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

From: John Gardner (gardjw@juno.com)
Date: Thu Mar 23 2000 - 09:35:58 PST

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    Hi
    
    On Thu, 23 Mar 2000 07:12:49 -0800 (PST) Virgil <VFenn1@excite.com>
    writes:
    >
    >On Tue, 21 Mar 2000 10:13:30 EST, John Gardner wrote:
    
    >  Doesn't USSPACECOM already have the following capability?
    
    snip<
    
    First a commentary:
    
    USSPACECOM does indeed have the ability.  So how come MOTOROLA
    doesn't "contract" them to do the work in the interest of International
    public safety?  My personal opinion is they _will_ contact USSPACECOM
    in the end (no -----) for help.  Just imagine the possible corporate
    consequences of one or more goofs!
    
    snip<
    
    >  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 kilometers.
    
    Agree.  I've found several references to NASA documents on the subject
    but require one to order (pay) them...not viewable as web documents. :)
    
    NASA STI document numbers:
    
    Launch collision   19990079384
    
    Orbital collision  19810059184 A (81A43588)
                       19720022183 N (72N29833)
                       19950031158 A (95A62757)
    
    >  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?
    
    snip<
    
    | 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 true.
    
    I was just wondering as a study unrelated to satellites...but I agree.
    Do remember though the "big sky theory" for airplanes. Nobody is buying
    that one anymore.
    
    Workable analogy is a operational olympic size swimming pool to
    represent orbital space. A grain of fine desert sand for the total size
    of all man made objects. Crush the grain to dust and scatter it within
    the pool. For all intents and purposes, you, a spacecraft, will not
    'find' any part of it.  For now that is.  Provide enough sand dust....
     
    | 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?
    
    About what it would take to make WINDOWS an un-bloated and fully
    reliable operating system. :)  But seriously the IRIDIUMs don't have
    the fuel or time/money to do it on their own.  Then there's that pesky
    collision possiblity.
    
    John Gardner
    
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