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Re: Another view



>Come on, Phil, you can't be serious in comparing the Globalstar system
>to anything that's remotely within the capabilities of the amateur radio
>satellite community.

The original comment to which I was responding made some blanket
claims about the fundamental limitations of LEO satellites. I was
attempting to elicit the assumptions behind those claims.

A Globalstar satellite in LEO has the same geometric limitations as
any other satellite in the same orbit, including amateur. Even the
path losses are approximately the same as a hypothetical amateur
L/S-band LEO satellite.

That leaves the likely higher EIRP of Globalstar, the likely greater
capacity of a Globalstar satellite (due to multiple beams) and
satellite availability with the likely smaller size of an amateur LEO
constellation. Let's address each in turn.

The lower EIRP of the amateur L/S LEO satellite will admittedly
require ground antennas larger than those on a Globalstar phone, but
still well within limits for a transportable station. Certainly much
smaller than an AO-40 class station, so I don't think that was an
issue.

The smaller capacity of the ham satellite is not likely to matter
unless we are *very* successful. I would like to have this become a
problem, just as Globalstar would like to have the limited capacity of
their satellites become a problem. :-)

As for the number of satellites in the constellation, we need to know
not only the fraction of time that each LEO satellite can be seen from
a given point on the earth as compared to a spacecraft in a P3D-like
orbit, but also how many LEO spacecraft could could be built and
launched for the cost of each large P3D-class spacecraft.

The fact that two separate commercial LEO constellations have been
built implies that at least two sets of systems people felt that doing
it that way had some advantages over using fewer spacecraft in higher
orbits.  And that's the real point I have been trying to make.
(Before you mention it, the fact that neither system is making money
doesn't necessarily refute the LEO approach. It's quite likely that
doing it from high altitude would have fared even worse.)

>You also know as well as I do that your calls reached the U.S. on
>landlines, not on the satellite system at all.

Of course. Is landline relay something that can't also be done with
amateur LEOs? Or is that too offensive to the purists? How about
ground stations that relay between different LEO satellites in view at
the same time?

Phil



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