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

[dglow]

Agree. When Bridenstine says "communication was not good" he really means 'optics were poor' and 'bad PR'.

As for why this was the case for SpaceX's anomaly yet not for Boeing's, the answer is simple: leaked video.

[Kabloona]

When Bridenstine says "communication was not good" he really means 'optics were poor' and 'bad PR'.

Thank you for deciphering the double-speak. IOW, "SpaceX made me/NASA look bad, and I'm upset that they didn't hold a press conference to try to minimize the political fallout from the accident."

Now I get it. Sometimes you wish bureaucrats would just come out and say what they mean.

[envy887]

Agree. When Bridenstine says "communication was not good" he really means 'optics were poor' and 'bad PR'.

As for why this was the case for SpaceX's anomaly yet not for Boeing's, the answer is simple: leaked video.

Ironically, the video seems to have leaked because SpaceX was sharing it with NASA. JB blaming SpaceX for not addressing it publicly appears to me to be sending exactly the wrong message about internal sharing.

[RonM]

Now I get it. Sometimes you wish bureaucrats would just come out and say what they mean.

Good Lord, that would be the end of civilisation. What would Sir Humphrey say?

[LouScheffer]

Short the finger pointing, I suppose this is a good thing, even if that first press conference is going to be a bunch of people with serious looks on their faces going,

"No, we don't yet know the root cause of the incident."

"No, we really don't know the proximate cause either."

"No, we don't know how much this is going to affect the schedule, if at all."

"No, I don't know why I'm standing here, except that we don't want the media to be frustrated, I guess."

One thing that they could say that would decrease media frustration is "Here is a public domain video of the anomaly".   The detailed answers will come later, and the media knows that, but this gives them something to put in their article that will be fascinating to their audience.  It also avoids any appearance of a coverup.

[ChrisWilson68]

Short the finger pointing, I suppose this is a good thing, even if that first press conference is going to be a bunch of people with serious looks on their faces going,

"No, we don't yet know the root cause of the incident."

"No, we really don't know the proximate cause either."

"No, we don't know how much this is going to affect the schedule, if at all."

"No, I don't know why I'm standing here, except that we don't want the media to be frustrated, I guess."

One thing that they could say that would decrease media frustration is "Here is a public domain video of the anomaly".   The detailed answers will come later, and the media knows that, but this gives them something to put in their article that will be fascinating to their audience.  It also avoids any appearance of a coverup.

SpaceX has a lot of powerful enemies that like to latch onto anything they can to sow unjustified fear, uncertainty, and doubt.  Releasing a video of a failure just gives ammunition to that kind of unfair treatment.  I can understand why SpaceX would not want to do that, particularly at a time when they didn't have the information themselves to authoritatively refute such attacks.

[Chris Bergin]

Per the upcoming event, SpaceX clearly stated it was not to be posted on social media, so those sites who did aren't very good at reading bold letters on an e-mail.

And that's all I'm saying on it per trimming a tweet posted on here and why I'm posting as some of you will have seen it and wondered why we'd remove it. Risk is someone posting a tweet that shouldn't have been made here from an external source risks some numpty tweeting "just read on NSF forum....." and then we look like the naughty site.

Once the event starts, then we'll be posting and passing on items of interest.

[Chris Bergin]

SpaceX release:



On Saturday, April 20, 2019 at 18:13 UTC, SpaceX conducted a series of static fire engine tests of the Crew Dragon In-Flight Abort test vehicle on a test stand at SpaceX’s Landing Zone 1, Cape Canaveral Air Force Station in Florida.

 

Crew Dragon’s design includes two distinct propulsion systems – a low-pressure bi-propellant propulsion system with sixteen Draco thrusters for on-orbit maneuvering, and a high-pressure bi-propellant propulsion system with eight SuperDraco thrusters for use only in the event of a launch escape. After the vehicle’s successful demonstration mission to and from the International Space Station in March 2019, SpaceX performed additional tests of the vehicle’s propulsion systems to ensure functionality and detect any system-level issues prior to a planned In-Flight Abort test.

 

The initial tests of twelve Draco thrusters on the vehicle completed successfully, but the initiation of the final test of eight SuperDraco thrusters resulted in destruction of the vehicle. In accordance with pre-established safety protocols, the test area was clear and the team monitored winds and other factors to ensure public health and safety.

 

Following the anomaly, SpaceX convened an Accident Investigation Team that included officials from the National Aeronautics and Space Administration (NASA), and observers from the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB), and began the systematic work on a comprehensive fault tree to determine probable cause. SpaceX also worked closely with the U.S. Air Force (USAF) to secure the test site, and collect and clean debris as part of the investigation. The site was operational prior to SpaceX’s Falcon Heavy launch of STP-2 and landing of two first stage side boosters at Landing Zones 1 and 2 on June 25, 2019.

 

Initial data reviews indicated that the anomaly 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 – 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.

 

In order to understand the exact scenario, and characterize the flammability of the check valve’s titanium internal components and NTO, as well as other material used within the system, the accident investigation team performed a series of tests at SpaceX’s rocket development facility in McGregor, Texas. Debris collected from the test site in Florida, which identified burning within the check valve, informed the tests in Texas. Additionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability.

 

It is worth noting that the reaction between titanium and NTO at high pressure was not expected. Titanium has been used safely over many decades and on many spacecraft from all around the world. Even so, the static fire test and anomaly provided a wealth of data. Lessons learned from the test – and others in our comprehensive test campaign – will lead to further improvements in the safety and reliability of SpaceX’s flight vehicles.

 

SpaceX has already initiated several actions, such as eliminating any flow path within the launch escape system for liquid propellant to enter the gaseous pressurization system. Instead of check valves, which typically allow liquid to flow in only one direction, burst disks, which seal completely until opened by high pressure, will mitigate the risk entirely. Thorough testing and analysis of these mitigations has already begun in close coordination with NASA, and will be completed well in advance of future flights.

 

With multiple Crew Dragon vehicles in various stages of production and testing, SpaceX has shifted the spacecraft assignments forward to stay on track for Commercial Crew Program flights. The Crew Dragon spacecraft originally assigned to SpaceX’s second demonstration mission to the International Space Station (Demo-2) will carry out the company’s In-Flight Abort test, and the spacecraft originally assigned to the first operational mission (Crew-1) will launch as part of Demo-2.

 

[Chris Bergin]

https://twitter.com/ChrisG_NSF/status/1150850616098525187

Rather than repeating a chain for 10 posts. Click on that and you'll have an updating stream of answers.

[mmeijeri]

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.

[jabe]

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?

[jeffkruse]

"Evidence shows that a leaking component allowed liquid oxidizer – nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing."

I don't understand, what was the leaking component? 

[dglow]

One of the check valves, as I read it.

[jeffkruse]

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.

[envy887]

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.

[jeffkruse]

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?

[mmeijeri]

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 think it means that the NTO first leaked through the check valve up into the pressurisation line, and when the line was pressurised it slammed back into the valve, igniting the metal on impact. Heating of NTO vapour due to compression may also have contributed to the ignition.

[envy887]

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?

The sentence before says that NTO went up the helium line slowly in ground processing. Then it says the NTO went down the line rapidly when they rapidly pressurized the system.

It would have been like a helium-driven hydraulic hammer hitting the check valve, blowing it apart and rapidly burning the freshly exposed titanium metal.

[dglow]

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' during testing)

[whitelancer64]

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.