Iridium
9 Being Deorbited
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Unrelated to the
company's bankruptcy proceedings, Iridium 9 is being deliberately
de-orbited due to component failures. Several months ago Iridium 9
experienced an attitude control system component failure. It has
operated in a backup control mode since that failure. Recently a
second critical attitude control component began to exhibit signs of
impending failure. Such a failure would have left the vehicle only
partially controllable and incapable of supporting normal mission
operations. In mid-September the satellite was withdrawn from the
constellation and placed in an "engineering orbit" (30 km
circular below the nominal mission altitude). It was left in that
orbit while ground controllers monitored the situation. In late
September the failure of the second critical component did occur, so
a deorbit maneuver was immediately commanded in response. The
deorbit maneuver consists of regular thruster firings intended to
lower the orbit perigee to a target value of 250 km. The 250 km
altitude was selected as being low enough that atmospheric drag
should cause reentry within 1 year. Various considerations such as
increasing atmospheric drag coupled with the degraded attitude
control capability could result in loss of attitude control prior to
reaching that target altitude. Two spare satellites remain in plane
5 of the constellation.
The deorbiting of
Iridium 9 does not signal the initiation of deorbiting of the entire
constellation.
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