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Re: Another view



Hi Phil,

I didn't realize that you were thinking of a constellation of LEOs. I agree
and this is very feasible with interconnected ground stations for relaying.
The Internet provides a low cost way to do this in the most heavily
populated parts of the world. The launch costs are also spread out so that
they are more easily affordable by AMSAT. In addition, it doesn't
shortchange the Australians.

A constallation starting with 3 or 4 satellites would be valuable for hams
if the orbits are appropriate. We really only require a few hours of access
per day.

The intersatellite links must be digital and user links should be mostly
digital, but a channel or two of NBFM access would provide backwards
compatibility so that no one is left out of phase 4. Right now we have two
classes of satellite users -- those on FM LEOs because of low cost and those
on AO-10 who want to work DX. Almost all of the AO-10 users have
transceivers that support FM so this would allow universal access.

73,

John
KD6OZH

----- Original Message -----
From: "Phil Karn" <karn@ka9q.net>
To: <kb5mu@AMSAT.Org>
Cc: <na9d@mindspring.com>; <amsat-bb@AMSAT.Org>
Sent: Sunday, 24 December 2000 08:07 UTC
Subject: Re: [amsat-bb] 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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