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Feynman's actually observations are well worth reading for anyone who builds anything that may be vaguely considered engineering. http://science.ksc.nasa.gov/s

Feynman's actually observations are well worth reading for anyone who builds anything that may be vaguely considered engineering. http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/roger... The key items for me were: 1) While they had no expectation of erosion, and the design did not call for the o-rings to erode, once they observed them eroding, they retroactively invented a "margin of error" based on what fraction the o-rings eroded. This was not based on an actual understood process, and is akin to saying "well, the bridge didn't break when we drove that truck over it, so it must be okay" 2) The engineers actually knew the risk (~1% chance of loss per launch, not specific to the o-rings, compared with two actual losses of the shuttle over ~130 missions). Management used entirely invented numbers for the risk which were not justified.

JohnJamesRambo 10y ago
Since 1 part in 100,000 would imply that one could put a Shuttle up each day for 300 years expecting to lose only one, we could properly ask "What is the cause of management's fantastic faith in the machinery?" I wonder if you told the management that, in those words, if they would have still believed such a ludicrous idea.
smallnamespace 10y ago
There's a lot of blame that (deservedly) gets pinned on the NASA administrators, but this fails to ask the really important question -- what sort of political and other pressures were put on the administrators such that they felt compelled to make shit up? Seems like it was politically impossible for NASA to say outright that there was a 1% chance of failure for every launch -- it would have led to loss of public support for the Shuttle program. So we have a systems failure where both politicians and the public contributed by making NASA admins feel compelled to lie and cover up to make the launches work. I mean, the courageous thing to do would be to stand up and say space travel is inherently risky, people might die, but it's still worth it. But courageous politicians regularly get voted out of office, and I would bet a courageous NASA admin who said that would end up fired.
- nemild 10y ago
  You're absolutely right, but after so much success there also seems to be a fair amount of confidence/arrogance that set in at NASA regardless of other pressures. Additionally, when you have a civilian on board, I think it really changes how you think about what an appropriate level of risk is (13% might have been ok with professional astronauts who knew the risks beforehand, but likely was too high for a civilian). And the line engineers at Morton Thiokol fought back pretty hard on the decision, even if it might have impacted their careers negatively.
  - vkou 10y ago
    At that point in space exploration, 13% was way too high a risk, even for professional astronauts.
avar 10y ago
Your paraphrasing of Feynman's bridge quote is inaccurate. From Appendix F[1] of the report: [..] In spite of these variations from case to case, officials behaved as if they understood it, giving apparently logical arguments to each other often depending on the "success" of previous flights. For example. in determining if flight 51-L was safe to fly in the face of ring erosion in flight 51-C, it was noted that the erosion depth was only one-third of the radius. It had been noted in an experiment cutting the ring that cutting it as deep as one radius was necessary before the ring failed. Instead of being very concerned that variations of poorly understood conditions might reasonably create a deeper erosion this time, it was asserted, there was "a safety factor of three." This is a strange use of the engineer's term ,"safety factor." If a bridge is built to withstand a certain load without the beams permanently deforming, cracking, or breaking, it may be designed for the materials used to actually stand up under three times the load. This "safety factor" is to allow for uncertain excesses of load, or unknown extra loads, or weaknesses in the material that might have unexpected flaws, etc. If now the expected load comes on to the new bridge and a crack appears in a beam, this is a failure of the design. There was no safety factor at all; even though the bridge did not actually collapse because the crack went only one-third of the way through the beam. The O-rings of the Solid Rocket Boosters were not designed to erode. Erosion was a clue that something was wrong. Erosion was not something from which safety can be inferred. His point about NASA's nonsensical use of the "safety factor" is not that you could drive over a bridge, and look, it didn't break, so it must be OK! It's even worse, you drive a truck over it, afterwards 1/3 of the steel is cracked, so you conclude that it must be able to safely accept 3x the weight. Nonesense! This is the sort of moronic engineering that killed the crew of the Challenger. 1. http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/roger...
- masklinn 10y ago
  > This is the sort of moronic engineering that killed the crew of the Challenger. Note that it wasn't even engineering, reading the story in full (it's great, and covers the software side for which Feynman had nothing but praise) Feynman repeatedly noted that engineers were fairly realistic[0] and had been ringing alarms pretty much all along, this was entirely manglement mangling. [0] unless the spectre of manglement was involved, at least for some of them

