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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.columbia
Subject: Re: Launch Windows
Message-ID: <5179@utzoo.UUCP>
Date: Wed, 6-Mar-85 16:12:43 EST
Article-I.D.: utzoo.5179
Posted: Wed Mar  6 16:12:43 1985
Date-Received: Wed, 6-Mar-85 16:12:43 EST
References: <225@tellab2.UUCP>
Organization: U of Toronto Zoology
Lines: 24

I'm not an expert on this, but there are at least two reasons why there
are definite launch windows for Clarke ("geostationary") orbit.

First, remember that a satellite in that orbit remains over essentially
the same spot on the equator.  This means that you are not only trying
to get the satellite into that orbit, it has to be in the right *place*
in that orbit.  There are further complications because most of the
launch sites are not on the equator, which means that plane changes as
well as orbital shape changes are needed.

Second, most current satellites do not deploy most of their solar panels
until they are in the final orbit, because the support structures are
not strong enough to survive orbital maneuvering.  This means that the
satellites are very short of power while in transit, and the angle of
the sun with respect to the solar cells is significant.  (Satellites are
often not free to turn to get the best angle, due to things like spin
stabilization and the directions rocket motors point.)  Passing through
the Earth's shadow can also be a problem for a power-starved satellite.

For these (and probably other) reasons, satellite launches most definitely
do have time constraints as well as position constraints.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry