yee@trident.arc.nasa.gov (Peter E. Yee) (04/23/91)
SPACE SHUTTLE MISSION STS-39 COUNTDOWN STATUS --- April 22, 1991
LAUNCH MINUS ONE DAY
Work at pad 39-A continues to go smoothly today as launch
team members press toward launch of the Space Shuttle Discovery
on Mission STS-39 at 7:05 a.m. Tuesday, April 23. The launch
window extends through 10:31 a.m.
Mission STS-39 is an unclassified Department of Defense
mission featuring two primary payloads: Air Force Program 675 and
the Strategic Defense Initiative's Infrared Background Signature
Survey. There are also two secondary payloads; Space Test Payload
and a Multi-Purpose Experiment Canister.
The countdown clock entered the T-11 hour planned built-in
hold this morning at 4:45. The clock will continue to hold until
resuming the count at 4:45 p.m. today.
Yesterday, the Power Reactant and Storage Distribution
System on-board storage tanks were serviced with liquid hydrogen
and liquid oxygen reactants. Following PRSD loading, the orbiter
midbody umbilical unit was retracted. Communication activation
checks then commenced at about 9:00 p.m. last night.
The Rotating Service Structure is scheduled to be moved away
from the vehicle at 11:45 a.m. today. Also today, final crew
equipment and time critical items will be stowed on the orbiter.
At 7:45 tonight the pad will be cleared of all personnel.
Then at 10:45 p.m., operations will begin to load the external
tank with liquid hydrogen and liquid oxygen propellants. Tanking
operations should be completed by 1:45 a.m. Tuesday.
The seven member STS-39 flight crew, already split into two
teams to accommodate a 24-hour in-flight work schedule, are today
undergoing weather and systems briefings. Tomorrow for launch,
the crew will be awakened at 2:10 a.m. for breakfast. They will
have a final weather briefing, suit up and at 3:50 a.m. depart
their crew quarters for pad 39-A.
The forecast weather for Tuesday's liftoff shows a 60
percent chance of violating launch constraints at the opening of
the window. There is a 50 percent chance of violating constraints
throughout the entire three-hour, 26-minute window. A front
located through western Florida and into the Gulf could produce
low clouds and favorable conditions for thundershowers.
Wednesday's forecast calls for a 40 percent chance of
violating launch constraints; Thursday's forecast calls for a 30
percent chance of violation.rose@beowulf.ucsd.edu (Dan Rose) (04/23/91)
yee@trident.arc.nasa.gov (Peter E. Yee) writes: > The countdown clock entered the T-11 hour planned built-in > hold this morning at 4:45. The clock will continue to hold until > resuming the count at 4:45 p.m. today. This may be a naive question, but . . . Why do they have these planned countdown holds? Maybe "countdown" has a more specific meaning to NASA than it does to me, but it seems like there's no sense in starting a countdown until it's, well, time to count down. -- Dan Rose drose@ucsd.edu
pstinson@pbs.org (04/23/91)
In article <rose.672376814@beowulf>, rose@beowulf.ucsd.edu (Dan Rose) writes: > yee@trident.arc.nasa.gov (Peter E. Yee) writes: > >> The countdown clock entered the T-11 hour planned built-in >> hold this morning at 4:45. The clock will continue to hold until >> resuming the count at 4:45 p.m. today. > > This may be a naive question, but . . . Why do they have these planned > countdown holds? As a hedge against the unexpected. If for whatever reason the countdown work falls behind schedule and there are no built-in holds, you are facing a definite scrub situation. These "built-in" holds allow you to catch up or trouble shoot and still make the target launch time. Unfortunately, sometimes this "extra" time is not enough and you have to scrub anyway.
henry@zoo.toronto.edu (Henry Spencer) (04/23/91)
In article <rose.672376814@beowulf> rose@beowulf.ucsd.edu (Dan Rose) writes: >This may be a naive question, but . . . Why do they have these planned >countdown holds? Maybe "countdown" has a more specific meaning to >NASA than it does to me, but it seems like there's no sense in starting >a countdown until it's, well, time to count down. Well, the reason for having pauses in the sequence is to give some slack in case minor problems develop (which does happen with some frequency). However, it is basically a NASA quirk that the clock stops during these planned pauses. They could just as easily be figured into the official clock time. -- And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology "beans are more important". | henry@zoo.toronto.edu utzoo!henry
mvk@aix01.aix.rpi.edu (Michael V. Kent) (04/24/91)
In article <1991Apr23.133522.21767@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <rose.672376814@beowulf> rose@beowulf.ucsd.edu (Dan Rose) writes: >>This may be a naive question, but . . . Why do they have these planned >>countdown holds? Maybe "countdown" has a more specific meaning to >>NASA than it does to me, but it seems like there's no sense in starting >>a countdown until it's, well, time to count down. > >Well, the reason for having pauses in the sequence is to give some slack >in case minor problems develop (which does happen with some frequency). >However, it is basically a NASA quirk that the clock stops during these >planned pauses. They could just as easily be figured into the official >clock time. Not to correct the famous Henry Spencer :) but I believe the holds are there on purpose. The reason is that it is psychologically easier to extend a planned hold than to stop the countdown in progress. -- Michael Kent mvk@itsgw.rpi.edu McDonnell Douglas Rensselaer Polytechnic Institute St. Louis, Missouri Troy, New York Apple II Forever!
