Q: What does the "T" mean during a NASA launch countdown ("T minus 10 ... 9 ... 8 ..."? Also, who has the authority to abort the countdown during a shuttle launch?
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Photo courtesy of NASA Space Shuttle Atlantis launched at 6:13:02 p.m. EST. Feb. 7, 2001. |
A: The "T" in the countdown stands for the launch time -- T zero. This time has been set by the requirements of the individual mission. During the countdown, thousands of engineering parameters in the shuttle are monitored by computers at a rate of hundreds of times per second. If any of these measured parameters gets out of predefined limits, the computer can stop the launch. The person with the final authority to stop and restart the countdown is the launch director, to whom all launch personnel report.
Rick Chappell
Director of Science and Research Communications
Adjunct Professor of Physics
Former NASA Astronaut
-- Compiled by Jessica Hathaway
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