Re: Iridium removal

From: Alan Pickup (alan@wingar.demon.co.uk)
Date: Mon Mar 20 2000 - 13:47:00 PST

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    I agree with Tony Beresford that the thrust available to the Iridiums
    may be too little to force a controlled re-entry. And, like Tony, I
    suspect that the best they can hope for is to lower the perigee to
    somewhere below 300 km where they might only last a few weeks or months.
    At their present heights, I would guess that their lifetimes might be
    20-50 years.
    
    However, I think there is little possibility of arranging for a decay at
    far southern latitudes. One advantage of a Molniya's orbit is that its
    inclination is chosen so that the perigee point does not precess around
    the orbit. By placing the perigee near its southern apex, the most
    southerly point, the Molniya is "visible" for lengthy periods as it
    crawls through apogee over high northern latitudes (eg above Russia).
    
    The Iridiums, on the other hand, have inclinations near 86.4 deg so
    their perigees rotate "backwards" around their orbits at more than 3
    degrees per day. In other words, it would take less than a month for the
    perigee to rotate from near the N or S pole to the equator. Even if the
    decay can be controlled to within a few days, which I doubt, there is
    still no guarantee that it will drop in the vicinity of perigee.
    
    
    Alan
    -- 
     Alan Pickup | COSPAR 2707:  55d53m48.7s N  3d11m51.2s W   156m asl
     Edinburgh   | Tel: +44 (0)131 477 9144     Fax: +44 (0)870 0520750
     Scotland    | SatEvo page:   http://www.wingar.demon.co.uk/satevo/
    
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