Posted on 07/16/2019 6:00:11 AM PDT by BenLurkin
... Crew Dragon’s explosion was unrelated to the spacecraft’s propellant tanks, Draco maneuvering thrusters, or SuperDraco abort engines. Rather, the cause lies in a more exotic and unanticipated chemical/material interaction between a plumbing valve, liquid oxidizer, and a helium-based pressurization system.
According to Hans Koenigsmann, SpaceX is approximately 80% of the way through what is known as the fault tree, ….SpaceX executive was fairly confident that the results presented on July 15th would be representative of the final conclusion.
The ultimate (likely) cause of Crew Dragon’s extremely energetic and destructive explosion centers around the spacecraft’s extensive SuperDraco/Draco plumbing and its associated pressurization system, which uses helium to keep the pressure-fed engines, propellant tanks, and feed lines around 2400 psi (16.5 megapascals).
... this method of pressurization means that there is direct contact between the pressurant (helium) and the oxidizer/fuel, thus requiring some sort of valve preventing the pressurized fluid from flowing into the pressurization system.
SpaceX’s understanding is that the high-speed slug of dense NTO was traveling so fast and at such a high pressure that, by impacting the titanium check valve, it quite literally broke the valve and may have chemically ignited the metal, thus introducing a slug of burning NTO into the liberated NTO system itself – effectively a match tossed into a powder keg.
... the solution – as SpaceX perceives it – is the same: instead of a mechanical check valve (simple but still not 100% passive), the barrier between pressurant and oxidizer (as well as fuel, most likely) will be replaced with something known as a burst disk. According to Koenigsmann, only a handful (~4) of those valves exist and thus need to be replaced by burst disks, a relatively fast and easy fix.
(Excerpt) Read more at teslarati.com ...
They look simple, but have to be sized and installed properly. I always installed them in my systems personally. Proper torque and cross pattern tightening is mandatory. Even check valves are subject to pipe thread/dope coming loose and sticking the mechanism open. It’s nice to have accomplished technicians to work with. Some certainly should never be around anything dangerous. Yes, even water systems are dangerous.
bttt
You learn more from failures than you do from successes.
bottom line is that rocket science has always been about blowing shit up until something finally flies ...
My class mate and friend from the Naval Academy died in the Columbia disaster, so don’t think I don’t appreciate efforts to reduce risk.
The space race of the 60’s has a parallel to the call to war in the 40’s. In WWII the government asked industry what it would take to build an air force capable of bombing Germany back to the stone age. Industry told them and the govt paid for what was necessary. It wasn’t cheap.
In the 60’s Kennedy asked what it would take to get to the moon in 10 years and beat the USSR, and then we paid the cost.
Todays motivators are different. Govt doesn’t say to industry we need to do X in Y amount of time. Instead they say do X for Y amount of money, and by the way, govt gets to pick who gets the money and who gets left out based on politics and insiders.
All these companies are in competition, nothing wrong with that. But SpaceX has zero track record for manned space as of today, so its invalid to compare that to the other company’s and NASA’s record, regardless of what that record is.
[[A spark between dissimilar metals caused the Hindenburg fire.]]
It was a bomb in a wristwatch.
NASA is a government bureaucracy that occasionally does space exploration.
Anytime you add extensive layers of bureaucrats to engineering, at best, you get delays & higher costs. When you add politically driven bureaucrats, you get the Challenger disaster.
https://cleantechnica.com/2016/01/31/challenger-disaster-happens-politics-overrides-science/
“We’re seeing more and more science overruled by politics – in climate change, in clean energy, in high-speed rail.
But that’s a formula for disaster – like the Challenger disaster that took the lives of seven astronauts and irretrievably damaged the American space program. Given that it was recently the anniversary of that tragedy, it’s worth recalling how the disaster happened.
It was going to be cold that morning — too cold for the o-rings on the fuel tanks to seal properly. That’s what the engineers told management — over, and over. But the engineers didn’t have the final say. There was pressure from upper management to make sure Challenger went up that day (it might have had something to do with NASA brass wanting to give Ronald Reagan a talking point in his State of the Union speech, scheduled later the same day).
