From: jrfrank@ibm-pc.borg.retro.com   
      
   "James M. Devine"  wrote in   
   news:2E3rc.22$F5.2099@news.uchicago.edu:   
      
   > Ian Stirling wrote:   
   >> The "stop itself in mid-orbit" is orders of magnitude harder than   
   >> the "drop straight down" bit.   
   >> You need the same amount of propellant to slow down as you do to speed   
   >> up.   
   >> You have burnt all the propellant you used to speed up, so you'r kind   
   >> of stuck.   
   > Actually, The vast majority of the energy spent is to get into orbit   
   > (increase altitude). Only a small relative proportion of it goes into   
   > lateral motion.   
      
   Incorrect. Most of the energy goes into kinetic energy (velocity), not   
   potential energy (altitude). For a 200 km orbit, for example, 94% of the   
   energy change is kinetic.   
      
      
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