alt Hacker News> Orion utilizes two Vehicle Management Computers, each containing two Flight Control Modules, for a total of four FCMs. But the redundancy goes even deeper: each FCM consists of a self-checking pair of processors.
Who sits down and determines that 8 is the correct number? Why not 4? Or 2? Or 16 or 32?
Replies
croisillon • yesterday at 9:25 PM
Eight shall be the number thou shalt count, and the number of the counting shall be eight. Nine shalt thou not count, neither count thou seven, excepting that thou then proceed to eight.
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nine_k • yesterday at 7:48 PM
Given a list of estimates of failure probabilities, finding the right mix of redundancy becomes a very tractable problem, maybe even freshman-level.
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They probably set an acceptable total loss rate for the mission and worked backwards to determine how many replicas of each system they need to achieve that while minimizing total cost/weight.
So the answer is "some engineers sat down after talking to management".