[sarex] STS-116 LAUNCH BLOG

Arthur Rowe azrowe80 at verizon.net
Mon Dec 4 17:45:23 PST 2006


NASA's Launch Blog - Mission STS-116

*NASA's launch blog will begin live coverage on Dec. 7, 2006 at 3:30 
p.m. EST. *

*Did you know?*
If the countdown clock reads T-26 hours and counting, that doesn't mean 
the space shuttle will launch in 26 hours. During every space shuttle 
countdown, there are several times when the clock is temporarily 
stopped. These periods are called "built-in holds," and they vary in 
length from as little as 9 minutes to as long as several hours. For this 
reason, hold times must be taken into consideration when watching the 
countdown clock.

The space shuttle team uses built-in holds to synchronize with other 
countdown clocks, monitor weather events, make final adjustments to the 
launch time, and check all systems before proceeding.

During the countdown the liquid oxygen vent on the external tank is 
opened to allow the super-cold liquid oxygen to boil off, thus 
preventing over pressurization while the tank remains near its full level.

Once the space shuttle's on board computers start their terminal launch 
sequence, any problem after that point will require calling a "hold" and 
the countdown recycled to T minus 20 minutes.

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