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I'd like to interject, if I may, with something alternatively nuclear called "Sonofusion" which I just hppened to stumble upon while googling New Scientist magazine.
The World's No.1 Science & Technology News Service
Stronger evidence for desktop fusion
17:45 03 March 04
NewScientist.com news service
The controversial claim that bubbles popping in a simple desktop experiment can produce nuclear fusion - the same process that powers the Sun - has been re-asserted by scientists.
In 2002, Rusi Taleyarkhan's team at Oak Ridge National Laboratory in Tennessee, US caused a storm, when it announced it could make heavy hydrogen nuclei fuse by forcing tiny bubbles in acetone to implode when blasted with sound waves - a process called sonofusion.
The result opened up the possibility of a cheap, limitless supply of energy. Yet critics were quick to point out flaws in the work, especially when a second team of researchers at Oak Ridge repeated the experiment and failed to find neutrons or radioactive tritium, the tell-tale signs for fusion.
Now Taleyarkhan, who has since moved to Purdue University in Indiana, claims he has done it again - and this time he says the evidence for desktop fusion is even stronger.
Although no one has tried repeating the latest work, Lee Riedinger, deputy director for science and technology at Oak Ridge, says that, it went through an "extraordinary level of review" before being accepted for publication by Physical Review E.
In the first experiment, Taleyarkhan and colleagues fired neutrons at a tank of chilled acetone to create tiny bubbles. The hydrogen in the acetone had been switched with deuterium, a heavier form of hydrogen with an added neutron. Blasted sound waves caused the bubbles to expand and then collapse many times.
Rusi Taleyarkhan, Purdue University
Physical Review E
The researchers argued that as the bubbles imploded, the temperature inside would rise to millions of degrees, hot enough for two deuterium nuclei to fuse together. This fusion would produce either tritium - an isotope of hydrogen - and a proton, or a helium-3 nucleus and a neutron with 2.5 million electronvolts of energy.
The team found evidence for both reactions, but other researchers pointed out discrepancies with the amount of neutrons and tritium detected, and the fact that the detector was set up to screen out 2.5 million electron volt neutrons.
Taleyarkhan says he has since revamped the equipment so that it is better at detecting neutrons. He claims the evidence for fusion is even stronger this time: the neutrons show the right energy and their levels match the amount of tritium detected.
But this may not be enough to silence critics. Larry Crum, an expert in acoustics at the University of Washington in Seattle, believes the new results lend credence to the idea of sonofusion. Yet he remains sceptical of Taleyarkhan's findings. "I still don't think anyone is going to believe it," he says.
Valerie Jamieson
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Sonic "fusion," if that is indeed what is happening in that tank, will not be practical for an engine because of the small amount of material it can fuse. It might make a fine desktop neutrino or neutron source though.
The thrust is only really a big concern on the first stage of the rocket, the upper stages' performance is governed more by the efficency of the engine and not its force. Efficency of an engine per-mass of fuel, since that is the real concern, is dependant on its specific impulse which is in turn governed mainly by the velocity of the exhaust molecules: the best chemical rockets top out at around 450sec Isp for LOX/LH2 because of the low amount of heat available and the high mass of the water molecules.
For rockets, specific heat is actually a rough measure of how efficent a fuel it is, because there are more particles to push per-mass, hence each particle is light and can achieve a very high speed that yeilds very high fuel efficency. A high specific heat isn't a bad thing, quite the opposit, it is generally speaking A Good Thing. Nuclear reactors also packs so much energy into such a light package relativly speaking, that providing the requisit energy is not a problem at all up to the limits of the reactors' materials.
Russia actually did experiment with ammonia or mixtures of ammonia and alcohols in their early NTR engines for use as a high-performance storable propellant, and they will work, but the problem is that ammonia is still quite heavy and hence you can't impart a very high velocity to its molecules (or at least the Nitrogen made by decomposition), which limited the Russian designs to around 470sec. Its possible to raise this figure, but I doubt by very much; the point is that the only fuel that would justify NTR engines is hydrogen, since you can impart a huge velocity to its light weight molecules: even Helium is awfully heavy.
NTR/Hydrogen can reach Isp of around 1,000sec in theory, more than double the efficency of any rocket, which would make it worthwhile in my opinion for a trip to Mars or large-scale flights to and from the Moon, so it is worth the expense and tiny risk... use any other fuel and we might as well be using chemical engines.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Small RTG's have proven highly reliable over years (even decades) of use, but have fairly low power output for their weight. Gas cooled and liquid cooled nuclear reactors can have very high power outputs, but are relatively unreliable on timescales of more than a few months.
