Liftoff of STS-110 in 2002
Liftoff of STS-110 in 2002

The launch of Space Shuttle missions was governed by a countdown. Two clocks were maintained, the unofficial, but sometimes mentioned, L (launch) clock represented the time remaining before the scheduled launch in real time, and the more often referred to T (test) clock included several built-in holds where additional verifications were made. Built-in holds were extended if mission parameters allowed for additional checks or to correct issues. Launches of the Space Shuttle to the International Space Station did not allow for holds to be extended due to the launch window which was limited to no more than 10 minutes due to the 90 minute orbit period of the station and speed of Earth's rotation (913.6 miles per hour (1,470.3 km/h) at the Kennedy Space Center[1]), which puts the launch pads 1,000 miles (1,600 km) east of the station on its next orbit.[2][3][4][5]

Milestones

T−43 hours and counting

T−27 hours and holding

T−27 hours and counting

T−19 hours and holding

This built-in hold typically lasted four hours, but was extended if PRSD offload is required. During this hold:

T−19 hours and counting

T−11 hours and holding

This built-in hold varied between 13 and 14 hours.

T−11 hours and counting

T−6 hours and holding

This built-in hold typically lasted two hours, or one hour for a 24- or 48-hour scrub. Countdown may be resumed at this point after a 24‑hour scrub/turnaround.

T−6 hours and counting

T−3 hours and holding

This built-in hold typically lasted two-and-a-half hours.

T−3 hours and counting

T−20 minutes and holding

This built-in hold typically lasted 10 minutes.

T−20 minutes and counting

T−9 minutes and holding

This was the final built-in hold, and varied in length depending on the mission.

T−9 minutes and counting

T−5 minutes and counting

T−10 seconds and counting

T−0 seconds

References

  1. ^ Butterworth, Paul. "Speed of the Earth's Rotation". NASA.
  2. ^ Adams, Eric (March 2002). "How Things Work: Shuttle Launch Windows". Air and Space. Archived from the original on 2012-07-17.
  3. ^ "LAUNCH COUNTDOWN FOR SHUTTLE MISSION STS-97 BEGINS 1 A.M. NOV. 28". NASA. Archived from the original on 2011-04-16.
  4. ^ "Space Shuttle Launch Countdown". NASA.
  5. ^ "Countdown 101". NASA.
  6. ^ "Space Shuttle Launch Countdown". ksc.nasa.gov. Retrieved 2016-12-09.