From: schillin@spock.usc.edu   
      
   "tribolumen"  writes:   
      
   >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.   
      
   Sorry, but you have to.  Or, alternately, brute-force it numerically, but   
   either way there's nothing available to make your job easier.  Low-thrust   
   trajectories are ignored by most orbital mechanics people, and what work   
   is doen in the area is mostly two-body or perturbed two-body stuff for,   
   e.g., comsat orbit topping missions.  Interplanetary low-thrust work,   
   there aren't enough people doing it for it to be worth anyone's time to   
   polish up the tools for general distribution.   
      
      
   >Specifically, I'm trying to rough out a piloted mission to Mars using   
   >magnetoplasmadynamic thrusters.  I need to get an idea of flight times,   
   >launch window durations, and surface stay times for a given payload fraction   
   >and specific impulse.  I've found a number of pre-calculated mission plans,   
   >but I'd like to be able to modify them.   
      
   *Small* modifications can be treated as first-order perturbations, with a   
   little common sense and assuming you're looking for first-order answers.   
      
   Also, if your thrust is only "low" w/re planetary gravity, but safely in   
   the medium-to-high range w/re solar gravity, you can use (again, first   
   order only) a kludged patched-spiral-conic trajectory, in which escape   
   and capture are done as classic low-thrust spirals to Vescape and the   
   interplanetary trajectory is standard elliptic or hyperbolic transfer   
   orbit with a first-order adjustment for short but finite burn time.   
      
   This requires that you be quite comfortable with your two-body orbital   
   mechanics, both high and low thrust.   
      
      
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