Re: FW: Iridium 21 (97-34E, #24873) -- NO FLARE!

Philip Chien (kc4yer@amsat.org)
Fri, 31 Oct 1997 04:26:25 -0400

Paul Maley wrote:

>>One should not assume that all Iridiums will flare per Rob/Randy's
>>programs. Rather assume that Iridium 21, 11, 27, and 36 which are not in

Tristan Cools said:

>Maybe we should keep a list with operational Iridium satellites.

That's probably a good idea.  As a rule any satellite at operational
altitude is probably stable and a candidate for flares.

If a satellite is in the parking orbit then it can flare (if it's
stabilized) or may not (if there's a problem).

My theory is its possible to get unpredictable flares off of the
non-operational satellites.  After all they've got the same MMA antennas,
just not pointed in a very predictable orientation.

>I think Motorola will de-orbit the Iridium satellites at the end of there
>lifetime.  But these four satellites probably can't be de-orbited since they
>can't be manoeuvred in their operational orbit.

Not necessarily.  It's possible that the satellite can be controllable, but
there's a different reason why it won't enter operation.  Some obvious
possibilities are difficulties extending the solar panels, problems with
the solar array drive electronics, problems with the crosslink
transponders, etc.  Under these circumstances the spacecraft would still be
controlable and - after it's used as a training tool for ground controllers
and no longer a useful orbital asset - could be deorbited.

>So we will have to deal with functional and non-functional Iridium
>satellites.  It should be better to delete Iridium 21,11,27 and 36 from your
>Iridium flare prediction file if you want to have a successful Iridium flare
>prediction.


It's also possible that some of these satellites may be spares remaining in
the parking orbit until they're needed.  It makes sense for the satellite
to remain in the parking orbit since less fuel is expended and it can
easily be put in to any one of the 11 operational positions more quickly
than if the satellite was parked at the operational altitude.

Consider that each Delta lofts 5 Iridium.  Each Proton launches 7.  Each
Long March carries 6.  (note the professional writer's use of a different
verb each time. ;-)

Unless you use a Delta and a Long March to populate an orbital plane there
will be leftovers.  So there are extra satellites every now and then which
have to be placed somewhere.  It's possible that the controllers may deploy
the extendable surfaces to check them out, or keep the satellite in its
launch configuration.  As a guess in a quiescent mode (e.g. transponders
off) the satellite would use little power, so the solar arrays would not
necessarily have to track the sun.

Each Iridium has a planned operational lifetime of 5 years, with enough
propellant for 8 years of operation.  If the satellites are hibernating in
the parking orbits there would be little degradation or propellant use.

These are just my theories, but I may check them out with Motorola.



Philip Chien [M1959.05.31/31.145//KC4YER@amsat.org]