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SPACE X release partial explanation of Crew Dragon explosion in April

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posted on Jul, 16 2019 @ 09:31 AM
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SPACE X has released a partial explanation of the April Crew Dragon accident during ground test of the Super Draco thrusters


www.teslarati.com...

In summary there was a leak of Nitrogen Tetroxide (shorthanded as NTO) into helium pressurization line

When high pressure helium was introduced to pressurize the fuel/Oxidizer tanks, a slug of NTO smashed into the titanium check valve
blowing the valve apart and sparking a fire in the titanium valve

SPACE X said will replace the mechanical check vales with simpler burst diss to prevent future occurrences




posted on Jul, 16 2019 @ 09:57 AM
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a reply to: firerescue
Replacing a check valve with a burst disk?
Something doesn't sound right about that answer.



posted on Jul, 16 2019 @ 10:30 AM
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originally posted by: butcherguy
a reply to: firerescue
Replacing a check valve with a burst disk?
Something doesn't sound right about that answer.

What doesn't sound right? They both serve the same function. SpaceX, which is focused on reusability, initially went with check valve that doesn't need to be replaced after use. The burst disk eliminates any possibility of backflow, but will need replacement if used.



posted on Jul, 16 2019 @ 11:30 AM
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originally posted by: nataylor

originally posted by: butcherguy
a reply to: firerescue
Replacing a check valve with a burst disk?
Something doesn't sound right about that answer.

What doesn't sound right? They both serve the same function. SpaceX, which is focused on reusability, initially went with check valve that doesn't need to be replaced after use. The burst disk eliminates any possibility of backflow, but will need replacement if used.


Once the disc has burst, it cannot prevent backflow.
edit on 16-7-2019 by neutronflux because: Fixed



posted on Jul, 16 2019 @ 11:30 AM
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a reply to: nataylor

Why not use a valve?



posted on Jul, 16 2019 @ 11:35 AM
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originally posted by: nataylor

originally posted by: butcherguy
a reply to: firerescue
Replacing a check valve with a burst disk?
Something doesn't sound right about that answer.

What doesn't sound right? They both serve the same function. SpaceX, which is focused on reusability, initially went with check valve that doesn't need to be replaced after use. The burst disk eliminates any possibility of backflow, but will need replacement if used.

A check valve is repeatable, it serves to prevent backflow repeatedly. A check valve restricts flow to one direction.
A burst disk is used to vent excess pressure once the burst pressure is exceeded.
They do not serve the same function.
If a burst disk is adequate to do the job that they need, why would they have a check valve in the line?
edit on b000000312019-07-16T11:40:48-05:0011America/ChicagoTue, 16 Jul 2019 11:40:48 -05001100000019 by butcherguy because: (no reason given)



posted on Jul, 16 2019 @ 11:35 AM
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I wonder if it was manned in secret.. secret test subjects that would get rich after the test..



posted on Jul, 16 2019 @ 12:47 PM
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a reply to: nataylor



SpaceX, which is focused on reusability, initially went with check valve that doesn't need to be replaced after use. The burst disk eliminates any possibility of backflow, but will need replacement if used.


Problem is no matter how well designed or made, a mechanical device is subject to failure - proving Murphy correct

I am still wondering how the burst disc serves the same function in preventing back flow up the fuel lines, unless made a determination that one pressurized it doesn't matter



posted on Jul, 16 2019 @ 01:30 PM
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originally posted by: butcherguy
If a burst disk is adequate to do the job that they need, why would they have a check valve in the line?


More reusability. Check valves were used with the idea in mind that they could be reused on the next launch without being replaced. A burst disk requires replacement after each launch.

from the article:

Burst disks are single-use and inherently unreusable, but they are also completely passive and simply do not leak until subjected to a specific amount of pressure.


It was the act of the NTO "slug" ramming into the check valve and destroying the valve that caused the explosion. If the valve was a burst disc instead, the ramming NTO slug would cleanly burst through it rather than destroy the valve.


EDIT TO ADD:
I think people are confused about the "leaky component" being the check valve; I don't think it was. I think the leaky component caused the NTO slug, and that NTO slug then violently rammed into the check valve, which destroyed the valve and caused the explosion.

