Satgen 574   Iridium R.I.P    by GM4IHJ  (BID SGEN574)   2000-03-25

Service to customers of this illfated satellite mobile phone service,
ceased on Friday 17th March 2000. It is always sad to see an exciting
project fail. But what lessons can we learn from it? Could the
satellites be used by anyone else. The answer seems to be NO. The
satellites are very complex with regular maintenance in orbit costing
about 10 million dollars a month. The 1.6 GHz downlink frequencies
have been the subject of many complaints, with the time division
multiplex modulation and compression being blamed for producing lots
of out of band interference . So the only solution appears to be , de
orbit and destroy the 80 or so satellites, in a safe and orderly
manner.

Why did Iridium fail ? The following lists the most obvious of
possible reasons, amongst many.
1. The competing system ( networks of local terrestrial mobile phones)
has grow far bigger and much more successfully than anything imagined
when Iridium was conceived. Indeed Iridiums conceived niche has
perhaps disappeared forever ?
2. The technical complexity of directly connecting between satellites,
both to pass on a call to a following satellite as its predecessor
went out of user range, and or ground station range. Or, to daisy
chain between satellites to provide long distance links, easy with
sats in the same orbit plane , monstrously difficult with sats in
several different orbit planes.
3. Most Iridium calls were to or from terrestrial fixed home or
business phones. This required ground stations connected to national
networks. The ground stations had to be separately licensed in the
countries concerned. This was Iridiums Achilles heel. Its downlink
frequency was said to interfere in an adjacent radio astronomy band.
So radio astronomers petitioned their goverments not to license
Iridium ground stations until Iridium agreed to a punishing schedule
of switch off at night and at weekends. An impossible imposition on a
24 hour network.

What will be the result of this failure? It is probable that other low
earth orbit satellite mobile phone and internet connection systems
will find it difficult to attract profitable support. Something which
is good news for the companies offering the continuously improving
services to mobile phone and data users from geostationary satellites.
Clearly anyone thinking of introducing a low earth orbit mobile phone
or data satellite system in the next few years will be thinking very
hard before they commit their cash. Particularly when they cannot
expect to attract customers already served by excellent terrestrial
mobile phone networks which already connect to long distance
networks. Indeed their only customers are likely to be the very small
number of travellers who wander far from the beaten tracks.

Meanwhile radio amateurs cannot expect to breath any easier. For while
this failure may have removed some of the threat to their bands from
LEO sats. It simply transfers the threat , whereby encroachment by  
terrestrial radio networks is now likely to increase.