Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP 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