From: sylvia@email.invalid   
      
   On 11-Dec-22 8:33 am, JF Mezei wrote:   
   > I may have asked this, but I guess never got proper answer.   
   >   
   > What is the exact actual meaning when media mention a spacecraft may   
   > skip on the atmosphere and be thrown out in space if it isn't precisely   
   > aimed for re-entry?   
   >   
   > Is this just a case of aircraft failing to aim towards atmpsphere dense   
   > enough to slow it down for re-entry and instead entering very elliptical   
   > orbit?   
   >   
   > Or are there actual aerodynamics involved where spacecraft would   
   > generate lift in thin atmosphere and gain altitude (and then get ito   
   > elliptical orbit?)   
   >   
   > And if the capsule has its het shield oriented to be perfectly   
   > perpendicular to direction of travel, would it still generate lift when   
   > it hits atmosphere?   
   >   
      
   It's not going to bounce off as if the atmosphere were some kind of   
   trampoline, because there's nowhere to store the energy temporarily in   
   the atmosphere (unlike a trampoline, which has springs).   
      
   But if a spacecraft is returning from the Moon, for example, it's going   
   very fast. If it hits the atmosphere at too shallow an angle, it may not   
   slow enough to follow the curve of the Earth. Its direction would   
   change, but as the Earth curves away, the spacecraft could find itself   
   back above the atmosphere, and now moving away. Not as fast as it was   
   originally going, but still fast enough to head off into space, not to   
   return for some time.   
      
   Plunging straight into the atmosphere at right angles would obviate   
   that, but now the problem is that the g forces build up very quickly,   
   and even if the spacecraft can be designed to withstand that, the humans   
   inside cannot. There's also the heating that arises when getting into   
   the denser atmosphere while still going too fast. Even heat shields have   
   their limits.   
      
   Sylvia.   
      
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