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Fusion For Space Propulsion

Posted: Fri May 09, 2008 4:38 pm
by MSimon

Re: Fusion For Soace Propulsion

Posted: Fri May 09, 2008 8:51 pm
by djolds1


As a LONG TERM fuel source I do prefer the DHe3 fuel cycle to pB11. Easier to access in a space based society, capable of providing millions of years of fuel for civilization in this solar system alone.

Much higher neutronicity than pB11, yes, but still minuscule next to DT and DD. 2x the energy output of pB11 in charged particle products for the primary DHe3 fuel cycle. And the technical requirements for the DHe3 cycle BFR are lower than those of the pB11 cycle BFR. Possibly useful when you switch over to production models.

And assuming we never crack gravity/field propulsion, Fusion pulse is ideal for travel beyond this system, and large stocks of DHe3 easier to obtain and justify expending for interstellar exploration and colonization than pB11. Higher energy content, easier acquisition assuming a mature space based economy.

However, I'd really prefer to crack field propulsion. :D

Posted: Wed May 21, 2008 11:37 am
by Keegan
Helium 3 is nice but you are still going to get some nasty high energy neutrons from unavoidable DD reactions that are going to occur. These present some serious problems. Especially in space flight.

The polywell is what it is today because of Dr B's quest to design a reactor to run p + B11. It is for all purposes built around this fuel, so we might as well use it.

I almost feel like posting something big on NASA spaceflight. What has me really excited is if we coat a p + B11 reactor wall with carbon (diamond film) It will not only effectively protect the reactor walls, but will generate oxygen. Something handy for spaceflight i believe 8)

Posted: Wed May 21, 2008 11:53 am
by vernes
Keegan wrote:The polywell is what it is today because of Dr B's quest to design a reactor to run p + B11. It is for all purposes built around this fuel, so we might as well use it.
But for spaceflight, you get more eV from He and it requires less energy to generate fusion conditions.

I'm guessing they rather go for that and just put some more effort in shielding.
Perhaps putting the engine far away from crew and cargo?

reactor,shielding,cargo+crew
-O
>O##########=D
-O

Posted: Wed May 21, 2008 12:09 pm
by Keegan
^ Vernes, when i talk about neutrons im not reffereing to the crew. Im talking about it wearing out the reactor. DD Tokamaks are uneconomical and have short lifespans cause of the neutron / first wall problem. You cant exactly repair a reactor in space. Alpha particles from p + B11 are different. Im currently integrating a solution.

Posted: Wed May 21, 2008 2:21 pm
by vernes
Keegan, you're right. Was was overlooking that fact.

Posted: Thu May 22, 2008 7:12 am
by djolds1
Keegan wrote:Helium 3 is nice but you are still going to get some nasty high energy neutrons from unavoidable DD reactions that are going to occur. These present some serious problems. Especially in space flight.


Neutronicity from DHe3 is not too difficult to deal with. And once in space in a significant way, the issue is what fuels are easiest to access and provide the highest return. Also, significant levels of radiation are present everywhere in space. Dealing with it is simply the cost of living.

Keegan wrote:The polywell is what it is today because of Dr B's quest to design a reactor to run p + B11. It is for all purposes built around this fuel, so we might as well use it.


No disagreement. An elegant concept that looks to be well on the way to realization. Certainly for the first several decades to century the pB11 cycle will be dominant. But once infrastructure in space is well along, the availability of fuels, power densities of output and lower necessary reactor efficiencies for the DHe3 cycle are attractive.

Keegan wrote:I almost feel like posting something big on NASA spaceflight. What has me really excited is if we coat a p + B11 reactor wall with carbon (diamond film) It will not only effectively protect the reactor walls, but will generate oxygen. Something handy for spaceflight i believe 8)


Interesting. Thanks.

Duane

Posted: Thu May 22, 2008 3:46 pm
by derg
I believe Dr. Bussard estimated it would take 5-7 years at $10 B to build after (and assuming) positive Polywell tests. Does that sound about right?

Posted: Fri May 23, 2008 5:16 am
by djolds1
derg wrote:I believe Dr. Bussard estimated it would take 5-7 years at $10 B to build after (and assuming) positive Polywell tests. Does that sound about right?


Using current North Atlantic lawfare-safe zilch-risk engineering practices, yes. Using Chinese/Russian/Indian/1950s US risk-tolerant engineering practices, 1.5 GUSD.

Duane

Posted: Fri May 23, 2008 11:30 am
by derg
djolds1 wrote:1.5 GUSD.



What does this mean?

Posted: Fri May 23, 2008 12:31 pm
by tonybarry
I think Duane means 1.5 x 10 ^ 9 US dollars. (a GigaDollar).

Regards,
Tony Barry

Posted: Fri May 23, 2008 4:43 pm
by derg
Well if what djolds says is true and it turns out that time is a function of cost, then that should put it within the 18 month range of private sector investment. The private sector probably does more risk-tolerant engineering these days, so that might be the way to go.

Posted: Sat May 24, 2008 4:39 am
by djolds1
tonybarry wrote:I think Duane means 1.5 x 10 ^ 9 US dollars. (a GigaDollar).

Regards,
Tony Barry


Yup.

Giga-USD, also
Mega-USD (MUSD)
Kilo-USD (KUSD), and
Tera-USD (TUSD).

IIRC, the current US GDP is 15 TUSD.