Satgen 537  Satellite Height Pt1  by GM4IHJ  (BID SGEN537) 1999-07-10

It is interesting to look back into satellite history and see "How we
did things differently a few years ago ". Almost all the best of the
LEO low earth orbit Amsats and RadioSports , went to much higher
altitude than todays birds. AO6, AO7, and RS1 to 8 inclusive all
orbited above 1500 kms mean altitude. Today almost everything locates
below 750 kms.

The original reason given for coming lower , was that the Van Allen
Radiation Belts - average lowest altitude around 1200 kms, were
affecting satellite life due to radiation damage. . In fact this
really applied to commercial satellites only. There was no sign that
any of the Amsat/RS birds succumbed to radiation damage, with the
singular exception of RS8. The failure mode of the Amsats and RSs was
invariably battery failure , followed in two cases by greatly extended
life on solar cells only. In fact the only reason our satellites have
come lower seems to be that any launch opportunity we get is
invariably to a lower altitude these days because most commercial
satellites are carrying large amounts of microchips and other
components which are suceptible to radiation damage. 

In these lower orbits modern LEO amsats have in most cases less useful
life than the old higher altitude analog amsats, even if one excludes
the fact that modern amsats seem to take years of testing in space
before they are turned over to the amateur radio community. Coming
lower has certainly reduced the incidence of software failure, but
this is a feature of digital satellites with their much greater memory
and processing micro electronics. Software which is simply not
necessary in great quantity in a satellite amateur radio analog
transponder. So perhaps if we could put up a few analog satellites ,
we can safely put them up above 1500 kms ( or at least well above 750
kms).  At which height we will get the benefit of longer times in
range of a particular ground station, and, greater footprint coverage
and hence much enhanced DX capability. For lets not forget that with
Oscar 6 , California was in range of Scotland, whereas todays ground
skimmers get no further from Scotland than a few east coast states.

Is this all a pipe dream. No it is not. Some modern satellites ie
Globalstar are going higher, above 1200 kms, and in a year or two some
of the new communications satellites will be orbiting at intermediate
heights around 24000 kms. So can we hitch a ride. Modern microchips
are much more radiation resistant than the stuff that went into
satellites of yesteryear.

At present there is almost nothing by way of real long range DX for 
the satellite user who wishes to communicate in the normal human way
in real time. Amsat and other satellite builders have for over a
decade focussed on low altitude digital systems. Whatever happens to
Phase 3d we will not be able to afford anything exotic for a long
time. Preparation of a straight forward mode B, J or S analog sat for
an orbit above 1200 kms looks like the only way forward.. It need be
no more complex than Oscar 7 , and it could be operational within a
few days of launch. More discussion on Sat Height next satgen.