From: mvp@web1.calweb.com   
      
   In article ,   
   0something0   wrote:   
   >The only problem with this is that the projectile is moving at   
   >nearly the speed of light, so when you see it, its already   
   >there, which means its going to take some handwavium to create   
   >an early-warning system, whcih would involve FTL communications.   
      
   Unless you're doing some sort of skiffy handwavitronics drive,   
   the propulsion just about has to be coming from something   
   external.  At .87c, the kinetic energy of the warhead is mc^2.   
   I.e., the energy it would have if you had total conversion to   
   turn it entirely into energy, or if it were pure antimatter.   
      
   (Yeah, if it were antimatter, double the mass for the normal   
   matter it anihilates with.  But then, around half the energy,   
   more or less, escapes as neutrinos, so it's a wash.)   
      
   Increase the velocity, and the kinetic energy of the warhead   
   is some multiples of its mass times c^2.   
      
   You can't carry that much energy.   
      
   So, the propulsion energy just about has to be applied   
   externally, from the launching site.  You might be able to see   
   the laser/particle beam/whatever used to push the warhead up to   
   near-c.  Accelerating it up to that velocity would take a while,   
   and some of the propulsion energy is likely going to leak past   
   the warhead, and run well ahead of the warhead, even if the   
   warhead is going .999c when it arrives. (Think Murcheson's Eye.)   
      
   (How fast would a 1-ton warhead need to be going for its   
   Bragg peak to put it at the core of the planet when it stops?)   
      
   --   
   "The urge to save humanity is almost            | Mike Van Pelt   
     always a false front for the urge to rule."   | mvp at calweb.com   
                     -- H.L. Mencken               | KE6BVH   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)