[harshreality]

I think all the SPOF talk is expectation management in case it fails. It's part space telescope mission, part engineering challenge. Even if the space telescope part fails, the engineering effort that's gone into it means something.

They must've calculated that the overall chance of success, and they have a target, and they met their target. Unfortunately, tests and theoretical modelling have a tendency to not exactly replicate a space environment (or any true production environment), nobody's perfect at anticipating everything, and management has ways of manipulating engineering estimates.

The Space Review [1] quotes NASA as saying there are 344 SPOF. They talk mainly about the sun shield, so that's probably the biggest risk, but consider all of them as about equal...

If each SPOF has a 0.1% chance of failure, net success rate is only 71%. Presumably most of the estimated failure probabilities are less than that, and the sun shield—which probably comprises many of the SPOFs—averages (far?) more than 0.1% per SPOF, because everyone seems to be particularly worried about that working.

I wonder what that figure is. Has it been published anywhere? Dear NASA and ESA, what do your engineers say about overall chance of failure?

[1] https://www.thespacereview.com/article/4303/1