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Posting-Version: version B 2.10.2 9/18/84; site petrus.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!petrus!karn
From: karn@petrus.UUCP
Newsgroups: net.columbia
Subject: Re: Launch Windows
Message-ID: <306@petrus.UUCP>
Date: Thu, 7-Mar-85 11:16:03 EST
Article-I.D.: petrus.306
Posted: Thu Mar  7 11:16:03 1985
Date-Received: Fri, 8-Mar-85 04:54:40 EST
References: <225@tellab2.UUCP> <218@pyramid.UUCP>
Organization: Bell Communications Research, Inc
Lines: 22

> Shuttle launches have windows because if their launching a geo-stationary
> satelite which orbits over the same spot over earth the have to enter orbit 
> at the right spot over earth.

Not exactly. As the earth rotates, it carries the "target point" AND
the launch site with it, so you could launch at any time and still reach
the desired spot by flying the same trajectory.

The reason you have "launch windows" for geostationary missions is because
the spacecraft must be pointed in a different direction during the orbit
maneuvers and the climb to geostationary altitude, and the resulting sun
angles may be unacceptable if the launch were to take place at certain times.

Depending on the mission, there may be additional constraints on launch
time. In a rendezvous mission you must launch as the launch site
passes through the orbital plane of the target. There may be sunlight
and visibility requirements at various places (at emergency landing sites
for the shuttle, at observation targets for weather and spy satellites,
landing sites on the moon, etc) which all combine to produce a set of
acceptable launch times.

Phil Karn