To: Jed A1
“The system would have to have a reliability of one! Get real. Tell me a system that is that reliable”.
Response:
You have made my point. Engineers have yet to design anything that has a reliability of 1 with the exception of an un used anvil but even that would eventually fail long before reaching one billion hours. In the case of the explosive bolts there would have to be multiple redundancy within the firing circuits and a means of testing the circuit prior to flight. The conventional thinking in the field of reliability and safety is if something has not failed in the first hour of operation then it should not fail in the second hour or the third and every hour after that until it reaches the limitation of 1 10-9 and at that time it is predicted to fail. If one of the elements fails prior to 1 10-9 then the next failure can not occur prior to the expiration of one billion hours of operation.
Take the Ballistic Missile Defense System proposed by Dubyah. This system has to have a reliability of 1 otherwise a ballistic missile could impact Los Angeles or New York. It must also hit the target with its’ high powered LASER because if it is off by a 10th of a degree it could turn a lot of people on earth to toast. The system is made up of millions of parts and must have multiple redundancy in order to reach the reliability goals but this design concept is yet to turn out a device that has a reliability of 1. When the blades are commanded to blow off then they must blow off otherwise all is lost. The same goes for the interception of a ballistic missile or a reentry vehicle.
“Ordinary ejection seats aren't. That is why they have canopy breakers on the top in case the MDC fails to shatter the canopy or the canopy fails to jettison. . .A helicopter system could have that kind of redundancy i.e. a way of going through the blades if they fail to come off”!
Response:
The canopy breakers are worthless if the seat does not fire. The canopy breakers are there because the designers can’t guarantee that the explosive charges will work or the canopy does not jettison because of a reliability and safety related failure.
Here is an example. The Saturn IVB (the upper stage on the Saturn Apollo boost vehicle) was predicted to have a reliability of 5 Sigma or .99999 where perfect is .999999999999. Even with this high reliability Douglas only predicted a confidence factor of 70% that it would achieve the goal of 5 Sigma. That was the highest. Just think about the two stages below the S IVB. The only people not in attendance when these figures were being discussed were the Astronauts.
A point to ponder: 1 10 9=114,155.25 years.