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Re: Preferred Phase 3 Orbits



If you have a mutual window function (such
as Quiktrak does),  you can take the orbit
as it now exists and predict  mutual windows
between stations on opposite sides of the globe
and see exactly the effect Phil is talking about.

We would have had hugely long windows between
cities in the northern hemisphere  while even
being able to have several minutes a day  between
say Perth and East Windsor, NJ.   That is if we
locked the argument of perigee away from 270 deg.
It would have been most interesting to say the least.
Enter say 63 deg inclination and various numbers for
the argument of perigee.

For example,  with 63 deg. inclination and 270 argument
of perigee, the mutual windows between say
East Windsor, NJ  and Moscow or Tokyo are well over half
a day.  Now they are 1/5 of the day or so.  In addition
to this, the sun angles are going to be such that with
the loss of the omni antennas,   we will have long
communication outages due to poor antenna angles,
or forced turn off of transponders.  On the other hand,
more sparsely populated areas get as much coverage
as densely populated areas.  This has been a big
bone of contention with our southern hemisphere friends
for a while.  This is now a moot point.

To me all of this is better than a total loss, but I do wish
we had managed to keep it together.  If wishes were
pennies, we would all be rich.

Bob
N4HY


----- Original Message ----- 
From: "Phil Karn" <karn@ka9q.net>
To: <tosca005@tc.umn.edu>
Cc: <amsat-bb@AMSAT.Org>
Sent: Thursday, January 11, 2001 11:26 AM
Subject: Re: [amsat-bb] Preferred Phase 3 Orbits


> >Why is a highly inclined orbit desirable for a Phase 3 satellite?
> 
> Several reasons:
> 
> A satellite operating primarily at high latitude (which a Molniya
> orbit makes possible) allows a mechanically simpler spacecraft. Its
> antenna beams can parallel to the solar panel surfaces and yet still
> maintain good sun angles while the antennas are pointed at earth.
> 
> Spinning spacecraft in equatorial orbits generally require
> mechanically despun antennas to track the earth. This adds cost and
> complexity and can be unreliable. You also can't fully utilize your
> solar array as only part of it is in sunlight at any moment.
> 
> The trend in commercial geostationary spacecraft is to 3-axis
> stabilized bodies carrying the antennas and electronics, and external
> flat solar "wings" that can be more fully utilized. But the arrays
> still have to mechanically track the sun.
> 
> The AMSAT Phase IV proposal for geostationary orbit resembled P3D
> except the antennas were mounted at right angles, and the solar arrays
> did not deploy. This avoids the despin bearing, but it still has the
> power penalty associated with a cylindrical solar array.
> 
> Visualize AO-40 directly over the north pole, with its solar panels
> deployed and the antennas pointing directly at the earth. No despin
> bearing, and no motors on the solar arrays; it can track the sun by
> simply rolling on its Z axis.
> 
> The other main argument for a high latitude spacecraft is its ability
> to provide direct communications between stations farther apart in
> longitude than is possible with a geostationary satellite. The
> argument is that because most of the earth's population lives in the
> temperate latitudes of the northern hemisphere, a single spacecraft in
> a northern Molniya orbit can better serve them than one in an
> equatorial orbit.
> 
> Phil
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 

----
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