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

[DecoLV]

So this is my question too. In a ground static fire, the new burst discs would be, um, burst, wouldn't they? Consumed. Or are burst discs something closer to a valve that can be reset? If not they would have to be replaced for the IFA, right? Is that a big deal? Any kind of performance concern?

[Jcc]

They are not re-using the D2 for crew flights - Single crew flight only and then converted into cargo. A cargo D2 doesn't need refurbishment of the super dracos as it won't use them.

That information is already outdated. Cargo D2 do not have Super Dracos at all. Outer mold line reflects this as well. The idea to convert flown CCP Crew Dragons to cargo D2 is under review. SpaceX has come to the conclusion that it is likely more expensive to convert a flown Crew Dragon to cargo D2 than do an all-new build of cargo D2.

Does that mean crewed D2 capsules are about to be declared non-reusable?

They are non-reusable within the scope of CCtCAP. For the six missions now contracted with NASA the baseline is a new spacecraft for each of those six crew rotation missions.

Reuse of Crew Dragon on non-NASA missions is likely. BUT there are currently NO non-NASA missions for Crew Dragon on contract. And it is not likely any will surface. SpaceX wishes to move on to SS+SH.

However, cargo D2 is another matter. Expect reuse of those capsules fairly early into the CRS-2 program.

Jessica Jensen explained the situation quite clearly during a recent CRS press briefing.
 
--Crew Dragon is not currently certified for reuse, but SpaceX intends to work towards proving reuse and a contract modification to allow reuse, just like they did with Cargo Dragon-1.

--Cargo Dragon-2 is very different that Crew Dragon, it doesn't have Super Dracos, so used Crew capsules will never be used for Cargo, but they do intend to reuse Cargo Dragon-2.

[woods170]

So this is my question too. In a ground static fire, the new burst discs would be, um, burst, wouldn't they? Consumed. Or are burst discs something closer to a valve that can be reset? If not they would have to be replaced for the IFA, right? Is that a big deal? Any kind of performance concern?

Correct. In a ground static fire the burst discs will burst. After the ground static fire new burst disks will have to be installed, prior to the vehicle being used for the IFA test. The entire system must also be cleaned prior to IFA to remove any remaining burst disk fragments.

[Bananas_on_Mars]

So this is my question too. In a ground static fire, the new burst discs would be, um, burst, wouldn't they? Consumed. Or are burst discs something closer to a valve that can be reset? If not they would have to be replaced for the IFA, right? Is that a big deal? Any kind of performance concern?

Correct. In a ground static fire the burst discs will burst. After the ground static fire new burst disks will have to be installed, prior to the vehicle being used for the IFA test. The entire system must also be cleaned prior to IFA to remove any remaining burst disk fragments.

Just a little annotation, there are non-frangible burst discs/rupture discs available, so if they use those(not clear to me), they should not have debris of the burst discs inside their piping.

They also might use something called a reverse buckling rupture disc, because it's much stronger in one direction, which might be preferred in this case because the tanks might see many pressurization cycles on the other side for normal draco thruster use. Those have a dome that is pointed against the intended flow, once their design pressure is reached it buckles outwards and is sliced open by knife ore pin-like structures on the downstream side.

[Chris Bergin]

SpaceX’s Crew Dragon set for important test campaign

https://www.nasaspaceflight.com/2019/10/spacexs-crew-dragon-important-test-campaign/

By Michael Baylor.

https://twitter.com/NASASpaceflight/status/1187094417494159360

[FutureSpaceTourist]

https://twitter.com/thesheetztweetz/status/1187447486702673925

Scoop: SpaceX plans to static fire Crew Dragon's new SuperDraco system on Nov. 2 in Florida at LZ-1, people familiar tell me.

The test will be closely watched, as SpaceX looks to show it fixed the issue from the Demo-1 capsule explosion in April.

[FutureSpaceTourist]

https://twitter.com/jeff_foust/status/1189538775162073089

Latest update on the investigation into the static-fire anomaly that destroyed the Crew Dragon capsule in April. Static fire test with new Dragon now planned for next week; if successful, do in-flight abort test in early December.

twitter.com/chrisg_nsf/status/1189539189857181696

Kathy 3 things learned from #Dragon anomaly.
1. New pressure abort systems, good mass trade/capability.  But that led to low flow to high flow pressure wave wasn't realized.  We learned high pressure with exposed titanium that even NASA didn't realize was a thing.

https://twitter.com/chrisg_nsf/status/1189539463552262145

Put a durst disc in there to mitigate part of issue.  Even NASA had to make new compatibility matrix for this.  Knew there was migration, but didn't realize interaction.  SpX and NASA worked well together to make sure they all now understand this.

https://twitter.com/chrisg_nsf/status/1189539833754128384

Kathy doing a FANTASTIC job of detailing how NASA and SpX both didn't understand that there was an issue with this new system.  No one was to blame.  They tested and learned before it was an issue/"bad day" with a crew. #HEO #NAC

https://twitter.com/chrisg_nsf/status/1189539982505140224

Kathy: "Having this happen was a big wake up call for everyone and reminder of the risk and how we all have to be on top of things."  #HEO #NAC #Dragon.

