How many times have space shuttle launches been scrubbed

How many times have space shuttle launches been scrubbed?

Using the criteria in the summary of space shuttle missions, viz

  • Shifts are defined as start delays that occurred prior to calling stations for the OMI S0007 Shuttle Countdown.

  • Scrubs are changes to the start date after the shuttle countdown has started (the countdown has ended or has been traced back to a later start date).

  • Delays are delays that only occur on the day of take-off.

(Bullets and emphasis mine.) (Pad breaks are counted as peelings.)

I get 121 peels in 135 launch campaigns or a nearly 90% chance of scrubbing. To actually answer the question asked, ~ 1.9 start attempts per mission.

Worst of all were STS-61C and STS-73, each with 6 peels.

The linked document contains some information about each peel.

Note: There is some ambiguity that can change the number of scrubs by some in either case. Mission 51-E was canceled after its launch, and throughout the hydrogen leak fiasco there was a lot of rolling in and out, fueling tests, etc. for missions STS-35 and -38.

Unfortunately, it looks like the track record hasn't really gotten better over time. This shows the number of peels applied against the later start date.

  • A - the best run in the program, 9 consecutive starts without scrubs
  • B - Standstill according to STS-51L
  • C - Standstill according to STS-107