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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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