From: sylvia@email.invalid   
      
   On 15-Feb-21 7:16 am, JF Mezei wrote:   
   > On 2021-02-13 20:30, Sylvia Else wrote:   
   >   
   >> 400km, I get a difference in orbital speed of 20m/s or 90km/h at the   
   >> point where they meet.   
   >   
   > Thanks. So that would make in into the realms of "possible" as opposed   
   > to some speed difference in 1000kmh.   
   > If the shuttle has some fuel left, it could just burn all it's got to   
   > reduce that speed gap at last minute before falling back to perigee and   
   > eventually break up when it falls into atmosphere.   
      
   The closer it gets to matching the speed of the ISS, the closer it gets   
   to matching its orbit. Any burn that reduces the speed difference is   
   also circularising the shuttle's orbit, raising the perigee, so there's   
   no scenario in which the shuttle subsequently falls into the atmosphere,   
   at least not in the short to medium term (atmospheric drag still gets it   
   in the end, but it would take years).   
      
   >   
   >   
   >> A long enough bungee could cope with the 20m/s second difference,   
   >   
   > Could a Progress/Dragon stand by with lots of bungee cords attached to   
   > it, and reduse its speed by 90kmh just as shuttle passes by,  shuttle   
   > crew grab on to bungees and Progress/Dragon then re-accelerates back to   
   > ISS? (forgetting issue of thrusters firing towards crew, just cruiosu if   
   > the vehicles and fuel on there would be realisty, or whether such a   
   > manoeiver woudl take too much fuel.   
      
   Just for the record, I got deceived by Excel's formatting, and the   
   difference is 26.78 m/s or 96.42km/h.   
      
   I dare say one can conjure up workable situations involving bungee   
   cords, but once one's involving reentry capsules with sufficient fuel,   
   one would surely just use them to rescue the astronauts.   
      
   Sylvia.   
      
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