From: twomack@chiark.greenend.org.uk   
      
   In article <420a2ed8$0$70247$ed2619ec@ptn-nntp-reader03.plus.net>,   
   Ian Stirling   wrote:   
   >tribolumen  wrote:   
   >> Does anyone know of a method, or a piece of software, for calculating (or at   
   >> least approximating) low-thrust interplanetary trajectories?  Most of what   
   >> I've found so far is PhD theses about using calculus of variations for fun   
   >> and profit.  While I can handle a little math (my undergrad degree is in   
   >> physics), I'd rather not deal with that level of it if I don't have to.   
      
   I've implemented a straight Runge-Kutta integrator (got the planetary masses   
   and   
   positions from BOTEC), and tried to plot courses, but it's not in the slightest   
   an easy problem.  I suspect I was looking at a hideously hard task (I wanted to   
   end up in Iapetus orbit; writing this just after the first Cassini pictures   
   appeared), but I couldn't even get sensibly to Jupiter.  All I discovered was   
   that   
   pointing the ion engine in the direction of Jupiter and assuming inexhaustible   
   fuel   
   doesn't work, you just bounce entertainingly around the solar system.   
      
   [I was assuming that a Jupiter encounter was still necessary for a low-thrust   
   trip   
   to the outer solar systems; my real question is how you stop at Saturn,   
   particularly   
   given how fast you're going after the Jupiter boost]   
      
   Tom   
      
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