leech@zeta.cs.unc.edu (Jonathan Leech) (03/15/89)
In article <256@cbnewsl.ATT.COM> sw@cbnewsl.ATT.COM (Stuart Warmink) writes: >In article <36700005@hcx2> tom@hcx2.SSD.HARRIS.COM 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. On NASA SELECT yesterday morning, the commentator said that the launch window began when the commander was strapped into his seat. -- Jon Leech (leech@cs.unc.edu) __@/ ``Those what cannot remedy the past can pretend to repeal it." - Attributed to Santa Ana by Owl
powi@uhura.cc.rochester.edu (Peter Owings) (03/17/89)
>>>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...
ronbo@vixen.uucp (Ron Hitchens) (03/18/89)
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 <nnn> 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
arg@warwick.UUCP (A Ruaraidh Gillies) (03/21/89)
In article <7230@thorin.cs.unc.edu> leech@zeta.UUCP (Jonathan Leech) writes: >In article <256@cbnewsl.ATT.COM> sw@cbnewsl.ATT.COM (Stuart Warmink) writes: >>In article <36700005@hcx2> tom@hcx2.SSD.HARRIS.COM 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. > > On NASA SELECT yesterday morning, the commentator said that the >launch window began when the commander was strapped into his seat. I'd always assumed that launch windows were to give margins of error for 'mating' of orbits, especially when rendezvous-ing with another satellite. Critical, of course, for interplanetary flight. I guess it's not so important for just putting a few machines up there and taking pictures. Then again, you don't want to collide with OTHER satellites, so you have to make sure you take off within set limits. Fatigue can't play such an important part of it. Remember - the status postings said "Launch window extends until 10:37 EST" or similar - you aren't going to pull the crew in *dead on* 10:37 if they're feeling OK. Maybe some of the crew sleep before lift-off ! :-) +============================================================================+ Contact me on: | Ruaraidh Gillies | "Many men have tried." arg@uk.ac.warwick | 2nd year Comp Sci | "They tried and failed?" or | Warwick University | "They tried and died." arg@warwick.UUCP | Coventry CV4 7AL | (Rev Mother Gaius Helen Mohiam & | Great Britain | Paul Atreides -- Dune) +============================================================================+
henry@utzoo.uucp (Henry Spencer) (03/25/89)
>>>In article <36700005@hcx2> tom@hcx2.SSD.HARRIS.COM writes: >>>>Why do earth orbit missions have launch windows? Since nobody seems to have really answered the original question... (The following ignores some details and fine points for simplicity.) The main constraint on comsat launches is power requirements during the climb to Clarke orbit. To keep the satellite rigid and strong for the final motor firing, solar arrays generally aren't fully deployed during this period. This puts a premium on getting as much sunlight on the arrays as possible. Most satellites (even three-axis-stabilized types) are spin-stabilized during this climb, with the motor pointing along the spin axis and the spin axis lined up for the final motor burn. This fixes the spin axis with respect to the Earth, making it impossible for the satellite to turn to point the solar arrays at the Sun. So the trajectory has to be chosen to put the Sun in the right position. This fixes the trajectory in space; to get the satellite into that trajectory, launching from a rotating Earth, it has to be launched at the right time. A weaker but significant factor in the choice of trajectory is avoiding eclipses by the Earth. This affects even non-spinning satellites. Thermal considerations may be a factor, too, although I'm not sure of this. I think even IUS payloads, which aren't spin-stabilized during climb, in fact are spun very slowly ("rotisserie mode") for temperature control. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
phil@hypatia.rice.edu (William LeFebvre) (03/28/89)
In article <1989Mar24.230920.17804@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >>>>In article <36700005@hcx2> tom@hcx2.SSD.HARRIS.COM writes: >>>>>Why do earth orbit missions have launch windows? >... >The main constraint on comsat launches is power requirements during the >climb to Clarke orbit.... Sunrise and sunset at the abort sites also play a part in calculating the window: sunset at the trans-atlantic abort sites and sunrise at the abort-once-around site(s). William LeFebvre Sun-Spots moderator Department of Computer Science Rice University <phil@Rice.edu>
savage@boulder.Colorado.EDU (Charles L Savage) (03/30/89)
>>>>>In article <36700005@hcx2> tom@hcx2.SSD.HARRIS.COM writes: >>>>>>Why do earth orbit missions have launch windows? One of the major reasons for a launch windows (with at least the shuttle) is that the solid fuel needed for lift off needs to be "recharged" every (I think) four hours. } {@@@}%%%%%%%%%%%%#=======================================================> } savage%alta@boulder.colorado.EDU