Path: utzoo!attcan!uunet!lll-winken!csd4.milw.wisc.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!vixen!ronbo From: ronbo@vixen.uucp (Ron Hitchens) Newsgroups: sci.space.shuttle Subject: Re: Why are there launch windows? Message-ID: <257@vixen.uucp> Date: 18 Mar 89 07:12:59 GMT References: <36700005@hcx2> <256@cbnewsl.ATT.COM> <7230@thorin.cs.unc.edu> <1124@ur-cc.UUCP> Reply-To: ronbo@vixen.UUCP (Ron Hitchens) Organization: My House, Austin TX Lines: 31 In article <1124@ur-cc.UUCP> powi@uhura.cc.rochester.edu (Peter Owings) writes: >>>>Why do earth orbit missions have launch windows? >>>Crew fatigue is certainly a factor, lying on your back for a few hours can't >>>be all that good for the crew - pretty boring at best. > > Actually I believe there is a launch window because you must >launch at a specific time in order to obtain to required orbit for >whatever the mission requires. > Peter... There are many factors which determine a launch window, even if the particular mission being flown doesn't impose any special constraints. Two major factors I know of are daylight at the emergency landing sites and maximum hold times of various onboard systems. Launches are generally done early in the morning because it's still midday in Europe which is the trans-Atlantic abort site. If they wait longer than about noon or so, it's starting to get dark over there. Many of the onboard shuttle systems, especially the volitile fuel systems, cannot be held for longer than a certain amount of time once they've been activated. If you listen to commentator-critters during a launch, and if they know what they're talking about, they may say something to the effect of "If the launch doesn't go in the next minutes, they'll have to postpone until tomorrow". This is so that those volitile systems can be re-cycled (which can take many hours). Those are only two of the major things I know of, I'm sure there are a bizillion other things that have to be taken into account. Ron Hitchens ronbo@vixen.uucp hitchens@cs.utexas.edu