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A built-in hold is a period in a launch countdown where the countdown clock is stopped. The hold serves as a milestone in the countdown and may be of a fixed or variable duration. Criteria for exiting that hold and restarting the countdown may be based on a fixed time, completion of a checklist of work items, or a go/no-go decision from mission management.
For example, countdowns for space shuttle launches include 7 holds at T-27 hours, T-19 hours, T-11 hours, T-6 hours, T-3 hours, T-20 minutes, and T-9 minutes.
- Evans, Ben (2009). Escaping the bonds of Earth : the fifties and the sixties (Online-Ausg. ed.). Berlin: Springer. ISBN 0-387-79093-4.
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