From: root@mauve.demon.co.uk   
      
   Earl Colby Pottinger  wrote:   
   > Anthony Frost  :   
   >   
   >> In message <1081649570.804846@haldjas.folklore.ee>   
   >>           Sander Vesik  wrote:   
   >>   
   >>  > Keith F. Lynch  wrote:   
   >>   
   >>  > > By the time it's noticed that a ship is approaching earth at 90% the   
   >>  > > speed of light, it's far too late to do anything about it.  And when   
   >>  > > it hits, it will devastate a continent.   
   >>  >   
   >>  > You need an early warning system that will spot any such 1-2 light   
   >> minutes   
   >>  > out and then you shoot a stream of protons at 99.9999+% of lightspeed at   
      
   >>  > it and watch it blow up.   
   >>   
   >> And hope it takes less than 12 seconds to get the cannon aimed and   
   >> firing. Much, much less than 12 seconds in fact because, even if you've   
   >> managed to destroy it, you've still got a cloud of lumpy plasma heading   
   >> for you at nearly 90% of lightspeed which isn't going to do your   
   >> atmosphere any good.   
   >   
   > You seemed to make very limited range for detection.  If the SS is detected   
   > one light year out then you have just over a months warning.  If you fire   
   > soon after that warning you show intercept the SS about 15-18 light days out.   
      
   That's a moderately dense net.   
   A light year out, a months warning.   
      
   Assuming a tenth of that is light travel time to the sensor, and assuming   
   it's passive, that's around a thousand detectors.   
      
   Then there is the interesting issue of how you detect a non-emitting   
   body being as stealthy as it can going past a light week away.   
      
   How brightly would such a body make interstellar plasma glow?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)