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Re: RE: Another view & possible corrections



Ken's scheme used a 19,000 km orbit so it is at a 20 dB disadvantage.
Martin's plan was to use a 2000 km orbit which gives it most of the
advantages of a LEO.  His contention was that 4 of these satellites gave as
much access time as AO-13 and coverage of over 40 % of the earth
periodically throughout the day. 8 satellites would increase that to over
90%. 4-8 satellites should be within the capabilities of AMSAT over a period
of a few years.

John
KD6OZH

----- Original Message -----
From: "David Reinhart" <wa6ilt@BellAtlantic.net>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, 24 December 2000 15:18 UTC
Subject: [amsat-bb] RE: Another view & possible corrections


> Pardon if this is a duplicate.  My mailer returned an error and I need
> to correct something.  The first attempt cited Ken as the author of the
> paper on a constellation in RS-15 orbits.  It wasn't.  It was Martin
> Davidoff, K2UBC.
>
> But Globalstar uses a large constellation of satellites.  How many?
> Surely the
> logistics and technical challenges to building. launching and
> controlling an
> entire constellation must be equal or greater to that of a single high
> orbit
> satellite?
>
> At the AMSAT symposium in Toronto several years back Ken Ernandes did a
> presentation of the coverage available by a constellation of three
> satellites in
> a RS-15-type orbit.  The percentage of continuous coverage all over the
> world by
> at least one satellite was around 80%, as I recall.
>
> I recall the anticipation about the launch of RS-15 as being right up
> there with
> AO-40.  It was right about this time of year, too.  While the spacecraft
> never
> lived up to our hopes, the orbit was wonderful.  High enough that the
> Doppler
> shift was quite manageable while giving a good footprint, low enough so
> that big
> antennas weren't necessary.
>
> I'm not saying that a new satellite in that orbit should be Mode A
> (though I
> happen to like Mode A) but I think the orbit should be considered.  At
> Portland
> there was a talk about the deployment platform for microsats that
> Stanford is
> developing.  Three cubes can fit in the "launcher" and more than one
> launcher can
> be fitted.  I did some doodling about the power available for a
> spacecraft
> consisting of two units tethered together, each three microsats high,
> and it
> looked pretty good.  One side could hold the IHU and beacon, the other
> the
> transponder.  Both would have batteries that could be charged from the
> solar
> cells on either or both...mmm - call them "pods".  That way if the
> IHU/beacon
> died the transponder could operate autonomously.
>
> Since all surfaces of the pods, except perhaps the end where they
> connect, could
> be covered with solar cells maybe attitude control wouldn't be a big
> issue.
> Could it be spin stabilized around the center of the tether?  The
> relatively
> small cross section would mean that the antennas would be minimally
> blocked
> almost regardless of the attitude.  Maybe put the receive antenna in the
> tether,
> with a  transmit antenna on each end (one beacon, one transponder).
> Could the
> antennas serve as gravity booms as well?
>
> Using this kind of form factor would allow us to use a standardized
> deployment
> system that could be used on a variety of launch platforms thereby
> increasing the
> chances for a ride.
>
> Dave Reinhart
>
> Phil Karn wrote:
>
> > >LEOs lose because you have very limited access times and very limited
> range.
> >
> > When my wife and I were in Greece a few months ago, we made several
> > phone calls through my Globalstar phone. Access time wasn't limited at
>
> > all, and our calls reached all the way to the US. Globalstar certainly
>
> > qualifies as a LEO system.
> >
> > Phil
> >
>
> ----
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