From: snidely.too@gmail.com   
      
   JF Mezei was thinking very hard :   
   > On 2022-01-10 02:44, Snidely wrote:   
   >   
   >> You can start with looking up a Hohmann transfer orbit.   
   >   
   > This was mentioned as the usual method to goto Mars. And you just said   
   > it wasn't going to Mars.   
      
   Correct.  Hohmann orbits can be used anywhere in the solar system (or   
   within other star systems.   You may be able to use them between star   
   systems, but I haven't check the math for that.   
      
   > And in going to Mars, you raise your orbit around the sun with your   
   > orbital speed matching your orbital altitude. Towarsds the end, Mars'   
   > gravity gives you any assist needed to match its speed/altitude above   
   > sun when it "invites" you to crash onto its surface.   
      
   yes, because otherwise, you keep transferring back to your starting   
   point.  That's how Mars Cyclers work.   
      
   > JWST wants to raise its altitude around the sun, but have the wrong   
   > speed for that altitude, unless you are at one specific altitude and   
   > point with the earth between you and the sun.   
      
   Part of station keeping will be doing the insertion burn.   
      
   > So still not obvious to me how it gets there.  Is it really one firing   
   > near Earth in the right direction with its new speed progressively   
   > decresing as it is slowed by ever weaker Earth's gravity with the hopes   
   > of its vertical speed reaching 0 at the L2 point?   
      
   Roughly speaking, yes.   
      
   > Does this mean that its trajectory to destination will always keep the   
   > earth between it and the sun? or is there some period where it might be   
   > ahead of the earth which will catch up?   
      
   I haven't plotted the transfer orbit.  But no doubt some simulators   
   around the web have.  Maybe you can even do it Kerbal.   
      
   I would expect that the angular speed would stay near that of Earth and   
   that of L2.   
      
   >> It's coasting up that hill.  Almost all that fuel is for station   
   >> keeping, with just a little for course correction on the way there.   
   >   
   > Did stage 2 do all the heaby work? if so, conceptually, wouldn't it also   
   > reach L2?  (I assume some burns created sufficient separation, but   
   > generally, won't it have the energy to go to same altitude?)   
      
   Yes.  It likely won't reach the actual L2 sweet spot, as it won't be   
   doing the course corrections, and it's likely to continue orbiting the   
   Earth in a highly ellipitical orbit.  It is possible, though, that ESA   
   did tweaks to it after separation to put it into a solar orbit.   
      
   /dps   
      
   --   
   "I am not given to exaggeration, and when I say a thing I mean it"   
      _Roughing It_, Mark Twain   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)