Satgen 218   The Great Mobile Phone Race    by GM4IHJ          29 May 93
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If we are to make progress in Amateur satellite usage, perhaps we should
look at what the opposition (???) is doing. I say opposition kindly,
because many of the professionals concerned are Radio Amateurs. The LEO
Low Earth Orbit is finally getting the commercial attention it deserves,
with at least 5 different groups of firms competing for funds and licenses
to operate global LEO multisat communications networks. Two basic systems
are proposed :-
Type 1 Motorola Iridium a 66 sat system, polar orbits, height 765 kms.
Using a method unique to themselves (so far ), whereby you call or receive
from a sat, and the call is relayed as necessary around the world , sat to
sat , until it reaches the sat above your target. Hugely complex and very
circa 2500 million sterling , expensive.
Type 2 Being used by the other consortia is the much less ambitious " Bent
pipe " system used by the Russian Military com birds which follow my
leader in groups of 6 or 8 per orbit. Lorals Globestar (48 sat),
MatraMarconi Odyssey (12 sat), Pacific Comms Aries (48 sat),and Matra
Fairchild Ellipso (24 sat), propose using this system. You connect to any
overhead sat and it relays you to an in range ground exchange from where
your call goes terrestrially to a ground exchange near your target and is
routed to the target by fixed lines if the target station is fixed, or via
a suitable sat in range of exchange and target, down to a mobile target .
Sats transfer as necessary as one leaves your horizon another joins.
Odyssey and Ellipso will have Elliptical orbits 1/4 or 1/10th the distance
of Oscar 13. Hence smaller sat numbers. Aries sats are LEO
Frequencies suggested are 140 MHz ( not Europe), 1.6 and 2.5 GHz.Iridium
needs a clear frequency .Its modulation (time division multiplex) is not
compatable with other systems (code division multiplex ). All systems will
have voice link capability. Only Ellipso and Aries propose data link
capability. Globstar and Odyssey have GPS navigation trace and report
facilities. All except Odyssey will have radio paging.
At the moment the competition is hotting up to get backers and licenses.
There have been suggestions US Federal Communications Commision could
permit early introduction of system standards which Europe would not
favour. Motorola has breadboard system and application for test launches.
Matra Marconi are presently testing an in orbit experimental sat developed
from University of Surrey birds.
As a radio amateur the points which interest me are :-
1. Motorola - enormously complex hardware and software in each satellite.
2. The other systems using well established "bent pipe" techniques could
be a better bet , because they meet the needs of the "go anywhere" mobile
user, in a simple manner.
3. No one seems to be suggesting any sort of commercial "store and
forward" sats. This surprises me in view of two excellent years of
University of Surrey's 3 flying demonstrators. I would have expected them
to be first choice for business data exchange. Unlike the grandiose
systems proposed here , you can build up store and forward facilities one
satellite at a time. You get operationally useful results right from the
start, and you can improve as and when traffic levels require.
PS. For radio amateurs - Why not Amsats with "through the sat" phone
patch.  Ring your Granny in Galveston .73 de GM4IHJ @ GB7SAN