Iridium satellite number confusion continues

Thu, 6 Aug 1998 14:37:23 -0500

Observers of Iridium satellites should be very careful to note that I and
others have been confusing the common names of the satellites that we are
observing. This confusion is derived from the OIG data that comes from
USSpace Command. I reported yesterday that Iridium 46 was tumbling and in
fact, it is really Iridium 24. This has been known for some time and is not
a new failure. However, the reason for this is the coding that is produced
when we get our element sets from OIG.  When I print out my predictioins,
the common name that comes from OIG is printed out and I use it just as
everyone else does. 

Apparently, there are a total of 7 Iridium satellites that are not operating
normally from what we have observed and from the technical information that
has been provided to us on the net. There are two types of observations that
tend to confirm that a satellite has possibly become unstable: a) slow
tumbling, b) rapid tumbling.  Iridium satellites that we have identified as
11, 18, 21, 27, 22, 46, and 71 seem to be failed. These numbers are based on
the Iridium numbers listed in the OIG data base. What OIG calls Iridium 20
is apparently the real Iridium 18 (as identified by Iridium LLC) and vice
versa just as Iridium 46 is probably the real Iridium 24 and vice versa.
There are possibly 6 other objects for which the names and identities are
not correct. All this is caused by the movement of the satellites from
engineering to operational orbits and the tracking problems by USSpace
Command when two Iridium satellites in similar orbits pass close to each
other in the sky.  

We are hoping that Iridium will be able to post a comprehensive list that
will let all space trackers know the correct identities in the very near
future. It would hopefully tabulate the satellite number within the
designated plane, the USSpaceCommand catalog number, the international
designator and the common name (e.g. Iridium XX).

The observations that I and others make are strictly our own observations
and opinions based upon the information that we use from OIG (or other
sources). We attempt to be as accurate as we can; however, under the
conditions that exist with satellite maneuvers and with two satellites
passing close to one another on various occasions, it should be expected
that this confusion will continue.  Anyone who may choose to act on any
information posted on this net would be well advised to check and double
check the facts with the posters before jumping to any conclusions.  
Paul D. Maley

tel. 281-244-0208; fax: 281-244-1140
latitude 29.6049 north, longitude 95.1086 west, elev 6m