Re: Off topic. IRIDIUM--2573 objects in harms way

From: Virgil (
Date: Thu Mar 23 2000 - 07:12:49 PST

  • Next message: Tony Beresford: "march 23 observations"

    On Tue, 21 Mar 2000 10:13:30 EST, John Gardner wrote:
    >  Hi All,
    >  Off topic.
    not so far of IMHO
    >  Doesn't USSPACECOM already have the following capability?
    >  Motorola made made mention of writing a program for the
    >  de-orbiting of IRIDIUM sats.  One cooperate purpose I assumed
    >  was minimizing _possible_ collisions (payments!) with objects
    >  whose perigee was less than IRIDIUM's nominal apogee of 779km.
    >  Note: 16 IRID's have apogees less than 779km plus 12 more that
    >  are higher.  For purposes of this post all 88 birds are 779km.
    >  The number of potential objects thus found 'in harms way' is 2573.
    >  For those who *enjoy* probability studies (I guess the first
    >  question has already been answered somewhere)...a request.
    >  1)  What is the statistical risk of collision with an orbiting
    >      object when a satellite is launched?  When decaying? Assume
    >      for both either LEO, MEO or HEO sought/lost.
    my guess is that is very low, but the launch planners treat it as
    significant because they want to miss any possible collision by lots of
    >  2)  What are the odds of a collision based on 88 random attempts
    >      to strike any of 2573 objects in a volume 3 times the Earth's;
    >      all traveling at 17K mph in a time frame of 2 weeks?
    >  For question 2, please disregard _all_ Earth orbiting satellite
    >  factors.  An answer relevant to satellites would require factors
    >  bordering on the theory of CHAOS. :)
    I haven't seen any answers, yet, and I don't know either. But i would
    suppose that the problem would reduce to a comparison of the volume of space
    traced out by the various satellites relative to the volume of space
    available.  I also suspect that the result would not be very meaningful
    because the underlying assumption that the orbits are random, is far from
    In any case, I sure wish we could save all that expensive Iridium mass
    already in orbit for later. Surely it would be useful for radiation
    shielding or something someday. What would it take to park stuff like that
    at L5?
    ..Virgil..         email 
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