[Comga]

Latest update on the investigation into the static-fire anomaly that destroyed the Crew Dragon capsule in April. Static fire test with new Dragon now planned for next week; if successful, do in-flight abort test in early December.

Kathy 3 things learned from #Dragon anomaly.
1. New pressure abort systems, good mass trade/capability.  But that led to low flow to high flow pressure wave wasn't realized.  We learned high pressure with exposed titanium that even NASA didn't realize was a thing.

Put a durst disc in there to mitigate part of issue.  Even NASA had to make new compatibility matrix for this.  Knew there was migration, but didn't realize interaction.  SpX and NASA worked well together to make sure they all now understand this.

Kathy doing a FANTASTIC job of detailing how NASA and SpX both didn't understand that there was an issue with this new system.  No one was to blame.  They tested and learned before it was an issue/"bad day" with a crew. #HEO #NAC

Kathy: "Having this happen was a big wake up call for everyone and reminder of the risk and how we all have to be on top of things."  #HEO #NAC #Dragon.

This brings up a fundamental question
While NASA (Bridenstine) is still saying there is 6 to 8 months of verification left, they are only reviewing parts and procedures against known criteria for understood risks.
This was not an understood risk.
The operation that triggered the explosion had been run many times.  The system did not fail in any of the previous tests.
If this capsule had not exploded during that test, this risk would have remained unknown, but serious.
The only way to find this was by full up testing.
No amount of pouring over data would have revealed it.
It could have remained unknown into the flight program.
That would say that getting flight data, from DM-1, the IFA, and DM-2, is more important than running years of reviews.
It is in SpaceX's interest to get to those tests without failure.
So are the extremely extended reviews by NASA adding to safety or degrading it by pushing off the tests that could reveal the "unknown unknows" for years?

[gongora]

That would say that getting flight data, from DM-1, the IFA, and DM-2, is more important than running years of reviews.
It is in SpaceX's interest to get to those tests without failure.
So are the extremely extended reviews by NASA adding to safety or degrading it by pushing off the tests that could reveal the "unknown unknows" for years?

The reviews and the test flights are both important.  Do you have some inside information that NASA is delaying the test flights (one of which is scheduled to fly in a little over a month) for "years" to push around unnecessary paperwork?  Do you have information that all of the systems on Dragon are ready for flight (despite public knowledge of parachute testing failures that led to a recent redesign of the parachute system, and recent changes to the propulsion system to address the test failure, and the DM-1 design having known problems that had to be fixed before flying crew)?

[Vettedrmr]

That would say that getting flight data, from DM-1, the IFA, and DM-2, is more important than running years of reviews.
It is in SpaceX's interest to get to those tests without failure.
So are the extremely extended reviews by NASA adding to safety or degrading it by pushing off the tests that could reveal the "unknown unknows" for years?

The reviews are months long, not years.  NASA's review process may seem extended to those not in the safety community (I was for about 8 years), but it is thorough.  If not for NASA's insistence on parachute drop tests, would we have learned what we did? 

It's difficult to ferret out the unknown unknowns.  Sometimes those happen during the review process.  That happens and you never hear about it.  Sometimes it gets past the review process and shows up in the test phase.  We never say that we want zero failures; what we want are zero fatal failures. 

So, while I want SpaceX and Boeing both to get crew-rated as soon as possible, that "possible" usually takes longer than we wish.

HTH, and have a good one,
Mike

[baldusi]

i think the question is one of tradeoffs: when a bit less analysis and more integrated testing would be cheaper/faster? And please note that this is organization dependent. An organization excellent at analysis but very slow/expensive at manufacturing, will probably do better with more analysis. An organization without much analysis experience but cheaper/faster manufacturing, would probably have to go with lots of actual testing.