When one of the engineers went home the night before, he told his wife, “I think they are going to kill those astronauts tomorrow.””
Agree on the problem of bad decisions.
Both Challenger and Columbia were victims not of design flaw, but of operating outside of design parameters. I fail to see how SpaceX would be an exception to the bureaucratic failure that led to either of the shuttle failures, since SpaceX is simply the contractor and the missions remain NASA missions. The only difference is that the former missions are history and any SpaceX missions are yet to take place.
PS - The shuttle design was never as ‘safe’ as conventional design with capsule atop booster, but that’s a different discussion. Technically, the shuttle design was sound and technical challenges addressed. Operationally, its limits were exceeded, first by having booster o-ring failures due to temp as you pointed out, and second due to ice damage to the wing tiles for a similar type of oversight.
In January 1986 NASA’s Columbia shuttle exploded on launch because NASA had earlier decreed that asbestos was not a safe material. NASA outlawed the asbestos grease which was used to seal the takeoff engine blast cones. On launch the replacement grease failed, the joints failed, and the shuttle exploded.
In February 2003 NASA’s Challenger shuttle broke apart on reentry because NASA had earlier decreed that the freon used to make polyurethane foam was dangerous to the environment. NASA outlawed the polyurethane foam which NASA formed the shuttle’s foam skin from. The replacement foam proved to be inadequate when the Challenger broke apart.
Challenger was 86, Columbia was 2003, but otherwise, very good explanation in your post.
Thinking about it, I would find it difficult to believe NASA made the environmental decisions in a vacuum, but rather think that was driven by pressures outside of NASA from other government agencies with no skin in the game. NASA should have pushed back though.
NASA’s primary problems since the end of Apollo have been budget. They’ve made many design & program compromises due to continued budget cuts to fund “social justice”.
“But SpaceX has zero track record for manned space as of today, so its invalid to compare that to the other company’s and NASA’s record, regardless of what that record is”
And apparently they are having to learn things the hard way those other organizations already know.
Accepting that space is risky is one thing. Putting materials together that are known to explode is just sloppy. I do aerospace systems engineering for a living. If we blew something up any customer I have ever worked with would have us shot down and be giving us the rectal exam toot sweet. Design reviews and safety analysis should have caught this explosion hazard. That is why we do FHAs and what not.
I use to use commercial aviation as examples doing things better... but ever since Boeing latest stupidity....
They had a check valve, an exotic titanium one, and that’s what failed.
50 years later..... We can’t get into orbit....
>>I would find it difficult to believe NASA made the environmental decisions in a vacuum, but rather think that was driven by pressures outside of NASA from other government agencies with no skin in the game. NASA should have pushed back though.<<
Well yeah. The problem lies with government in general. Governments don’t make decisions based on outcomes, but based on politics. The last several disasters show that government has gotten wary of this reputation, and “privatized” responsibility for their bad decisions.
The shuttle disasters happened because congressional Democrats who held NASA’s purse strings placed pressure on NASA to eliminate asbestose and freon. The Deepwater Horizon oil spill happened after Obama’s Interior Department delegated decisions on casing buffers to drilling companies. The Animas River mine disaster happened after Obama’s EPA gave free reins to its mine cleanup sub-contractor. The Boeing Max disasters happened after Obama’s FAA relaxed oversight on Boeing’s aircraft designers. Then there was the suicidal queer Amtrak train driver who accelerated into a Philadelphia curve.
All of these bad decisions can be attributed to self-serving governmental entities choosing winners from people who are qualified to impress political interests instead of doing their f***ing jobs.
I think your summary is a very good analysis. And you are spot on the govt never accepts the blame, but rather always finds a scapegoat.
I bag of hydrogen can never be made safe.
A single spark from static electricity and kaboom.
I am surprised more of them didn’t blow up
I stand corrected: Those tests preceded NASA’s formation.
I use to use commercial aviation as examples doing things better...
Yeah, me too. Until I became an aviation mech, now I
don’t fly at all.
When nitrogen tetroxide goes wrong, things go BOOM!!!
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