SpaceX’s Crew Dragon spacecraft static fire anomaly - THREAD 3

[whitelancer64]

LOX ignited by carbon fiber. Titanium ignited by NTO. Geesh, SpaceX can't catch a break, can they?

(actually, good on them for catching this 'break', and during testing)

On the plus side, these first-of-their-kind failures are advancing the state of the art of aerospace materials science.

[Mark McCombs]

One of the check valves, as I read it.

" A slug of this NTO was driven through a helium check valve at high speed "

I read it as the leak caused the NTO to be in the line and then get driven into the check valve.

The job of the check valve is to prevent NTO from back flowing up the pressurant line. That is the obvious answer for what leaked, and there is likely no other route for NTO to even get into the line.

So this sentence " A slug of this NTO was driven through a helium check valve at high speed " is just a repeat of the sentence before it?

I read that during ground processing the check valved leaked allowing NTO into the pressurant line.  Then, during pressurization, a slug of NTO when (back) through the check valve causing the valve to fail and ignition to ocuur.

[Lar]

Interesting that yet again (as with the COPV) a type of combustion that was not expected was discovered.

Agree with others that this is certainly advancing the state of the art in this area.

I am not sure how burst disks can take the place of check valves if there is a need for material flow in one direction.

[jabe]

Interesting that yet again (as with the COPV) a type of combustion that was not expected was discovered.

high pressure does interesting things it seems

[freddo411]

Interesting that yet again (as with the COPV) a type of combustion that was not expected was discovered.

There is a reason the best textbook on rocketry  is named "Ignition!"

[mmeijeri]

I wonder if this will lead to similar design modifications to Orion and CST-100.

[jeffkruse]

IDK, working with scuba compressors, He and O2, check valves were always a problem.  We never used O2 >40% with Ti.

[dglow]

Bully on SpaceX for holding this conference and providing the release above. In one swift move they've come quite clean, sharing an abundance of what they currently know and how they've learned it, despite the investigation only being 4/5 complete.

This is a welcome balm in light of the discussion upthread and our hand-wringing around the administrator's recent comments. If this is a reflection of Bridenstine's new 'communication policy' well good on him too.

[RoboGoofers]

kinda sounds like one of those camping fire pistons.  the titanium was the fuel instead of char cotton.

[1]

I think it could be rephrased as "the check valve leaked NTO into the helium line, then when the high pressure helium actually flowed through the line, it pushed the leaked NTO back into the valve, where it interacted with the valve in such a way as to ignite."

More or less.

That's how I read it. Fits with how replacing the valve with a burst disc solves both problems.

[envy887]

So, nothing to do with hypergolics specifically, the explosion wasn't caused by hydrazine getting into contact with the NTO as some had speculated. It was an oxidiser problem, something that could in principle have happened with most other oxidisers too.

but curious why it happened on this test and not others..what was the difference?

The others did not have a leaky check valve.

[cuddihy]

So I wonder if this means the burst disks will burst as a part of a nominal abort motor firing to pressurize the propellant?
Makes sense, should eliminate leaking entirely...just makes testing a bigger problem. You’d have to replace disks every time you fire the abort system. Not a problem when you’re using the abort system to abort—that’s the least of your worries.

But verification the abort motor system is good gets much trickier.

[whitelancer64]

So I wonder if this means the burst disks will burst as a part of a nominal abort motor firing to pressurize the propellant?
Makes sense, should eliminate leaking entirely...just makes testing a bigger problem. You’d have to replace disks every time you fire the abort system. Not a problem when you’re using the abort system to abort—that’s the least of your worries.

But verification the abort motor system is good gets much trickier.

It shouldn't be that tricky. Presumably these valves are behind an access panel. Open panel, replace disk, close panel.

[jeffkruse]

So I wonder if this means the burst disks will burst as a part of a nominal abort motor firing to pressurize the propellant?
Makes sense, should eliminate leaking entirely...just makes testing a bigger problem. You’d have to replace disks every time you fire the abort system. Not a problem when you’re using the abort system to abort—that’s the least of your worries.

But verification the abort motor system is good gets much trickier.

It shouldn't be that tricky. Presumably these valves are behind an access panel. Open panel, replace disk, close panel.

But if the burst disk can be replaced then the method in which the burst disk is installed can leak.

[joek]

Bully on SpaceX for holding this conference and providing the release above. In one swift move they've come quite clean, sharing an abundance of what they currently know and how they've learned it, despite the investigation only being 4/5 complete.

This is a welcome balm in light of the discussion upthread and our hand-wringing around the administrator's recent comments. If this is a reflection of Bridenstine's new 'communication policy' well good on him too.

Agree.  Very thankful for the additional communications and rapid change after Bridenstine's statement.  Would be interesting to know what changes were instituted as a result of that new policy.  If it is a new policy, there should be some guidance (paper trail).

Given the taxpayers and the press were named as having an issue with the old policy--and thus presumably beneficiaries of the new policy--would be reasonable to ask for details.  Specifically, what is the new policy-protocol-whatever?

[mlindner]

Bully on SpaceX for holding this conference and providing the release above. In one swift move they've come quite clean, sharing an abundance of what they currently know and how they've learned it, despite the investigation only being 4/5 complete.

This is a welcome balm in light of the discussion upthread and our hand-wringing around the administrator's recent comments. If this is a reflection of Bridenstine's new 'communication policy' well good on him too.

Bridenstine had no right to come out publicly and blame SpaceX behind their back for not releasing information just before they actually had the information. It's entirely foul play and not acknowledging it as that is disingenuous. That could have entirely gone directly to SpaceX requesting them to release information publicly. Shaming them in public is extremely counterproductive.

Bridenstine deserves no praise here. He deserves rebuke for what he did.

I praise SpaceX for resisting the urge to release early and Elon for not saying something off the wall in regards to this and waiting until proper information is available. SpaceX performed perfectly with regard to this.

NASA (Bridenstine) got egg on face with leaking an internal video and then chose to blame SpaceX instead of admitting their mistake

[JBF]

So, nothing to do with hypergolics specifically, the explosion wasn't caused by hydrazine getting into contact with the NTO as some had speculated. It was an oxidiser problem, something that could in principle have happened with most other oxidisers too.

but curious why it happened on this test and not others..what was the difference?

The others did not have a leaky check valve.

The way I read it the initial issue was in the ground side equipment.  So for this test different ground side equipment was  used.

[dglow]

So I wonder if this means the burst disks will burst as a part of a nominal abort motor firing to pressurize the propellant?
Makes sense, should eliminate leaking entirely...just makes testing a bigger problem. You’d have to replace disks every time you fire the abort system. Not a problem when you’re using the abort system to abort—that’s the least of your worries.

But verification the abort motor system is good gets much trickier.

Heh, this is only true because SpaceX have so thoroughly spoiled us to expect full and rapid reuse! By contrast, how many times do you think Lockheed can (re-)test Orion's abort system?

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.

[mlindner]

I wonder if this will lead to similar design modifications to Orion and CST-100.

It should, Titanium is used everywhere for NTO. The fact it can burn it I don't think is well known. Titanium is generally pretty non-reactive.

[jabe]

I wonder if this will lead to similar design modifications to Orion and CST-100.

It should, Titanium is used everywhere for NTO. The fact it can burn it I don't think is well known. Titanium is generally pretty non-reactive.

found this tweet and following tweet interesting
https://twitter.com/wikkit/status/1150855184924336128