Space Forum / Space Flight / January 2006

When I worked on Iridium, the last 18 months of its
main software development effort at Motorola, they
were contemplating a 24x7 ground support team of
around 20 individuals. I don't remember if that was
"per shift" or "total", though.

Iridium takes a _tremendous_ amount of tweaking,
since it depends on satellites knowing each others
ephemeris to high accuracy, so the satellite to
satellite laser communications can be kept aimed
accurately, knowledge of the satellites own
ephemeris and changes to it, so the solar panels can
be kept faced toward the sun, so results of
atmospheric drag can be overcome and pitch and yaw
away from the intended orbit due to half a dozen
un-"spherically symmetrical" forces that act on the
satellites can be countered by correcting with
gyroscopes or with steering gases.

Too, the satellites don't last forever, and must be
replaced on a continuing basis. I seem to recall
that the planning included a set of hot spares in
orbit, too.

There are many ground stations, to send control
signals to the satellites, and to provide
connections between the satellites and the local
"POTS" (plain old telephone system) and those, also,
need ongoing maintenance.

All of this means that Iridium would "stop working"
fairly promptly if the ground crew went on strike.

HTH

xanthian.

I haven't a clue about GPS, but some of the same
considerations may apply.