On Monday, 12 March 2018 03:27:42 UTC+8, Thomas Koenig  wrote:   
   > dsdy120@gmail.com  schrieb:   
   >    
   > > Several assumptions for the following calculations:   
   >    
   > > 1. Planet is airless and nonrotating   
   >    
   > OK.   
   >    
   > > 2. Attacker occupies circular orbits only.   
   >    
   > Hmmm...   
   >    
   > > 3. Defender fires projectiles straight upward - this makes sense   
   > > because defenders only care about altitude - not velocity. Anything   
   > > above 1 km/s generally starts becoming a bad day for either   
   > > combatant   
   >    
   > No, this does not make sense.   
   >    
   > Asuume you're in LEO, at 7.9 km/s.  You have 3.3 km/s delta v at   
   > your disposal.   
   >    
   > Now, you can add that delta v tangential to your velocity, giving you   
   > escape velocity, so you can hit everything in orbit around Earth.   
   >    
   > Alternatively, you can add the delta v perpendicular to your   
   > current velocity.  According to Phythagoras, this will give   
   > you a combined velocity of 8.56 km/s, so you get only 0.66 km/s   
   > additional velocity.   
      
   I'm assuming that defenders are firing from the ground, starting at zero   
   velocity If that is the case, any attempt to launch sideways results in a    
   lower apoapsis than can be achieved with a straight-up trajectory. I know   
   launching sideways is ideal for    
   orbit, but we need to look at our priorities - launching horizontally is   
   delta-v efficient, but certainly doesn't do a good job of maximising apoapsis,   
   which is all you really care about for an interceptor missile. If you have a   
   launch vehicle with 11km/   
   s of delta-v, you could spend 10km/s getting into low earth orbit and then an   
   extra 1km/s to raise your orbit several thousand kilometres, or you could   
   point the thing straight up, and get way more altitude.   
      
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