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From: steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224)
Newsgroups: net.astro
Subject: Re: Launch Window.  What do they mean by this?
Message-ID: <557@jplgodo.UUCP>
Date: Wed, 29-Jan-86 13:03:47 EST
Article-I.D.: jplgodo.557
Posted: Wed Jan 29 13:03:47 1986
Date-Received: Sat, 1-Feb-86 04:39:33 EST
References: <2170@amd.UUCP>
Organization: Jet Propulsion Labs, Pasadena, CA
Lines: 41

> 
> I have been wondering what they mean when they say that the
> Shuttle, or other space vehicle, has missed the launch window.
> Is there a region of space that they need to travel through
> in order to minimize the affects of the Van Allen belts or does
> this term refer to an on ground time table?  Any help on solving
> this question would be appreciated.
> 
> paulw

Launch windows are determined by the type of mission you are trying to fly.
For example, if you are trying to send a spacecraft to Jupiter, there
are a set of optimum dates to leave Earth.  If you tried to leave at some
other date, the launch vehicle you are using couldn't provide the energy it
would take to get to Jupiter.

Another example might be a spacecraft which is to go into an Earth orbit where
it can see the Sun throughout the orbit.  If you launch into a polar orbit
around dawn, this is not too difficult to achieve.  However, if you launch in
the middle of the night, you will need to do something to the orbit after
launch in order to rotate the orbit around to where the spacecraft
can always see the sun--this something takes energy and a lot of it.

The launch window then is the period of time in which it is easiest to
accomplish whatever you are trying to do.  Oftentimes, if you don't go at the
easiest time, you just can't go at all because the available launch vehicles
aren't strong enough or your spacecraft can't tolerate the forces that would be
needed.

Another type of constraint is what is happening at the launch site itself.  At
least in the early shuttle launches, they wanted to be able to watch the launch
vehicle during the boost phase.  This meant that the launches had to happen
during the daylight hours.

Hope this helps,

...smeagol\			Steve Schlaifer
......wlbr->!jplgodo!steve	Advance Projects Group, Jet Propulsion Labs
....group3/			4800 Oak Grove Drive, M/S 156/204
				Pasadena, California, 91109
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