pjs@euclid.jpl.nasa.gov (Peter Scott) (04/24/91)
In article <aysgnza@rpi.edu>, mvk@aix01.aix.rpi.edu (Michael V. Kent) writes: > In article <1991Apr23.133522.21767@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: > >In article <rose.672376814@beowulf> rose@beowulf.ucsd.edu (Dan Rose) writes: > >>This may be a naive question, but . . . Why do they have these planned > >>countdown holds? > > > >Well, the reason for having pauses in the sequence is to give some slack > >in case minor problems develop (which does happen with some frequency). > >However, it is basically a NASA quirk that the clock stops during these > >planned pauses. They could just as easily be figured into the official > >clock time. > > Not to correct the famous Henry Spencer :) but I believe the holds are there > on purpose. The reason is that it is psychologically easier to extend a > planned hold than to stop the countdown in progress. I believe that there is also a second clock running during the countdown that has holds figured into it, and therefore does not stop. I heard them mentioning it during a launch sequence once, but I forget what it was called. -- This is news. This is your | Peter Scott, NASA/JPL/Caltech brain on news. Any questions? | (pjs@euclid.jpl.nasa.gov)
jabishop@uokmax.ecn.uoknor.edu (Jonathan A Bishop) (04/25/91)
pjs@euclid.jpl.nasa.gov (Peter Scott) writes: [Discussion of planned holds] >I believe that there is also a second clock running during the >countdown that has holds figured into it, and therefore does not stop. >I heard them mentioning it during a launch sequence once, but I forget >what it was called. Above the center screen at Mission Control are several clocks. One is labeled "L-". When I last visited the control center in May, the countdown for Astro-1 was proceeding, and the "L-" and "T-" clocks were staggered appropriately. -------- jabishop@uokmax.ecn.uoknor.edu "I'm with you, LEM, though it's a shame that it had to be you. The mother ship is just a blip from your train made for two. I'm with you, boys, so please employ just a little extra care. It's on my mind, I'm left behind when I should have been there." --Jethro Tull, "For Michael Collins, Jeffrey, and Me"
cjs@sppy00.UUCP (SCHALLER CHRIS) (04/26/91)
In article <rose.672376814@beowulf>, rose@beowulf.ucsd.edu (Dan Rose) writes: > yee@trident.arc.nasa.gov (Peter E. Yee) writes: > > > The countdown clock entered the T-11 hour planned built-in > > hold this morning at 4:45. The clock will continue to hold until > > resuming the count at 4:45 p.m. today. > > This may be a naive question, but . . . Why do they have these planned > countdown holds? Maybe "countdown" has a more specific meaning to > NASA than it does to me, but it seems like there's no sense in starting > a countdown until it's, well, time to count down. > -- The purpose of the built in countdown holds are to give the various launch teams, time to catch up, coordinate, and syncronize. At any time during a launch countdown, there seems to be a million things going on at once. If youve ever watched a launch on Nasa select TV, you can listen to the conversations between the people in the lauch control room talking to the astronauts on the shuttle, the payload people, the weather people, the people at mission control, the people feuling the ET etc, ect. You get the idea that theres a hell of alot going on. At some point there might be a function that is taking a little more time than usual, if you are on a strait countdown, you couldnt allow for that extra needed time. The built in hold gives everyone time to complete operations to a point where the groups (teams) can be polled one by one to verify their readyness to proceed with the count.
garym@telesoft.com (Gary Morris @wayward) (04/27/91)
In <1991Apr24.163541.21584@elroy.jpl.nasa.gov> pjs@euclid.jpl.nasa.gov (Peter Scott) writes: >In article <aysgnza@rpi.edu>, mvk@aix01.aix.rpi.edu (Michael V. Kent) writes: >> In article <1991Apr23.133522.21767@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >> >In article <rose.672376814@beowulf> rose@beowulf.ucsd.edu (Dan Rose) writes: >> >>This may be a naive question, but . . . Why do they have these planned >> >>countdown holds? >> > >> >Well, the reason for having pauses in the sequence is to give some slack >> >in case minor problems develop (which does happen with some frequency). >> >> Not to correct the famous Henry Spencer :) but I believe the holds are there >> on purpose. The reason is that it is psychologically easier to extend a >> planned hold than to stop the countdown in progress. >I believe that there is also a second clock running during the >countdown that has holds figured into it, and therefore does not stop. >I heard them mentioning it during a launch sequence once, but I forget >what it was called. There are two clocks running the L- (L minus) and T- (T minus) clock, one stops during holds the other includes planned holding time, but I get them mixed up :-) I think T- is the time remaining not counting any holds, and L- is the time to launch assuming scheduled hold time. The reason for scheduled holds is to have everything in a known state that can stay that way for a period of time to allow for fixing problems. Most of the schedules/checklists are written using T- time so that you can tell exactly where you are supposed to be irregardless of how long the scheduled holds have been. When you get to a hold point, you usually don't want various people to go on to the next steps until everything else is ready. There are time limits on many things, for example you wouldn't want to start the APUs (which can only run for a few minutes before you have to start over) while you are working out a problem somewhere else. In general, when you go past a hold point, you have a certain amount of time in which to launch or you have to scrub until the next day (or move back to an earlier hold point), you want to make sure everything is ok so far before leaving a hold. --GaryM -- Gary Morris Internet: garym@telesoft.com KK6YB (was N5QWC) UUCP: ucsd!telesoft!garym TeleSoft, San Diego, CA, USA Phone: +1 619-457-2700