From: andrewbetter@gmail.com   
      
   Hello again,   
   So I was running some more spreadsheets on the feasibility of various space   
   weapons (standard lasers, bomb-pumped lasers, Casaba Howitzers), working from   
   some real world nuclear warhead and reactor numbers and the efficiency   
   estimates and equations from    
   Atomic Rockets.   
      
   I seem to have run across a useful idea, although I'm not sure, so I wanted to   
   ask about it here.  I found that a Casaba-Howitzer, though massively powerful,   
   seemed to be significantly less effective than a nuke-pumped laser with the   
   same kiloton charge.    
    I also realized that most of the issue with the bomb-pumped laser is that the   
   energy is divided among 50 or so rods pointed in all directions.  So I   
   figured, what if a Casaba-Howitzer pumps the laser instead?  Assuming my   
   calculations are correct, the    
   Casaba-Howitzer cone is about 0.25% square degrees of a sphere, which means   
   that if an omnidirectional nuke-pumped laser has 50 rods, a Casa   
   a-Howitzer-pumped laser would focus the energy into a single rod (actually   
   one-eighth).  Even assuming 50% shaped    
   charge efficiency, this results in a laser that applies about 30 times more   
   energy for a given kiloton yield than a traditional nuke-pumped laser.   
      
   This basically results in a ridiculously powerful missile warhead.  For   
   example, if we use a 75000-kiloton warhead (large, but bear with me), assuming   
   80% laser rod efficiency and a beam divergence of 20 microradians, this   
   results in a beam that applies    
   about 25kJ/cm^2 over a circle 4000m in diameter at a range of 200,000km.  This   
   means that if the target ship has a max acceleration of 10Gs (about max human   
   tolerance), and it takes 0.67sec for missile's sensors to receive data from   
   the enemy warship due    
   to lightspeed, 0.5sec for the missile to aim and fire, and 0.67sec for the   
   laser to arrive--the enemy ship could only displace 200m from its predicted   
   position 2secs ago when the missile's input dates from.  And since the laser   
   circle is 4000m in    
   diameter, there is no way the enemy ship could evade.  Plus, at this kind of   
   range, it'd be quite difficult for the ship to destroy the missile with its   
   own lasers.   
      
   In other words, given a fairly large kiloton yield, there could be no defense   
   against missiles fitted with this type of warhead, besides interceptor   
   missiles.   
      
   So I was kind of wondering--   
   Does this make sense?  Is this a legitimate possibility?  Are my calculations   
   correct?  I kind of figure someone would have thought of this already, so I   
   was curious since I hadn't really seen anything that would suggest this   
   possibility.   
      
   Thanks.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)