Root Cause of SpaceX Crew Capsule Explosion Found and Is Easily Fixed

The SpaceX crew dragon explosion was caused by a cup of liquid oxidizer leaking and coming into contact with titanium and this reacted explosively.

Data reviews indicate that the SpaceX Crew Dragon explosion occurred approximately 100 milliseconds prior to ignition of Crew Dragon’s eight SuperDraco thrusters and during pressurization of the vehicle’s propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer [fuel]– nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.

SpaceX engineering leader Hans Koenigsmann said it was now increasingly difficult for SpaceX to expect a crewed launch of its new spacecraft in 2019.

SpaceX engineers would isolate the oxidizer from the pressurization system and replace the four titanium valves with a simpler component called a burst disc. The impact on the schedule might be “relatively minor,” but said about 20% of the accident investigation remained to be done and that other documented issues needed to be solved as well.

Boeing and NASA Try to Get Competing Crewed Launch by the End of 2019

Boeing needs to successfully complete its pad abort test and uncrewed flight tests in order for crewed flight to happen in 2019.

The following planning dates reflect updated schedule inputs for Boeing’s test flights as of March 26, 2019.

Test Flight Planning Dates:
Boeing Pad Abort Test: Summer 2019
Boeing Orbital Flight Test (uncrewed): current target working date August 2019
Boeing Crew Flight Test (crewed): current target working date late 2019

23 thoughts on “Root Cause of SpaceX Crew Capsule Explosion Found and Is Easily Fixed”

  1. I often wonder if beverage dispensers might have something to offer. At work, a hot milk chocolate machine dispenses a bit of milk–but then follows it with water to prevent souring. I wonder.

  2. Exactly. And then the problem is that there are extensive fit and leak checks to be done after swapping the disk.

    I keep wondering why they don’t just keep the check valve, but do a gradual, partial pressurization to make sure the system is dry. I suspect that there are two problems with his:

    1) The helium valve may not have a regulator on it, and just slams open for the abort.

    2) There may not be a safe way to take the pressure off the system on-orbit when the SD system is safed.

  3. The real issue with a burst disk system is they can not easily do a static fire before launch that doesn’t involve a lot of work to replace said disk. Sure, NASA wants a fresh D2 every launch, but that doesn’t change things in the grand scheme of things, if they end up using used D2’s for other commercial ISS customers such as Bigelow.

  4. If you’re going to pressurize an MMH or NTO tank, then the pressurant needs to come in contact with the propellant at some point. This is that point.

    The only way to keep the helium and propellant out of direct contact is with a bladder that surrounds the prop. But those are usually used for very low-scale thrusters, and I’m sure the maintenance is a nightmare. SuperDraco doesn’t use this.

  5. I’m not sure that I’d call this “easily fixed”, for several reasons:

    1) The fix is kind of a kludge, in that it puts a hefty servicing load on the system if it gets static-tested.

    2) Burst disks are incredibly reliable, but they’re mostly used for fail-safe pressure-relief systems, where what happens downstream of the burst isn’t very import, because it’s usually just a vent to the outside. In this case, the entire pressure-fed thruster system is downstream. If there’s even a small probability of a fragment coming off of the burst diaphragm, that probability feeds into the reliability of the entire thruster system.

    3) It’s not restartable. That’s not currently a problem, but it would be if SpaceX were ever to use the SD for any kind of high-impulse orbital maneuver.

    4) The NTO/titanium ignition is going to require a pretty thorough reexamination of the entire NTO plumbing system.

    5) Last but hardly least: I’d be surprised if this was the only use of a check valve in the D2, and it would make sense to use the same kind of valve as much as possible. They’re going to have to run the failure trees on all of them and possibly make other mods before return to flight.

  6. Saw a youtube video on it. It was informative. Valves will leak, especially over time and especially if you actually open and close them repetitively.

  7. No, i wasn’t referring to you.

    I’m saying low information decision making is an acceptable part of SpaceX’s culture.

  8. “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). Necessarily, 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.”
    edit: where it leaked
    from MattMusson entry

  9. Color me impressed the Super Dracos were recovered intact–speaks to ruggedness of the thrusters. Second, I’m hoping the high speed camera film will be released when the investigation is final.

  10. It is a very different thing to say that “rockets will never be as safe as modern airliners” or “the BFR will never be as safe as airliners”

    You can point to the development of aircraft, and yes, after several decades and some major redesigns they ended up as the safe and boring transport option we love today.

    But the original WWI era aircraft never became safe. So too, the BFR will always be an early and somewhat risky design, even if it has distant descendants which have been developed to 787 levels.

  11. Who are you accusing of designing by gut feel? Are you saying that SpaceX designs are just pulled out of their arse?

  12. Here is a helpful comment from the forum:
    “It makes sense that SpaceX chose check valves at a time they expected to fire the SuperDracos for each and every landing. With that system now relegated to abort duties alone moving to single-use burst discs is relatively inconsequential.”

  13. No one thinks the rocket option is a replacement for airplanes, it’s only an option.
    If you were around during the early decades of aviation and their contemporaneous rates of mechanical failure, you would have probably said something like “I kind of laugh that the right brothers thinks airplanes will be safe enough to replace sailing ships like the titanic…

  14. Allowing complex decisions to adjudicated by ones digestive tract will more often lead to sub optimal results over system 2 reasoning.

    Low information system 1 thinkers are always in love with the idea that gut thinking is the best approach for systems engineering.

  15. Not enough information.
    Why was a check valve used instead of a rupture disk to begin with?
    The two are not equivalent.

  16. I kind of laugh that Elon thinks BFR will be safe enough to replace airplanes… it’s always the little things like….ohh just a little bit of liquid oxidizer leaking … don’t worry about … rockets are safe… as we strap our selves into a giant pressured fuel tank the size of 10 storie building…. lift off New York to Tokyo…

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