From: tkoenig@netcologne.de   
      
   David Ellis  schrieb:   
      
   > I recently did a bit more in-depth reading on the ever-useful   
   > Atomic Rockets website to try and get a sense for what I would   
   > want out of a laser used for such applications.  My general idea   
   > is to use a phased-array, near-ultraviolet laser (I settled on a   
   > wavelength of around 250 nanometers, because why not) that would   
   > deliver energy in a series of microsecond pulses at a rate of four   
   > pulses every second.   
      
   > My hope is to justify a laser that could deliver energy at a   
   > rate sufficient to cause impulsive shock effects in steel at a   
   > range of 500 kilometers.  This is partly a goal, and partly a   
   > starting base-line for my own calculations.  As a base-line, I   
   > was also thinking of average power consumption comparable to the   
   > ~5 megawatt chemical oxygen-iodine laser used on the Air Force's   
   > YAL-1 prototype.   
      
      
   > I calculated the power required to vaporize steel   
      
   What is the enthalpy for vaporizing steel you used?   
      
   Looking around for a bit, I get ¨ 1500 kJ/kg for heating steel up to   
   1500°C, 272 kJ/kg for melting, 6340 kJ/kg for vaporization (ouch!) and   
   around 1100 kJ/kg for heating liquid iron to its boiling point (ok, so   
   that will be lower in vaccum).   
      
   So, to use a round figure, let's say 9000 kJ/kg.   
      
   > at a rate that would exceed the velocity of sound in steel, and tried   
   > to work back from there using Atomic Rockets's laser equations,   
   > treating the phased-array laser as a unitary laser system with a   
   > 2.5-meter lens.   
      
   > If I take the energy of a one-second beam at 5 megawatts and divide it   
   > into fourths,   
      
   So, 1250 kJ per pulse.  You can evaporate approximately 0.14 kg of iron   
   with a single pulse.  The iron molecules will travel at approximately   
   1000 m/s (Boltzmann velocity).  Half of them will hit the wall,   
   at an average effective velocity at ~ 500 m/s (there, I was to lazy   
   to work out the factor exactly), so an impulse of around 35 N*s.   
      
   So, you hit the armor with a sledgehammer of 5 kg hitting at 7 m/s   
   (which is not unreasonable if you would lift the hammer over your head).   
      
   Considering the impulse will be spread out over a large area,   
   the damage to any reasonable armor will probably be small.  Ear   
   protection will probably be required for people on the inside :-)   
      
   --- SoupGate-Win32 v1.05   
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