JohnJamesRambo 10y ago

Since 1 part in 100,000 would imply that one could put a Shuttle up each day for 300 years expecting to lose only one, we could properly ask "What is the cause of management's fantastic faith in the machinery?" I wonder if you told the management that, in those words, if they would have still believed such a ludicrous idea.

smallnamespace 10y ago

There's a lot of blame that (deservedly) gets pinned on the NASA administrators, but this fails to ask the really important question -- what sort of political and other pressures were put on the administrators such that they felt compelled to make shit up? Seems like it was politically impossible for NASA to say outright that there was a 1% chance of failure for every launch -- it would have led to loss of public support for the Shuttle program. So we have a systems failure where both politicians and the public contributed by making NASA admins feel compelled to lie and cover up to make the launches work. I mean, the courageous thing to do would be to stand up and say space travel is inherently risky, people might die, but it's still worth it. But courageous politicians regularly get voted out of office, and I would bet a courageous NASA admin who said that would end up fired.

nemild 10y ago
You're absolutely right, but after so much success there also seems to be a fair amount of confidence/arrogance that set in at NASA regardless of other pressures. Additionally, when you have a civilian on board, I think it really changes how you think about what an appropriate level of risk is (13% might have been ok with professional astronauts who knew the risks beforehand, but likely was too high for a civilian). And the line engineers at Morton Thiokol fought back pretty hard on the decision, even if it might have impacted their careers negatively.
- vkou 10y ago
  At that point in space exploration, 13% was way too high a risk, even for professional astronauts.

avar 10y ago

Your paraphrasing of Feynman's bridge quote is inaccurate. From Appendix F[1] of the report: [..] In spite of these variations from case to case, officials behaved as if they understood it, giving apparently logical arguments to each other often depending on the "success" of previous flights. For example. in determining if flight 51-L was safe to fly in the face of ring erosion in flight 51-C, it was noted that the erosion depth was only one-third of the radius. It had been noted in an experiment cutting the ring that cutting it as deep as one radius was necessary before the ring failed. Instead of being very concerned that variations of poorly understood conditions might reasonably create a deeper erosion this time, it was asserted, there was "a safety factor of three." This is a strange use of the engineer's term ,"safety factor." If a bridge is built to withstand a certain load without the beams permanently deforming, cracking, or breaking, it may be designed for the materials used to actually stand up under three times the load. This "safety factor" is to allow for uncertain excesses of load, or unknown extra loads, or weaknesses in the material that might have unexpected flaws, etc. If now the expected load comes on to the new bridge and a crack appears in a beam, this is a failure of the design. There was no safety factor at all; even though the bridge did not actually collapse because the crack went only one-third of the way through the beam. The O-rings of the Solid Rocket Boosters were not designed to erode. Erosion was a clue that something was wrong. Erosion was not something from which safety can be inferred. His point about NASA's nonsensical use of the "safety factor" is not that you could drive over a bridge, and look, it didn't break, so it must be OK! It's even worse, you drive a truck over it, afterwards 1/3 of the steel is cracked, so you conclude that it must be able to safely accept 3x the weight. Nonesense! This is the sort of moronic engineering that killed the crew of the Challenger. 1. http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/roger...

masklinn 10y ago
> This is the sort of moronic engineering that killed the crew of the Challenger. Note that it wasn't even engineering, reading the story in full (it's great, and covers the software side for which Feynman had nothing but praise) Feynman repeatedly noted that engineers were fairly realistic[0] and had been ringing alarms pretty much all along, this was entirely manglement mangling. [0] unless the spectre of manglement was involved, at least for some of them