Hi All, I just got this interesting information concerning the de-orbiting of Iridium 9 from a reliable source who wishes to remain anonymous. Regards, Chris -- forwarded text starts here --- Yes, IR9 is being deliberately de-orbited, but the reasons are completely independent of the business situation. That particular satellite experienced a significant attitude control system component failure a few months ago. It was operated in a backup control mode since that time, but more recently a second critical attitude control component showed unmistakable signs of impending failure. The second failure would leave the vehicle only semi-controllable and completely incapable of supporting normal mission operations. For that reason, the vehicle was taken out of the constellation and placed in a so-called "engineering orbit" (30 km circular below the nominal mission altitude) in mid-September. It was left in that orbit while ground controllers kept a watchful eye on the situation. Quite recently (just a few days ago), the anticipated failure of the second critical component finally did occur, so the pre-planned de-orbit maneuver was immediately commanded in response. The de-orbit maneuver consists of regular propulsive thruster firings targeted to lower the orbit perigee to a target value of 250 km. The 250 km altitude was selected many years ago 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, but they'll keep at it as long as possible. The important point is that there are still 2 spare satellites in that orbital plane of the constellation (Plane 5) and that the current situation with IR9 does not represent the commencement of a general constellation-wide de-orbit sequence. Motorola and Iridium are still working feverishly to close a deal with a highly-motivated prospective new owner, and all parties are both hopeful and confident that such a deal will be struck so that the constellation can resume full service. ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Mon Oct 16 2000 - 04:37:49 PDT