Quantification of reliability and risk of entire systems like spacecrafts is a real activity in aerospace engineering (probably in other safety critical fields

Quantification of reliability and risk of entire systems like spacecrafts is a real activity in aerospace engineering (probably in other safety critical fields too). They take the reliability figures of every single component based on experience, and use them to progressively calculate the reliability up to subsystem and full system levels. From this, they can assess the probabilistic risk involved. Granted that these figures are theoretical and probably varies from reality by a good margin. But these figures are still useful. For one, these figures are updated, recalculated and refined as more actual figures are obtained from components, packages, subsystems and system level tests. The final reliability and risk figures progressively approach the actual values as more tests, including flight tests are conducted. In addition, even preliminary figures help you identity potential risks and mitigate them with better engineering margins, redundancy, better test methodologies, etc. In other words, the quantification helps you contain the risks much better than any qualitative analysis. In this particular instance, NASA's statement is concerning because it would mean that they don't the reliability figures for many components and/or don't have the reliability assessments based on tests. [1] https://ntrs.nasa.gov/api/citations/20150002964/downloads/20150002964.pdf https://ntrs.nasa.gov/api/citations/20150002964/downloads/20...