Why does NASA build in launch countdown holds?

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Offline Eric A. Taylor

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Why does NASA build in launch countdown holds?
« on: 26/11/2009 05:29:14 »
From the time of the Mercury-Redstone flights of Shepherd and Grissom NASA has used a timed countdown to guide what events should take place up to the time they light the engines and release the rocket into orbit. Several holds are built into this countdown in different places. Why? Why not simply make the countdown longer, then hold only when you fall behind? Could it be that NASA doesn't want us to know how often they wold fall behind in the countdown?
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Offline LeeE

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Why does NASA build in launch countdown holds?
« Reply #1 on: 26/11/2009 10:48:08 »
I suspect you've answered your own question; "NASA has used a timed countdown to guide what events should take place up to the time they light the engines and release the rocket".

The holds probably tie in with the events, so if a particular event or condition isn't nominal by the time the corresponding hold point is reached then a hold will be declared.
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Offline Eric A. Taylor

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Why does NASA build in launch countdown holds?
« Reply #2 on: 02/12/2009 00:33:35 »
Most of these built in  holds are for a set period of time. To read the countdown checklist http://science.ksc.nasa.gov/shuttle/countdown/count.html
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