From: sylvia@email.invalid   
      
   On 24-May-21 6:44 am, JF Mezei wrote:   
   > On 2021-05-23 06:05, Sylvia Else wrote:   
   >   
   >> No, there is no way this can evolve into anything other than a rich   
   >> man's toy. It's a dead end.   
   >   
   >   
   > Tried to use some ballistic trajectory calculator, but it assumes a flat   
   > Earth :-(  (aka: human throwing a ball in a park).   
   >   
   > In orbit, I can understand the concept that as the satellite moves   
   > forward, the curvature of Earth below results in the ground dropping   
   > lower, and if you free fall down at the same rate as the ground drops,   
   > then your altitude over ever changing ground remnains stable and you are   
   > in orbit. is that correct understanding?   
   >   
   > If I manage to travel 1/4 the way around the Earth, will the ground have   
   > dropped by 6371m (Earth radius) ?   
   >   
   >   
   >   
   > In the case of a suborbital London-Sydney flight, is this a case of   
   > finding the right combo of altitude and speed at apogee/MECO such that   
   > your fall rate is slow enough that you will travel most of the distance   
   > before your altiutude drops to re-entry interface at which point you   
   > become a glider and travel a few hundred km?   
   >   
      
   The major problem is that you have to climb above essentially all the   
   atmosphere, or the the vehicle will melt from the heating caused by   
   moving through the atmosphere at such speeds. If you managed to avoid   
   the melting you'd still need continuing thrust (so need fuel, and lots   
   of it) to avoid slowing down. This is not practical.   
      
   So you have to achieve near orbital speed, or you'll come down short of   
   your target.   
      
   Now when re-entering, you have to get rid of all that kinetic energy,   
   without melting.   
      
   Virgin Galactic is completely ill-adapted to doing any of these things.   
      
   Sylvia.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)