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Thread: NASA to go nuclear

  1. #241
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    Quote Originally Posted by publiusr View Post
    And may not take to well to shaking atop an LV. While going nuclear--why not go all the way and have asbestos fibers or rock wool for some uses http://en.wikipedia.org/wiki/Mineral_wool

    And as the case with STS, designs will be as much "This Old House" as aerospace...whatever works

    Also of use perhaps--water glass http://en.wikipedia.org/wiki/Water_glass
    1600K is probably too hot for asbestos

    Engineering is always "whatever works" and gives the most cost-effective results.
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  2. #242
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    True, but it will still have uses as insulation surrounding whatever reactor can hold up. I wonder if a working fluid can be passed through asbestos pipes...Some of the work-arounds for NSWRs and put-put Orion pusher plate cooling--advances in heat-shields and what have you might help with reactor designs...it might be something obtuse. Maybe from a field of research unrelated to nuclear power or even aerospace.

  3. #243
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    Quote Originally Posted by swampyankee View Post
    I used 300 K as an example temperature; I also said that their temperature would be set by system design issues; the choice of working fluid didn't come into the discussion. Most of the NASA studies have used alkali (period I) metals as the working fluid for Rankine systems. The Brayton cycle studies have used mixes of noble gases (usually Xe/He. The reason why has to do with practical limits for turbomachinery tip speeds and allowable diffusion coefficient vs tip Mach number). My expectation is that dynamic space-based nuclear reactors will tend to use alkali metal working fluids and Rankine cycles; the need to minimize fissile inventory and pressure vessel masses will tend to make gas-cooled reactors using Brayton cycles less competitive.

    So how about a lead cooled design? A big advantage to that is the coolant itself can double as shielding while still being able to run fairly hot. In fact, these were used in the Alfa class for a couple of decades before the class was retired during the breakup of the USSR. It seems to be fairly well known.

    It did seem that several of the posters were missing the rather significant design issue of the rejection of waste heat. Radiators are going to be a significant mass for a space-based reactor power system, regardless of the temperature chosen for rejection of waste heat.
    Based on my admittedly limited understand, the heat pipe concept seems promising as a solution to the problem. Also I would imagine that the construction material of choice would have some effect on radiator mass.


    At 1600K, most materials won't work. Refractories -- either ceramics or metals -- will be needed. While people use them all the time, they are not easy to process.
    But not impossible? Given that higher tempurature leads to lower radiator size and mass, I would think that the performance advantages would make it a worthwhile endevour.

    In anycase, according to table 1 in this it would be possible to achieve a radiator temp of ~800K using titanium with potassium as the heat pipe working fluid. In the context of future settlements on the moon (yes, they will happen in the coming few decades one way or another), this would make sense because the relative wealth of titanium in the Lunar Lowlands would reduce the amount of material needing to be imported from elsewhere. While it wont have the performance of that 1600k I mentioned, it should still be more than mass competitive with solar at comparable wattages. The ISS solar trusses by themselves have a mass of 79 metric tons, surely the system mentioned above can beat that.

    Engineering is always "whatever works" and gives the most cost-effective results.
    But the space shuttle was neither. :P

  4. #244
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    Quote Originally Posted by aquitaine View Post
    But the space shuttle was neither. :P
    Actually, the Shuttle did work, and gave the most cost-effective results possible within the requirements under which it was designed and the technology available at the time. One could, of course, argue that the reqs were bad (probably the most ruinous was DoD's cross-range requirement) and some of the design decisions were wrong.

    If the Shuttle had been able to meet its requirements, it would have been a much more cost-effective system. There's a system engineering course on the MIT OCW site which studies the Shuttle and its design process, using many of the original engineers as information sources; it's a great way to spend a about 2 dozen hours.
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  5. #245
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    Quote Originally Posted by aquitaine View Post
    S
    In anycase, according to table 1 in this it would be possible to achieve a radiator temp of ~800K using titanium with potassium as the heat pipe working fluid.
    That link is a nice find. I'ma give this one a good read trough once I'm able to get back to pondering anything else but earthly matters like going camping with a pack of cub-scouts. (it kinda resembles herding cats, but is more fun)

  6. #246
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    I'm surprised they didn't evaluate "NaK" in that heat pipe paper. This is a eutectic mixture and is liquid to below the water freezing point.


    http://en.wikipedia.org/wiki/NaK

  7. #247
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    I wonder if this may play a part: http://en.wikipedia.org/wiki/Borazon
    "Borazon is used in industrial applications to shape tools, as it can withstand temperatures greater than 2000 C (3632 F), much higher than that of a pure diamond at 871 C (1600 F)."

    In other news...SLS to use F-1 strap-ons:
    http://up-ship.com/blog/?p=14449
    http://spaceflightnow.com/news/n1204/18dynetics/
    http://forum.nasaspaceflight.com/ind...?topic=28693.0

    Perhaps nuclear upper stages can have a smoother ride...
    Last edited by publiusr; 2012-Apr-20 at 09:47 PM.

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