Satgen 621 Iridium Reborn  by GM4IHJ  (BID SGEN621)    2001-02-17

Just as everyone got ready to hold their breath, for the proposed
deorbit of the 87 Low Earth Orbit satellites of the bankrupt Motorola
led satellite phone venture. The unexpected has happened. Whereby the
US Department of Defence has stepped in with a contract proposal
which could lead to in orbit operation until the end of 2004.

The US government has always been a big Iridium user. Owning 3600 of
the bulky handsets. Now they appear to have decided that the new
Iridium satellite company ( successor to Motorola et al ). Will get
them out of a hole, whereby their existing UHF networks are
struggling to copy with user demands.

At present there are 87 of the original 88 satellites still in orbit
. But the operational number is thought to be as low as 67 or 68, ie
only just above the magic figure of 66 said to be necessary for
complete coverage. So it is doubtful whether a full network will
survive until 2004 , unless some new satellites are launched, to fill
gaps as they occur.

Needles to say this is very bad news for Radio Astronomers. The broad
band nature of the individual time division multiplex signals in the
1622 to 1627 MHz band is reported to have been a constant problem for
anyone hoping to study the natural signals in the adjacent Hydroxyl
band. It is also bad news for visual astronomers. Noting that the
reflection of sunlight from the very large solar panels of the
satellites produces a search light beam effect , which sweeps across
the earths surface below, introducing a very bright flash of light,
as its landfall coincides with the position of any astronomer busily
watching something much dimmer. 

In addition to military usage. The Iridium satellite company suggest
that they may market the system to industrial users. They do not
however, propose to open the system up for the use of the general
public.

All should become clear over the next few months. There will be many
former users who will be surprised at this last minute reprieve.
Noting that the existing system is far from perfect. However the
action of the US Department of Defence is understandable. They get a
cheap service to tide them over a problem, and they postpone the
inevitable day when the whole system has to be deorbited. A not
surprising attitude with MIR due to head for a fiery finish around
the 6th of March 2001. If MIR goes wrong, an Iridium deorbit of 87
satellites shortly thereafter would certainly have the whole world
holding its breath. 

So far the European media seems to have forgotten that the last space
station funeral, resulted in a lot of Salyut 7 going far astray. One
big lump finishing up in a South American garden.  Lets hope, MIR is
better behaved, and just as important, US military operators do not
use their handsets too close to radio observers who thought the
Iridium " Menace " had departed.