This excerpt from another article explains it a little better:

SpaceX said the most likely cause of the explosion was when a "leaking component" allowed nitrogen tetroxide (NTO) oxidizer into helium tubes during processing. When the system was pressurized just before the planned ignition, a "slug" of NTO was driven at high speed into a titanium check valve, causing structural failure of the valve and igniting it, triggering the explosion.

"When you pushed the slug [of NTO] into the check valve, it basically creates an explosion," said Hans Koenigsmann…


www.space.com...

edit on 7/16/2019 by Soylent Green Is People because: (no reason given)



posted on Jul, 16 2019 @ 01:42 PM
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originally posted by: firerescue
I am still wondering how the burst disc serves the same function in preventing back flow up the fuel lines, unless made a determination that one pressurized it doesn't matter


Bingo. This is for the abort motors. When they fire, the helium system pressurizes the propellant system, which then burns to depletion (both of the propellant and helium pressurant). There will be no propellant left to backflow.

The check valves were a convenience. SpaceX conducts a static fire test of the SuperDraco abort motors on each capsule. Now they will have to go in and change out the spent burst disks after that test. The check valves would have saved them that step.



posted on Jul, 16 2019 @ 02:07 PM
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originally posted by: Soylent Green Is People
EDIT TO ADD:
I think people are confused about the "leaky component" being the check valve; I don't think it was. I think the leaky component caused the NTO slug, and that NTO slug then violently rammed into the check valve, which destroyed the valve and caused the explosion.

This excerpt from another article explains it a little better:

SpaceX said the most likely cause of the explosion was when a "leaking component" allowed nitrogen tetroxide (NTO) oxidizer into helium tubes during processing. When the system was pressurized just before the planned ignition, a "slug" of NTO was driven at high speed into a titanium check valve, causing structural failure of the valve and igniting it, triggering the explosion.

"When you pushed the slug [of NTO] into the check valve, it basically creates an explosion," said Hans Koenigsmann…


www.space.com...


I would say the check valve is likely to be what caused the leak. But, because it was destroyed in the explosion, they can't say for sure. So they're limited to saying a non-specific component is the cause. But in the call, you tell they're assuming the check valve was the culprit.

spaceflightnow.com...

The check valves are designed with a spring to open and close as needed.

“The problem is that sometimes the spring is a little bit sticky,” Koenigsmann said. “The valve has moving parts, and so that’s why things sometimes, especially at low pressure, are not quite sealing as well as they’re supposed to in check valves.”



posted on Jul, 16 2019 @ 02:26 PM
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a reply to: nataylor

Thanks for the clarification!



posted on Jul, 16 2019 @ 11:37 PM
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a reply to: butcherguy
it has to do with the original design of the crew dragon. It was originally designed to be able to land in a propulsive fashion which would require the capacity to start stop and restart the super draco engines.

nasa said they don't want that capability, and only want it used for abort situations to save the crew.

due to this a check valve was left in place, and was originally passed as OK by both nasa and spacex as it had been used successfully multiple times before.

since it will only be used for emergency situations and firing one time, a burst disk can be used.

from what i have read about the situation there was a leak of oxidizer that got past the check valve and sat in the titanium portion of piping leading from the compressed helium tanks. As the helium tank was opened to begin the ignition sequence it shot the oxidizer through and compressed it against the titanium piping creating a reaction with the titanium near the check valve resulting in the check valve failing and further penetrating they oxidizer tank causing it to explode. when the oxidizer tank exploded it also destroyed the fuel tank. since it is a hypergolic set up this resulted in a big kaboom.

in the video of the explosion you can see this occur, as there is a non-flame explosion followed shortly by a fireball.

basically the oxidizer that leaked into the titanium portion of the piping acted like an airgun pellet, and the high pressure helium acted like the CO2 cannister. Except that since the helium was at something like 2400-3000 psi, and is light weight it pushes things through much much faster, and in this case it was the heavier oxidizer that leaked through the check valve.
edit on 16-7-2019 by dubiousatworst because: more autism

edit on 16-7-2019 by dubiousatworst because: (no reason given)



posted on Jul, 17 2019 @ 02:59 PM
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Summary - A complicated machine blowed up and the reason is (not surprisingly) a bit complicated.




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