn't?) and i don't see how reactors have much (if anything) to do with propulsion so why don't we drop that part so as to make this more space-related?


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