h a l f b a k e r yRecalculations place it at 0.4999.
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Helium3 is considered an ideal type of fuel for nuclear fusion but it is rarely found on earth. Some proposals have been to mine it from the lunar soil, which has been bombarded with the solar wind for billions of years. The difficulty of this idea was pointed to by Robert Zubrin who discussed the costs
of sending a ship to the moon, mining the materials, and sending them back to earth.
But there is another possibility that would elleviate most of the propulsion required to get out of the earth's and the moon's gravity well by placing most of the necessary infrastructure in space and mining the solar wind itself.
This could be a completely automated and mostly solar powered system. A series of probes that use solar sails align their sails at an angle to the sun that slows their orbital velocity, causing them to drop in closer to the sun.
The closer they get, the more densely concentrated the solar wind and thus the He3 particles. The power being recieved from the sun at this range would be significantly higher, powering a laser that ionizes the He3 particles and a magnetic scoop that gathers them into a receptacle.
Once fully filled, the solar sails are realigned to speed up the orbital velocity so that the probes move out from the sun and ultimately rejoin the earth's orbit. The receptacles, outfitted with wings, are jettisoned, re-enter the atmosphere and glide in to a space center just like the Shuttle does now.
Finaly, the remaining portion of the probe docs with another receptacle that was launched into orbit prior to the probes return, and heads back to the sun. To save on propellant, the receptacle could serve as its own rocket stage. It is filled with chemical propellant, which it expells in order to reach orbit. Then it is refilled with He3 from the solar wind and brought back to earth.
One round trip could take quite some time. Maybe several years. But if you launch hundreds of them at regularily spaced time intervals, payloads of He3 would be arriving every day.
(Bussard) Ram Scoop Devices
http://www.itsf.org...chure/ramscoop.html
[phoenix, Oct 04 2004, last modified Oct 21 2004]
³He Enhancements at Interplanetary Shocks
http://www.srl.calt...News/ACENews44.html
Borrow a magnetic scoop from Ma Nature [lurch, Oct 04 2004, last modified Oct 21 2004]
M2P2
http://en.wikipedia...c_plasma_propulsion
This plasma solar sail gets bigger the farther you get from the sun, so that the total amount of solar wind intercepted is always a constant for a given amount of electrical energy input to the plasma sail. [Khous, May 12 2007]
[link]
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Any numbers on how much He3 goes flying past us, and how much you would need for sustainable nuclear fusion? |
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Oh, that's the next-generation Hummer. |
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Did you know if you inhale He3 you can talk just like a martian? Keep that in mind if you want to crack up Ground Control on the return trip. |
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Great gag, until they blast you to nano-bits, thinking you actually are a martian. |
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I thought solar winds always blew away from the sun... |
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Gathering He3 from the solar wind at our vicinity from the sun would require a much larger magnetic scoop to get the same amount of material in the same amount of time. |
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Along the lines of one hare-brained scheme deserving another:
Suck in the gases available in the solar wind. Ionize and then accelerate them across a voltage differential (solar-powered ion engine) and then pass the output through a magnetic field. This forms a mass spectrometer, allowing you to selectively re-gather the He3 from the exhaust stream. |
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While this idea might very well work, the part about Zubrin is kinda sketchy. I'm not too sure that I would put too much credibility in anything he has to say about the moon, since he has a vested interest in discouraging exploration of it. His goal is Mars. Anything that might take funding away from Mars exploration is a Bad Thing, in his books. Hence, he has a likely bias. |
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Though, I haven't read the article in question, so I really can't say much about it. However, you've suggested a valid way to work around any difficulties that we might discover on the moon. You get bunnified for thinking outside of the Earth's gravittional well/box thingy. |
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It doesn't have to be just helium-3; ALL different types of atoms that exist on the Sun's surface get blown off, joining the solar wind. With solar-sail-mounted and solar-powered mass-spectosorters, we can get oxygen and hydrogen for water, carbon, nitrogen, phosphorus, and everything else needed to sustain life in space. ALSO, and mostly, we can accumulate and liquefy and tank up nice large quantities of ordinary hydrogen, for ordinary chemical-rocket fuel. Shove those toward the Moon, or any Earth-crossing asteroid, and set up solar-powered mining facilities to extract oxygen (50% of the Earth's crust, and presumably a not-too-dissimilar percentage of other bodies, is oxygen), thereby obtaining the other half of ordinary chemical rocket fuel. (I've been carrying around the idea of getting ordinary hydrogen form the solar wind for some years, but don't recall if I got it from somewhere else.) |
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The advantage of the helium-3/deuterium reaction over other fusion reactions is that the yield is large, and it produces no neutrons! This means all the products of the reaction (1 helium-4 ion, 1 proton) are controllable by magnetic fields, and can be safely guided away. |
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If you read the Daedalus report (a series of articles about building an interstellar probe), published by the British Interplanetary Society, they considered three ways of getting hold of helium-3 (deuterium can be extracted from seawater). They were breeder reactors, from the surface of the moon, or from the atmosphere of Jupiter. Fantastically, the Jupiter idea won over the others. However, since the report was written in the 70's, a rethink may be in order. |
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What if a receptacle missed it's target or burned up in the atmosphere? You'd have lots of radioactive gas floating around. |
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If I had a penny for every million bucks you'd lose bringing this to fruition, I'd retire a very happy man. |
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<yoda>Not yours the sun. Everyone's the sun.</yoda> |
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Just did a little research and found that passively collecting material from the sun wouldn't be that efficient. The sun looses 10 million tons of raw material per year. Or 27397 tons per day. We could only collect a fraction of a fraction of that by passively sifting through the solar wind. You'd have to invent machines that could go right into the sun with huge magnetic scoops to harness material fast enough to be feasable. |
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[Anarch], remember that most of the Solar Wind particles leaving the Sun are electrically charged, and so can be reaped by appropriate large-scale electric or magnetic fields (and Space makes it easy for us to build on the large scale). |
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So, to return to the basic premise, how
much better is 3He than other possible
fusion fuels? Is it likely that we'd get a
reactor working with 3He but be unable to
get something running (within the
following decade) for a hydrogen isotope
or 4He? |
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The beauty of He3 fusion is that it doesn't produce neutrons, and therefore doesn't cause the structure of your reactor to become radioactive. |
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Unfortunately the energy barrier to overcome is much higher than that for deuterium-tritium fusion, making it much more difficult to run a controlled reaction - and the D-T reaction is already hard enough that it's uncertain whether it's a practicable possibility to make a power reactor based on it at all. |
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4He isn't a fusion fuel at all - it's the end-product of fusion reactions (unless you're a supernova). |
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