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Safety panel raises concerns about Falcon 9 pressure vessel for commercial crew missions
An independent safety panel recommended NASA not certify SpaceX's commercial crew system until the agency better understands the behavior of pressure vessels linked to a Falcon 9 failure in 2016. That recommendation was one of the stronger items in the annual report of the Aerospace Safety Advisory Panel (ASAP) released by NASA Jan. 11, which found that NASA was generally managing risk well on its various programs.
The report devoted a section to the composite overwrapped pressure vessels (COPVs) used to store helium in the second stage propellant tanks of the Falcon 9. The investigation into the September 2016 pad explosion that destroyed a Falcon 9 while being prepared for a static-fire test concluded that liquid oxygen in the tank got trapped between the COPV overwrap and liner and then ignited through friction or other mechanisms.
SpaceX has since changed its loading processes to avoid exposing the COPVs to similar conditions, but also agreed with NASA to redesign the COPV to reduce the risk for crewed launches. NASA has since started a "rigorous test program" to understand how the redesigned COPV behaves when exposed to liquid oxygen, the report stated. ASAP argued that completing those tests is essential before NASA can allow its astronauts to launch on the Falcon 9. "In our opinion, adequate understanding of the COPV behavior in cryogenic oxygen is an absolutely essential precursor to potential certification for human space flight," the report stated, a sentence italicized for emphasis in the report.
[...] The report raised issues in general about the commercial crew program, including concerns that neither Boeing nor SpaceX, the two companies developing vehicles to transport NASA astronauts to and from the International Space Station, will meet a requirement of no greater than a 1-in-270 "loss of crew" (LOC) risk of an accident that causes death or serious injury to a crewmember. That includes, the report stated, a risk of no more than 1 in 500 for launch and reentry.
Both programs are likely to be delayed:
Boeing, SpaceX have razor-thin margins to fly crew missions in 2018
(Score: 0) by Anonymous Coward on Sunday January 14 2018, @10:54PM (6 children)
So the 50/50 odds for a coin toss don't make any sense unless we are going to sit there and flip the damn coin one hundred times? Methinks someone is lacking a basic understanding of probability.
(Score: 4, Touché) by takyon on Sunday January 14 2018, @11:31PM
1. We don't know the real odds before it launches.
2. It won't launch often enough for us to determine the real odds. Space Launch System has 12 planned launches [wikipedia.org] over a 14 year period. Only 7 of them will be crewed, and three of the launches will be on the second main variant of the design, Block 2. There's probably not enough coin flips for disaster to strike.
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(Score: 3, Informative) by khallow on Monday January 15 2018, @12:47AM (4 children)
As to manned space flight, it hasn't happened often enough to bother with a 1 in 500 LOC rate. We've only had 320 crewed launches since the beginning of space exploration. There is no basis for asserting such a high reliability. We could, for example, have several 1 in 500 LOC risks that apply to every manned launch ever made, that just haven't happened yet. In the face of that level of ignorance, it makes no sense to demand high standards of reliability.
(Score: 4, Interesting) by JoeMerchant on Monday January 15 2018, @04:58AM (3 children)
You're right that we're ignorant of the "true" (better stated as "statistically reliable") rates of failure in use: insufficient data.
You're wrong that attempting to design for high standards of reliability is senseless. It's quite expensive to train new astronauts and build replacement vehicles, not to mention politically difficult to fund a program that makes us look foolish and incompetent.
When there's insufficient test-trial data to base failure rate analysis on, the engineers pull numbers out of any convenient orifice and throw them into a risk management table - in med devices there's a whole standardized ISO procedure for doing just that. The "guess" numbers are tossed around between the best experts available until they reach consensus - the process is documented as a design review, and we move on to the next problem. I imagine in NASA's manned programs they include such available data as they have to inform their guesses. You'd be surprised at just how valuable these risk management processes turn out to be, even when the best experts available can't point to massive records of previous experience.
Even the Space Shuttle managed to successfully take off and land in 132 of 134 tries. You don't get to that level of reliability without designing for it.
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(Score: 1) by khallow on Monday January 15 2018, @07:53AM (2 children)
It can be worse than senseless. For example, such design can actually introduce risks that are higher than the ones that the effort is trying to reduce. It can also create moral hazards and other systemic or behavior problems that increase risk.
And having a few dozen manned launches already under one's belt.
(Score: 0) by Anonymous Coward on Monday January 15 2018, @08:40AM (1 child)
Say what?
And you didn't even mentioned ethical hazards.
(Score: 1) by khallow on Monday January 15 2018, @07:02PM