From: sylvia@email.invalid   
      
   On 05-May-21 4:31 pm, JF Mezei wrote:   
   > Sanity check:   
   >   
   > If there were no atmosphere/drag, a satellite at 163km that is going at   
   > 28,080kmh and reduces it speed by 1kmh, would simply drop in altitude   
   > and now be at a lower orbit, correct?   
   >   
   > Theoretically, it could progressively reduce its speed and drop in   
   > altitude and end up going 28,440km in a orbit 100m above surface. Correct?   
   >   
   >   
   > Now, let bring is a purely theoretical chinese boosters called CZ-5B   
   > that is uncontrolled in a 163*301km orbit and bring back atmosphere.   
   >   
   > With every perigee having a bit of drag how is the orbit changed? Is   
   > only Apogee loweree? Both are changed equally? or does Apogee lose more   
   > altitide than perigee with tendency to circularize?   
   >   
   > If it circularizes, is it correct to state that the length of time spent   
   > at/near perigee altitude (and thus getung drag) increases?   
   >   
   > Since in an elliptical orbit, the object goes faster than required at   
   > perigee (hence having enough "oumph" to climb back up to apogee), I am   
   > curious at how the object eventually comes to a point where  drag lasts   
   > long enough to bleed enough speed to turn off orbital mechanics and turn   
   > on ballustic re-entry.   
   >   
   > Is there a magic altitude below which atmpsphere is instantly much more   
   > dense, so the minute perigee drops below that altitude, it bleeds too   
   > much speed to climb out of altitude that has drag and it is sayonara?   
   >   
   > Or is re-entry much more subtle and gradual?   
   >   
   One way of thinking about this to remember that the object is subject to   
   drag all around its orbit. The drag at apogee reduces the perigee, and   
   the drag at perigee reduces the apogee.   
      
   Just that for non-circular orbit, the drag at apogee is very small   
   compare with the drag at perigee, so the apogee is reducing while the   
   perigee stays pretty much unchanged.   
      
   Since the apogee is changing, it's not strictly speaking true to say   
   that the orbit is elliptical, and it's also not strictly speaking true   
   to say that it becomes circular. Rather, the orbit becomes a spiral,   
   with the orbital height continuously reducing. The rate of reduction   
   itself increases with time (though things like sun spots affect the   
   atmosphere on Earth, which can cause some variation). Eventually the   
   rate of reduction becomes so high that it is not possible for the object   
   to complete an orbit, and you have your ballistic reentry.   
      
   Sylvia.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)