Small RTG's can be strung together like batteries to yield higher outputs. The additional weight required to assemble a radiatively cooled (ultimately air cooled on the Martian surface) nuclear pile of this type may be well made up for in the increased reliability over a more compact, actively cooled reactor. Such a pile would not be subject to risk of meltdown, and need not be too much heavier than alternatives that require active cooling.
It's not nuclear power that bothers me. It's having to run your nuclear power supply so hot that you can't go near it to fix it and it melts if something goes wrong. If my powerplant breaks, I want it to just break, not send me running for my life.
I also have a question: What are the prospects for in-situ construction of a nuclear pile on Mars? What are the expected chances for finding useable radioactives on Mars?
"We go big, or we don't go." - GCNRevenger
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Regarding nuclear reactors situated initially on Mars: I've yet to read anything concerning the consequences to the virgin atmosphere due to radioactive fallout, in case of damage or malfunctioning, before containment structures are in place. Any serious thoughts or observations?
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First of all, the reactor they'll be bringing to Mars won't be very big, so the scale of any fallout will be limited if there were to be a catastrophic failure, and second the material that produces the bulk of harmful radiation doesn't last that long (Hiroshima is a lived in city again, only minimal background increase), so I don't think its a big problem... if Doc-Z's plan or Mars Semi-Direct is actually done, then you'd get in the ERV and leave without much trouble. Martian space suits will probably already be made with borated/leaded polyethylene, so the only issue would be cleaning the contaminated dust off before leaving for Earth.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Good observation, but surely long-term planning should be considered for Expedition 2, etc. E.g., Radial berm shielding within a covered nearby crater, buried (or not) depending upon what is found out regarding the ground water/brine/tundra conditions would be worth discussing, I should think, while awaiting the rover(s) stop-motion exploits to come up with some more answers. Floor or no floor? Positive or negative pressure? Means of generating em--by turbogenerator or bi-metallic junction piles. Voltage, dc, single- or three-phase ac? And then on to Solar and vertical wind-turbine generated emf tie-ins. All possibilities and combinations capable of being designed and tested-to-distruction right here on Earth.
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Well, yeah, but you don't want any of that catastrophic failure stuff.
Why use a design where that's a possibility?
"We go big, or we don't go." - GCNRevenger
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Just my point: Design for avoidance of that catastrophic stuff, and test the design alternatives here--by whatever means already deemed "safe" for underground nuclear weapons, instead of on Mars. Then make the decision yes or no for a fission reactor to be included initially. If no, then work out and test the alternatives now, as long as we have this waiting time imposed upon us by the bean counters, et al, anyway.
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[http://www.spaceref.com/news/viewpr.html?pid=13860]NASA partners with DoE Naval Reactor Program
*"The Department of Energy's (DOE) Naval Reactors (NR) Program joins NASA in its effort to investigate and develop space nuclear power and propulsion technologies for civilian applications. These activities could enable unprecedented space exploration missions and scientific return unachievable with current technology.
NR brings 50-plus years of practical experience in developing safe, rugged, reliable, compact and long-lived reactor systems designed to operate in unforgiving environments. NR is a joint DOE and Department of the Navy organization responsible for all aspects of naval nuclear propulsion.
The partnership is responsible for developing the first NASA spacecraft, the Jupiter Icy Moons Orbiter (JIMO), that will take advantage of a nuclear-reactor energy source for exploring our solar system. JIMO will visit Jupiter's three icy moons, Ganymede, Callisto and Europa. These icy worlds, in particular Europa, are believed to have liquid-water oceans, under a thick layer of ice on their surfaces, which could potentially harbor life.
The reactor system will provide substantially more electrical power. This will greatly enhance the capability of ion-drive propulsion, the number and variety of scientific instruments on the spacecraft, the rate of data transmission, and orbital maneuvering around Jupiter's moons.
'NASA sought this partnership because NR has an enduring commitment to safety and environmental stewardship that is a requirement for an undertaking of this magnitude,' said NASA Administrator Sean O'Keefe."
--Cindy
We all know [i]those[/i] Venusians: Doing their hair in shock waves, smoking electrical coronas, wearing Van Allen belts and resting their tiny elbows on a Geiger counter...
--John Sladek (The New Apocrypha)
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I'm glad to see the Navy getting on board here. They have the best safety record in the world with nuke reactors. I know a guy that was in the nuke program when he was in the Navy - the school has something like a 95% dropout rate. They're pretty unforgiving to candidates and toss anyone who shows the slightest sign of not being competent.
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