Descent of Iridium 9 (#24838)

From: Tony Beresford (
Date: Fri Oct 20 2000 - 21:22:18 PDT

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    The descent of Iridium 9 has changed in character.
    Somewhere between 22h UT Monday October 16, and 21h UT
    Tuesday October 17, the satellite controllers put all
    their effort into lowering the perigee, rather than 
    keeping the orbit circular as they had been doing. Since then
    the apogee has remained near 650Km height and the perigee height has been
    decreased to 587Km. This averages about 14 Km/s a day, a lower
    rate than the 18-19Km/day acheived previously. However it probably
    uses less fuel, as only one period of thrusting per orbit
    needs to be done. A side effect is a continuous increase in
    the eccentricity of the ellipse. This means the long axis
    of the satellite wont always be exactly on the local vertical,
    which may effect the atitude control algorithm being used,
    and the ability to predict flares as the orientation wont
    be known as precisely as before.
    Tony Beresford
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