Xref: utzoo sci.space:4478 sci.space.shuttle:507
Newsgroups: sci.space,sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Shuttle-launched satellites considered unreliable?
Message-ID: <1988Feb3.135506.12818@utzoo.uucp>
Organization: U of Toronto Zoology
References: <217@stcns3.stc.oz>
Date: Wed, 3-Feb-88 13:53:45 EST

> ... Are shuttle-deployed satellites really less
> reliable than rocket-launched ones?  How come?

Note that the original quote said "longer life expectancy", not "higher
reliability".  Barring equipment failures, the lifetime of a comsat is
usually limited by its supply of maneuvering fuel.  (No, it doesn't just
stay where it's put, not in the presence of perturbing factors like the
Moon's gravity and Earth's non-spherical shape.)  Other things being
equal -- they often aren't -- Ariane puts a satellite closer to its final
orbit, meaning that less fuel is needed to get it up there and hence more
is left for station-keeping.  This is not because Ariane is somehow better,
but because Kourou is much nearer the equator than Kennedy.  A satellite
launched from Kennedy starts out in an orbit inclined twenty-odd degrees
to the equator, while launch from Kourou ends up in essentially the plane
of the equator.  Clarke orbit, the destination for most comsats, is in the
plane of the equator.  Plane changes take a lot of fuel.

I don't know for *certain* that this is the underlying reasoning, but I'd
be surprised if it was anything else.
-- 
Those who do not understand Unix are |  Henry Spencer @ U of Toronto Zoology
condemned to reinvent it, poorly.    | {allegra,ihnp4,decvax,utai}!utzoo!henry