Re: 25600 (more)?

From: Jim Scotti (
Date: Wed Oct 12 2005 - 16:45:26 EDT

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    Hi Pat,
        A satellite will spiral in if it is in a more or less circular orbit, but 
    an eccentric orbit like this ones, with small perigee and large apogee means 
    that it encounters atmospheric drag which slows its speed down when it is 
    near perigee only.  Slowing an object at perigee lowers its apogee halfway 
    around its orbit, so most of the decay is only in the apogee (but caused when 
    at perigee...) until the orbit is nearly circular when it decays much more 
    rapidly.  If the perigee drops due to luni-solar perturbations or other 
    affects, then if the perigee drops too low, it can re-enter at that point as 
    well.  If I remember right, the height at which it is unlikely to survive 
    another orbit is something like 60 kilometers.  I'm sure someone can be more 
    exact and it would depend on the drag coefficient and on the orbit 
    On Wed, 12 Oct 2005, wrote:
    > Last July 25600's apogee was 14,000 km
    > its perigee was 125 km
    > Now its apogee is 3056 km
    > its perigee is 111 km.
    > 11000 km off the top but a mere 15 off the bottom.
    > Why don't satellites spiral in?
    > Pat McNally
    > Seattle
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    Jim Scotti
    Lunar & Planetary Laboratory
    University of Arizona
    Tucson, AZ 85721 USA       
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