D Tibbets wrote:In reply to djolds1 comments; I'm sure people with much more knowledge than me have crunched the numbers. My impressions are based on vague hand waving.
D Tibbets wrote:Any nuclear propulsion scheme converts nuclear potential energy into directed kinetic energy, and have to resist the thermal and radiation loads involved.
Thermal loads last for microseconds per pulse, and shielding when your craft masses 1000 tonnes+ is not much of an issue.
D Tibbets wrote:The penalty I see with the pulse detination approach is the additional weight needed to absorb the blast energy, and in this case providing recycled power for the next laser ignition cycle. Of course this would have to be compared to the weight dedicated to other hypothetical power sources (fission or fusion). Also, back in the 1950's and 60's the estimates of the laser input energy needed to achieve ignition was ,I'm guessing, several orders of magnitude less that what has been shown.
Winterberg has been obsessed for several years with using pulsed relativistic electron beams driven by Marx Banks to fire small
DT nuclear detonations. One scheme of his from a few years back had a Q of 1000 (not a typo) on the math. Per the usual fusion rule of thumb, multiply that by 10% for the actual hardware performance.
http://www.fusor.net/board/getfile.php? ... tt_id=2414
So order of magnitude requirements on beam initiated fusion may be doable.
D Tibbets wrote:This would mean several orders of magnitude more energy that has to be captured, processed and fed into more robust lasers for the next blast. I don't know how scaling would work out, but I'm guessing it would take alot more than a few hundred thousand pounds.
Winterberg also likes fusion-fission hybrids. IOW a Teller-Ulam setup without the fission primary. Small fusion unit fires fission in a U238 layer which causes LiD to fuse which... Stack until sufficient energy is achieved. Requires minimal additional mass. Consider the above document, but have the metallic liner be U238 or Th.
Winterberg is quite the Orioneer in spirit. Or the Dr. Strangelove if you're feeling less charitable.
D Tibbets wrote:Added weight means you need more thrust- explosive size and or frequency for the same net acceleration, which would put even larger engeenering loads on the structure and systems, especially for boosting into LEO,
All issues addressed by the original Orioneers (Taylor, Dyson, etc.), and not significant problems when you have 4000 to 10,000 to 100,000 metric tonnes
of structural mass to work with. The problem is getting your head around riding to orbit by setting atom bombs off under your a**.
D Tibbets wrote:more 'mostly' clean fusion bombs being detonated within the atmosphere.
Politics. The inevitable problem with the various nuclear propulsion designs.