Comment by stetrain

14 hours ago

1 out of the 12 crewed Apollo missions resulted in the death of the crew, so a 1 in 12 effective mortality rate.

Apollo 13 was a very close call. If that had ended in failure the mortality rate would have been 1 in 6.

So 1 in 30 would be a pretty clear improvement from Apollo, and we are a lot better and more thorough at modeling those risks and testing systems than we were during the Apollo program.

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stetrain

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shash  11 hours ago

Is 12 enough of a sample size to make a statistical judgement? What if there were 20 more which didn’t have a loss of life? Is it then 1/30? What if there were 20 more?

The risk factor is calculated _per mission_ from what I understand. You can have three accidents in a row and nothing for decades but the risk itself can still be 1 in 30.

  • the__alchemist  4 hours ago

    Your point is fair and and important distinction. I think when estimating a risk factor though, this empirical data, while a low sample size, is a valuable statistic because it's empirical, and not that small of a sample size. Maybe going forward, we have 3 risk levels:

      - Historical. Low N as you say. (Even though each mission and spacecraft is different and they're spread out over time, there's value in this)
  - Bureaucrat number; absurdly low, but looks good to politicians etc
  - Engineering estimate

  • stetrain  11 hours ago

    So the risk factor for Apollo could have actually been 1/1000 but they were just really unlucky?

    • shash  1 hour ago

      Yes, actually. This is similar to having a 100 year flood five years in a row. It doesn’t mean that the flood occurs only once in 100 years. _On average_ it’s 1/100 probability of occurring in any given year.

      But then, Apollo 1 was after all the first mission on the Saturn V. I think we should assess even its pre-launch risk much higher than the rest of them. Similarly Artemis II has a much higher risk than the subsequent ones will have.

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    • d1sxeyes  5 hours ago

      If I toss a coin four times and it comes up heads three and tails once, it doesn’t mean that there’s a 75% chance that this coin lands heads up. Be careful about conflating risk factor and mortality rate.

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