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#11
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Michael Smith wrote:
Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. Why should this follow? RTGs are much more radioactive at launch than are reactors. The bigger problem with space reactors is development cost and lack of application. Paul |
#13
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Michael Smith writes:
On Mon, 14 Feb 2005 05:18:28 GMT (Henry Spencer) wrote: You can start with NERVA derivatives, and pursue more ambitious designs in parallel with the first expeditions. The one big hassle is low-emissions test facilities, and it's one that should yield quickly to substantial amounts of money -- no breakthroughs are required. Liquid-core or nuclear-lightbulb is substantially better, and gas-core is much better, although they are longer-term options with significant development issues. Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. A nuclear-electric thruster system, while inefficent, can at least be built from well understood components. I'm not following your logic. The "political problems associated with simple RTGs", were entirely due to A: some minor but non-negligible safety issues pertaining *only* to RTGs and not to any other space nuclear power system, and B: the fact that they used the N word. "Nuclear rocket" and "nuclear electric thruster system", both use the N word. If the political problems associated with simple RTGs will suffice to kill the one, they will just as surely suffice to kill the other. In fact, the political problems associated with simple RTGs, were overcome, and the RTGs flew. With that trail now blazed, I don't think nuclear systems are unthinkable. But if they are, they are *all* unthinkable. -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-718-0955 or 661-275-6795 * -58th Rule of Acquisition * |
#14
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Speaking of such matters, see http://www.spaceref.com/news/viewsr.html?pid=15443 In particular see the Power Point (sorry) presentation "Session 6: Human Mars Exploration Mission Architectures and Technologies" |
#15
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Paul F. Dietz wrote:
Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. Why should this follow? RTGs are much more radioactive at launch than are reactors. Indeed, a point that's often overlooked. RTGs start at peak radioactivity and then decay. A reactor can be launched inert, with sod-all radioactivity, and then sent critical when in a safe orbit (I recall c. 1000 miles being a figure mentioned in a debate on this here quite a while ago). The bigger problem with space reactors is development cost and lack of application. Yes. For electicity generation, compared to RTGs a reactor is much more complicated, much more expensive to develop and probably much heavier and bulkier. There just hasn't been anything that's needed the sort of high long-term power a reactor can put out. A manned mission to Mars, though... Nuclear rockets (I include the type of HET array being suggested in this definition) are another matter. So far there hasn't been anything that hasn't been able to be done with chemical rockets. However (again) a manned mission to Mars could well be such a mission; the problems of bone loss and radiation exposure could prove to be such that a nuclear rocket would be the only way to get there in a time that would keep the crew in condition to actually do something when they got there, let alone back on Earth. You'd have the weight of shielding to consider, and it could be a trade-off between radiation from the engine and radiation from space. (ie light shielding may allow sufficiently faster acceleration and hence shorter journey times that you actually reduce overall radiation exposure). I'm a great fan of Stephen Baxter, but his novel "Voyage" really doesn't do the NERVA nuclear-thermal rocket program justice; it was both saner and more successful than he makes out. For a start, in theory at least with the hydrogen fuel radioactive emissions were limited to the 2% or so of hydrogen that was deuterium. Of course the problem was that bits of engine got spat out the back as well, but it was acceptable by '60's standards. Of course you'd have to be more careful now. -- Malcolm Street Canberra, Australia The nation's capital |
#16
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Malcolm Street wrote:
Paul F. Dietz wrote: Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. Why should this follow? RTGs are much more radioactive at launch than are reactors. Indeed, a point that's often overlooked. RTGs start at peak radioactivity and then decay. Almost true. But, the decay chain may make more radioactivity come out of the device as time goes on, and the output switches to hard to shield stuff. |
#17
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Henry Spencer wrote: The simplest way to address the food loop is not to try, given that freeze-dried food weighs less than half a ton per man-year. Generally, much the simplest and most reliable way to tackle a lot of the smaller recycling/ repair issues is brute force: more mass, and more fuel to push it, is cheaper than major engineering R&D. Of course, trying to sell that approach to R&D-oriented organizations is a bit of a challenge. "Anything which they do not wish to do is always lacking in technology. Whether single stage to orbit or Mars missions, the technology is never quite ready..." (Jim French) I don't know enough about long-term nutrition and related matters to have an opinion, but note that the manned-Mars presentation at the recent Mars roadmap meeting contains the following assertions at slide 21: http://www.hq.nasa.gov/office/apio/p...an_studies.ppt Closing the life-support air and water loops with low expendables is a key leveraging technology for long duration human exploration missions Current food preservation technology is not capable of providing nutritionally viable food for the longer mission durations under study. Food production technologies under the environmental conditions of these missions is not developed to the point of being the primary source of food. Power requirements for both closed loop life support and food production can be significant, indicating that advanced life support and advanced power systems are closely coupled. [Boxed summary] Closing the air and water loops is essential to reduce the total mass of long duration missions to a reasonable level. Improvements in food storage technology or production technology are also needed to reduce overall mass and ensure crew health. |
#18
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John Schilling wrote:
In fact, the political problems associated with simple RTGs, were overcome, and the RTGs flew. With that trail now blazed, I don't think nuclear systems are unthinkable. But if they are, they are *all* unthinkable. RTG-s being thinkable in some scenarios does not in and of itself make other nuclear systems so. These will have to do their own trailblazing, the more complex and the closer to Earth they have to operate, the more so. -- Sander +++ Out of cheese error +++ |
#19
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Current food preservation technology is not capable of
providing nutritionally viable food for the longer mission durations under study. I wonder...didn't some of the early Artic and Antarctic expeditions go several years without resupply? Jan |
#20
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Jan Vorbrüggen wrote:
I wonder...didn't some of the early Artic and Antarctic expeditions go several years without resupply? Does shooting seals count as resupply? Paul |
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