You can either use 14/833 crew positions (individuals flew more than once), or 14/355 actual people who ever flew on the shuttle. You could also use 2/135 missi

You can either use 14/833 crew positions (individuals flew more than once), or 14/355 actual people who ever flew on the shuttle. You could also use 2/135 missions. I suppose an argument could be made for 2/269 as well if you want to count launch and reentry as separate risk events. Source: https://www.space.com/12376-nasa-space-shuttle-program-facts-statistics.html https://www.space.com/12376-nasa-space-shuttle-program-facts...