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Thread: Nuclear reactor propulsion systems and the militarization of space. Is it the next space race?!

  1. #1 Nuclear reactor propulsion systems and the militarization of space. Is it the next space race?! 
    Forum Ph.D. Double Helix's Avatar
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    Dec 2020
    The U.S. military, with their understandably insatiable appetite for advanced weapons, is exploring the use of thermal nuclear rocket systems for some of their future space-based assets (1). Basically what we are talking about is a "flying nuclear reactor", both on lift-off (as payload) and in space (end-use). That is scary enough, but they are also designed to function at maximum sustainable design temperatures (always a waving red flag), where the super-heated liquid propellants offer the highest thrust.

    Quoting from the Wiki reference (1):

    "As with all thermal rocket designs, the specific impulse produced is proportional to the square root of the temperature to which the working fluid (reaction mass) is heated. To extract maximum efficiency, the temperature must be as high as possible. For a given design, the temperature that can be attained is typically determined by the materials chosen for reactor structures, the nuclear fuel, and the fuel cladding. Erosion is also a concern, especially the loss of fuel and associated releases of radioactivity."

    end quote

    So what we have in this flying nuclear reactor is a critical mass of some fissionable isotope, presumably at relatively high purity to minimize "spacecraft" weight and maximize thermal yield (with lowest critical mass). This is then used to super-heat some propellant, most likely hydrogen, and exhaust it at very high temperatures without the need for ignition. Optimal designs are strictly limited by the temperatures the "thrust chamber" and its associated components can withstand.

    We are talking about military requirements here (i.e. maximum performance), so this likely means that the associated nuclear reactor would be able to create temperatures that no technology known to science could contain from catastrophic thermal failure, since the heat source must be higher than the propellant it is heating. Recall that we are after maximum thrust. Of course failures are potentially inherent in all advanced weapon systems, but these happen to be carrying a lot of radioactive materials, which quickly becomes waste if something goes sour. One can only wonder about the ramifications of such a race to militarize space with such complex and potentially super-hazardous systems. Launching many such reactors presents a threat itself, as might re-entry of errant ones, whoever owns them.

    In any event, DOD's Defense Advanced Research Projects Agency (2) just shelled out almost $30 million to three companies to research such systems and find a way to make them operational (3). The need for such unique propulsion systems in space is claimed to be due to the constraints of current technology, which is really limited to fairly slow speed systems. Chemical based rocket engines are not good enough for the agile systems the Pentagon has in mind (whatever they might be). So flying nuclear reactors might be the newest wave in space propulsion. It is unfortunate that it comes with such a nasty primary component.

    Some of us will be hoping that the global demand won't result in very many, if any, of these systems in orbit. One must recall the excesses during the Cold War - the world had tens of thousands of nuclear weapons. Hopefully we will not return to such insane over-kill in space.

    The use of such rocket engines to power spacecraft of discovery is another issue entirely. Most of these would be going out and not coming back. It could reduce the travel time to Mars by half, so NASA is also interested (2). Perhaps the pending R & D can yield a more practical advantage to both exploiting, and exploring space.




    Last edited by Double Helix; April 21st, 2021 at 06:41 PM.
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