I know that Merlin is extremely reliable, at least over 99%. I do know of one time when one failed, on Falcon 9's fourth launch. SpaceX had used hundreds, if not thousands, of them. I assume there is enough data to make a reasonable reliability estimate. What would that be?

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    $\begingroup$ It might be useful to quantify 'reliable', it seems like you are using for 'successful payload to orbit' but ground scrubs, landing problems or just start are all valid methods to count. $\endgroup$ Feb 22, 2022 at 12:35
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    $\begingroup$ 142 F9's, 3 F-H;s have flown. That is 142 X 10 enginers per F9 + 28 per F-H = 1504 engine burns. 1 partial failure. 0.06 % failure? So 99.94 success? I dunno, seems pretty good to me. $\endgroup$
    – geoffc
    Feb 22, 2022 at 15:41
  • $\begingroup$ @geoffc: It's not quite that simple. While there have been 145 Falcon 9 second stages, there have only been 72 boosters (and 6 of them haven't flown yet). It is generally not known how many engines there have been. Also, on a single flight, a particular engine may execute between 1 and 4 burns depending on which engine it is and the flight profile. $\endgroup$ Feb 22, 2022 at 15:53
  • $\begingroup$ @JörgWMittag Agreed to all. But I was simply counting # of Merlins used in flights. # of burns/engine (even run time/engine) would be really interesting and only SpaceX likely knows that info. $\endgroup$
    – geoffc
    Feb 22, 2022 at 15:55
  • $\begingroup$ 99 % is not that much when all 28 engines should not fail, the probability of success would be only 75.5 %. If the reliability of one engine is 99.9 %, the result for 28 engines is 97.2 %. For 99.99 % we get 99.72 %. $\endgroup$
    – Uwe
    May 5, 2022 at 9:26


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