>> Regardless of whether the case is true r not for "conventional" 
>> energy
>> sources, nuclear fusion utterly romps home, IF you can do it and IF
>> you can fuel it. Lunar Helium (deposited from the sun via the solar
>> wind), while still not proven, would be a sustainable source of 
>> 'fuel'
>> (at least for the next billion years or two).

> We have plenty of fusion "fuel" right here on earth.  A surprisingly 
> large
> fraction (about 1/4500) of hydrogen atoms in naturally occurring 
> surface
> water is actually deuterium (an extra neutron).  This is the 
> substance that
> nuclear fusion reactor research is aiming to use.

Deuterium is indeed is one of the several components that can be used 
in fusion reactions, but has it's problems. Abundance is not one of 
them :-). As you note, it is freely available in all water. Water 
electrolysis will not break down deuterium based "heavy water" 
molecules and it accumulates in the cell as a byproduct. The WW2 
Germans obtained theirs from Norway where they had large hydroelectric 
resources and used electrolysis for gas generation. BUT the intended 
German use was as a moderator (neutron absorber) in a "conventioal" 
fission reactor.

HOWEVER, the other component in the most workable (for us at this 
stage) form of fusion is tritium This is a radioactive substance which 
does not occur naturally and has a half life of 10 years. It is 
commonly used in H bombs and (surprise) some luminous watch faces. It 
is in extremely short supply. It can be bred from Deuterium by slow 
neutrons so a fusion reactor could breed its own tritium in due 
course. However, while this is one of the more doable versions for a 
startup, about 80% of the energy output is as neutrons which must be 
managed by absorbtion or secondary reactions.

All fusion reactions except one produce nasty by-products which must 
be dealt with. The exception is Deuterium - He3 fusion which produces 
no undesired byproducts and whose output is able to be handled 
"easily" (relatively speaking).

        Deuterium + He3 -> He4 + a 14.7 MeV Proton.

As He4 is not radioactive and the Proton can be managed with electric 
or magnetic fields this is the gold standard for controllable 
containable fusion. But it requires far higher temperatures than some 
of the other options. Many of these produce really energetic gamma 
rays (light on steroids) which are not keen on being contained or 
directed.

Deuterium-He3 is liable to be the method of choice for space use and 
ultimately for terrestrial use. He3 is very rare on earth, being 
obtained only from nuclear reactors (or H bombs if you can run very 
very very fast). Production at present is only 10 to 20 kg/year and 
total reserves around 300 kg. However, it is believed (hoped 
earnestly, prayed that, ...) the top layer of the lunar surface is He3 
rich which has been deposited by the solar wind. (Don't you just love 
it when a plan comes together). Once we exhaust that source the 
gas-giant planets are believed to contain vast amounts of He3 from the 
(believed) original nebula that our system (is believed to have) 
condensed from. There seems to be a staged progression here :-).

Real men (and stars) use Proton-Proton fusion (or the carbon cycle for 
real heavyweights), but these are liable to be out of our class for 
the forseeable future.

Read all about Lunar He3 - The Artemis Project
Immense amounts of information.
Excellent.

        http://www.asi.org/adb/02/09/

1 kg of He3 + 2/3 kg of Deuterium yield 19 megawatt years of energy.
A He3-D reactor is inherently fail safe (as long as you are not 
standing tooooo close). No radioactivity release. No cleanup (just 
pick up the (very small) pieces). Earth's current energy needs could 
be supplied by about 50 to 100 tons/tonnes of He3/year. An entirely 
achievable amount from lunar resources IF it really exists. If the 
estimated 1,000,000 odd tons are really there that should be enough 
for 10,000 years at present energy use. If we get that long (highly 
moot) we should be very well into being able to mine the gas giants by 
then.


        RM

_______________

Desert Storm VI
Where your power may come from.
Lunar He3
Lunar solar power farms.
Material for Hydrogen fuel cells
More ...

        http://www.finetuning.com/articles/p2-970-the-moon-the-persian-gulf-of-the-21st-century.html
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