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Re: AMSAT NA



----- Original Message -----
From: "Stephen Melachrinos" <melachri@verizon.net>
To: <amsat-bb@amsat.org>
Sent: Friday, July 18, 2008 1:01 AM
Subject: [amsat-bb] Re: AMSAT NA

> The Molniya orbit **is** a HEO, albeit a special one.
>
> http://en.wikipedia.org/wiki/Molniya_orbit
>
> Its characteristics:
>
> - Its apogee is over the North, so it spends most of its time (better than
80%) above the equator.
> - Its period is equal to one-half of one sidereal day, so its ground track
repeats exactly each day.
> - Its inclination (63.4 degrees) is such that its argument of perigee
doesn't shift (from 270 degrees) so the apogee  > -stays over the North
Pole.
>
>
> Steve
> W3HF
>
Hi Steve, W3HF

Here is the problem with the Molniya orbit. Since the inclination is 63.43
degrees then the argument of perigee doesn't shift because the line of the
apsides that join the apogee and perigee do not rotate.
If after launch the argument of perigee is placed to 270 degrees then the
apogee will stay over the Northern emisphere for the full life of the
satellite.

More exactly the latitude of perigee will be:

Latitude of perigee = arc sin ( sin 63.43 x sin 270 ) =  - 63.43 degrees in
the South emisphere

Changing the signe the latitude of the apogee will be + 63.43 degrees in
the Northern emisphere

Forever !

In this conditions the satellite will be not useful for South America ,
South Africa, Australia and so on in the Southern Emispfere.

This is why the Molniya orbit is nice to broadcast TV and make phone
communications for the Russian areas but not for us worldwide.

In addition as soon the Molniya satellite is at the apogee the speed is very
low and the orbit is unstable because it is strongly perturbated by the
forces of the moon and the sun and very soon the perigee will aproach the
earth and the the satellite will be lost.

73" de

i8CVS Domenico





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