From: alain245@videotron.ca   
      
   On Jan/11/2022 at 12:59, JF Mezei wrote :   
   > On 2022-01-10 19:59, Snidely wrote:   
   >   
   >>> 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.   
   >   
   > Earth Sun is 147.12m km   or 105,000 kmh to do 1 lap in 365.25 days   
   > JWST  Sun is 148.7m km    or 106,000 kmh to do 1 lap in same time.   
   >   
   > So is this just a case of throwing a ball straight up so it's apex is at   
   > L2 altitude, and in doing so, also add 1000kmh horizontal speed so that   
   > at apex/L2, its horizontal speed maintains angular speed around sun the   
   > same as Earth's ?   
   >   
   > I was taught that raising orbit is done by accelerating horizontally   
   > which result in increase in altitude and decrease in horizontal speed.   
   > Just trying to square the two methods and what happens to horizontal   
   > speed when you are thrown up vertically.   
      
   If you have some horizontal speed and you accelerate vertically, you   
   don't add to your horizontal speed. You will lose some horizontal speed   
   as you approach apogee and then gain it again as you come down to perigee.   
      
   You really need to compute orbital trajectories to understand why. But   
   there is one important difference between accelerating horizontally and   
   vertically that might help you understand why accelerating horizontally   
   will give you a vertical push up but accelerating vertically doesn't   
   give you a horizontal push side way. While you are in orbit, the   
   directions of vertical and horizontal are constantly changing. If you   
   are in a circular orbit, your current direction of motion (horizontal)   
   is 90 degrees of your direction of motion in a quarter orbit. So if you   
   accelerate horizontally, you are accelerating in a direction that will   
   be vertical up in a quarter orbit. Therefore, it isn't surprising that   
   your excess speed over what is needed for circular orbit, will be used   
   for going up. On the other hand, if you are in a circular orbit, then in   
   one quarter orbit, you will be going in a direction that you are now   
   considering to be vertical down. So if you accelerate vertical up, you   
   are taking away from the speed you will have in a quarter orbit.   
      
   I hope this helps you. But as I said, you really need to compute orbital   
   trajectories to really understand what is going on here.   
      
      
   Alain Fournier   
      
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