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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: sci.space,sci.space.shuttle
Subject: Re: space news from Aug 24 AW&ST
Message-ID: <8760@utzoo.UUCP>
Date: Tue, 13-Oct-87 15:43:00 EDT
Article-I.D.: utzoo.8760
Posted: Tue Oct 13 15:43:00 1987
Date-Received: Tue, 13-Oct-87 15:43:00 EDT
References: <8727@utzoo.UUCP>
Organization: U of Toronto Zoology
Lines: 24

> ... feasibility study of mobile
> communications satellite system, possibly using Molniya orbits for good
> coverage at high latitudes.

I suppose I should explain this, since some people have asked about the
term.  Clarke (geostationary) orbit is the preferred one for comsats, but
it has problems for ground stations at high latitudes.  Clarke-orbit
satellites are low on the horizon for such stations, and in fact are below
the horizon for stations near the poles.  This causes various problems.

The Soviet solution to this is to use a different orbit for their Molniya
comsats.  The Molniyas are in highly elliptical orbits at high inclinations,
with apogee over the northern hemisphere.  This means that they spend most
of their time moving quite slowly across the northern sky (and incidentally
spend the low-altitude part of their orbits deep in the southern hemisphere,
away from hostile nations).  This isn't as good as Clarke orbit, since the
Molniyas do move and stations need to track them continuously, but for high
latitudes the results are better.  The Soviets do now make some use of
Clarke-orbit comsats as well, but the Molniyas remain important.  There are
a few other users of such orbits as well; I believe one of the upcoming
amateur-radio satellites will use such an orbit.
-- 
"Mir" means "peace", as in           |  Henry Spencer @ U of Toronto Zoology
"the war is over; we've won".        | {allegra,ihnp4,decvax,utai}!utzoo!henry