[OTV Booster]

This brings up a fundamental question
While NASA (Bridenstine) is still saying there is 6 to 8 months of verification left, they are only reviewing parts and procedures against known criteria for understood risks.
This was not an understood risk.
The operation that triggered the explosion had been run many times.  The system did not fail in any of the previous tests.
If this capsule had not exploded during that test, this risk would have remained unknown, but serious.
The only way to find this was by full up testing.
No amount of pouring over data would have revealed it.
It could have remained unknown into the flight program.
That would say that getting flight data, from DM-1, the IFA, and DM-2, is more important than running years of reviews.
It is in SpaceX's interest to get to those tests without failure.
So are the extremely extended reviews by NASA adding to safety or degrading it by pushing off the tests that could reveal the "unknown unknows" for years?

This operation, firing the SD’s after firing the Draco’s, had never been done before. But you're right that no amount of analysis would have found it.

SX gives the illusion of slipshod because they do things so fast. They are anything but slipshod. They ran that test because it needed to be done.

[baldusi]

If I'm not mistaken, the problem was not Draco then Super Draco. It was that they had fired those SD before, and fuel had crept past the one way valves.

[mn]

....
SX gives the illusion of slipshod because they do things so fast. They are anything but slipshod. They ran that test because it needed to be done.

Your statement almost sounds like they knew there's a potential issue and ran this specific test to see what would happen.

If I understand your statement correctly, I'd argue that it is most certainly not true.

Unless you mean just in general that they are very thorough and therefore ran this test.

[whitelancer64]

i think the question is one of tradeoffs: when a bit less analysis and more integrated testing would be cheaper/faster? And please note that this is organization dependent. An organization excellent at analysis but very slow/expensive at manufacturing, will probably do better with more analysis. An organization without much analysis experience but cheaper/faster manufacturing, would probably have to go with lots of actual testing.

Tests don't mean ANYTHING unless you review the data and analyze it thoroughly to understand what you've found.

The formal reviews also ensure that everyone on both sides is on the same page. Reviews can also uncover previously unknown issues or deficiencies.

[ulm_atms]

I say the fact that NASA let the capsule touch the ISS, which means NASA, Roscosmos, and others all signed off without a mention/worry/concern of the issue that blew up DM-1 is a testament and a gold standard example of "Unknown, Unknowns"  This also shows that software modeling/testing is only as good as the input criteria and known knowns.  It helps prevent the easy but overlooked ones...not the WTH just happened ones.  That's why I don't like that they want to skip testing on the SLS (green run for example).

I will give SpaceX this.  Their pushing of the boundaries and trying different, not done before methods sure have yielded quite a few unknown, unknowns.  This and the solid O2 in COPVs are good ones.

[OTV Booster]

....
SX gives the illusion of slipshod because they do things so fast. They are anything but slipshod. They ran that test because it needed to be done.

Your statement almost sounds like they knew there's a potential issue and ran this specific test to see what would happen.

If I understand your statement correctly, I'd argue that it is most certainly not true.

Unless you mean just in general that they are very thorough and therefore ran this test.

I meant the latter.

[OTV Booster]

If I'm not mistaken, the problem was not Draco then Super Draco. It was that they had fired those SD before, and fuel had crept past the one way valves.

I haven’t been following this for the past few weeks and if what you say is true it’s a fairly new finding. Or I misunderstood.

[rsdavis9]

If I'm not mistaken, the problem was not Draco then Super Draco. It was that they had fired those SD before, and fuel had crept past the one way valves.

I haven’t been following this for the past few weeks and if what you say is true it’s a fairly new finding. Or I misunderstood.

My understanding from previous discussion is that because the draco(rcs) and super dracos have cross feed the previous firing of the dracos left some N2O4 in the lines(leaking check valve). When the super dracos were pressurized this caused effectively a "water hammer" when this propellant on the wrong side of the check valve slammed into it.

Do I have this right?

[envy887]

If I'm not mistaken, the problem was not Draco then Super Draco. It was that they had fired those SD before, and fuel had crept past the one way valves.

I haven’t been following this for the past few weeks and if what you say is true it’s a fairly new finding. Or I misunderstood.

My understanding from previous discussion is that because the draco(rcs) and super dracos have cross feed the previous firing of the dracos left some N2O4 in the lines(leaking check valve). When the super dracos were pressurized this caused effectively a "water hammer" when this propellant on the wrong side of the check valve slammed into it.

Do I have this right?

SpaceX said the leak occurred in ground handling, which would seem to preclude that is occurred during firing of the Dracos. However, pressing the system for the Dracos could conceivably push oxidizer past a leaking check valve in the SD pressurant line, so I wouldn't entirely rule it out as a possibility unless SpaceX provides a more definitive answer of what ground handling caused the leak.