XPost: sci.military.moderated   
   From: pfaustin@bellsouth.net   
      
   "John Schilling"  wrote in message   
   news:c7usrb$p5g$1@spock.usc.edu...   
   > "Paul F Austin"  writes:   
   >   
   > >As I said in another answer, a 1MT exo detonation detonated just above   
   the   
   > >atmosphere would deposit about 3MRad at GEO. That's gamma. The sun's   
   > >emissions are dominated by electrons with a minority of protons.   
   Electrons   
   > >are relatively easy to shield against (high energy protons are not). As a   
   > >result, flares and all, a GEO sat is designed to withstand about   
   35-50KRAD   
   > >over life. A design margin of 2 or 3 is added getting you close to   
   > >100-150KR.   
   >   
   >   
   > OK, math time.  Your 100-150 kRad figure corresponds with my own   
   experience   
   > designing flight hardware.  But, one megaton in LEO giving 3 MRad in GEO?   
   > Not buying it.   
   >   
   > One megaton is 4.2E15 Joules.  LEO to GEO is about 3.5E7 meters, depending   
   > on how we define "LEO".  One Rad is 0.01 Joules per kilogram of deposited   
   > energy.  And typical shielding density for unhardened spacecraft   
   electronics   
   > is still on the order of 100 mils of aluminum, mass density of 6.85   
   kilograms   
   > per square meter.   
   >   
   > One megaton in LEO produces an integrated flux of 4.2E15/(4*pi*3.5E7^2)   
   > or 0.27 J/m^2 at GEO.   
   >   
   > If every erg released by the detonation is gamma radiation, with a   
   spectrum   
   > optimized for energy deposition just inside 100 mils of shielding, that   
   gives   
   > us 0.27 / (e * 6.85) = 0.0125 joules per kilogram at the target   
   electronics.   
   >   
   > A little over *one* Rad, not three million.   
   >   
   >   
   > I do not see how prompt gamma or X-ray radiation from a nuclear detonation   
   > can be anything more than a very local hazard to satellites.  The 100-kRad   
   > level will be reached only at distances of a hundred kilometers or so.   
   >   
   > A high-altitude nuclear detonation can be a global hazard to satellites in   
   > *Low* Earth Oribit, but that's from the high-energy electrons, in part due   
   > to magnetospheric trapping (a short-lived but intense Van Allen belt) and   
   > in part due to atmospheric interaction producing an electromagnetic pulse.   
   > The former isn't even limited to line-of-sight; one well-placed large nuke   
   > can take out every unhardened *LEO* bird.   
   >   
   > But the very same magnetospheric trapping protect the GEO birds from that   
   > effect.  And the numbers just don't add up for prompt X-ray/gamma.   
      
   John, the Moderator apparently killed my other post. Here's the source:   
      
   George Messenger's "The Effects of Radiation on Electronic Systems", 1986.   
   figure 4.23. Now for the mea culpa. I misread the figure and you are   
   correct. The prompt dose for a 1MT exo detonation at 200Km is 10 Rad(Si),   
   not 10^11. Never Mind.   
      
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