"Anomaly" During Crew Dragon Abort Engine Static Test

Yazata Online
They are calling it an "anomaly", but 'explosion' is more like it. Reportedly the Crew Dragon capsule, which was the same one that delivered Little Earth to the Space Station, was "all but destroyed". Flames and smoke were seen from the test stand at Cape Canaveral.

The NSF engineering geeks have spoken to an eye-witness at Cape Canaveral who saw the "anomaly". He says that he didn't see any rocket fire coming from the abort engines before things went wrong, the thing just suddenly blew up. Reportedly the capsule was what space-geeks call a "complete RUD" (rapid unscheduled disassembly, aka 'explosion'), was reduced to fragments and is obviously history. What's more, the "anomaly" wouldn't have been survivable if humans were aboard. That's all going to get NASA's attention.

This is going to set the upcoming in-flight abort test back by months, and DM-2, the first manned flight of the Crew Dragon, tentatively planned for July, will be lucky to fly before the end of the year, if it flies then. Obviously a great deal depends on what the investigation reveals caused the 'anomaly' and what kind of work is necessary to alleviate the risk.



Significantly, the Boeing Starliner, the Crew Dragon's main competitor as a commercial crew vehicle, suffered a similar failure and has been delayed for more than a year.

So it's fortunate that NASA has contracted for more Soyuz flights, since that's gonna be their only access to space for another year or so.

Somebody on a tour bus at Cape Canaveral got this photo

[Image: D4ok7ThXsAEPQr3.jpg]

[Image: D4ok7ThXsAEPQr3.jpg]

Yazata Online
(Apr 21, 2019 07:51 AM)RainbowUnicorn Wrote: what type of rockets are they ?

Don't know the technical details. Liquid fueled, don't know if it's hypergolic. The fuel is stored in 'COPV's, composite overwrapped pressure vessels, and initial speculation is that this is what blew. SpaceX relies on them heavily and they have had trouble with them before. A Falcon 9 blew up on the pad in 2016 because of a COPV failure.

Here's a short 20 second video that's already leaked out of Cape Canaveral, showing yesterday's explosion. It obviously would have been deadly to any astronauts on board.


There are speculations going around that SpaceX might have to completely redesign these abort engines. Perhaps make them solid fueled to get rid of the need for the COPVs. That would mean that the engines would only be one-time use and couldn't be restarted. I think that SpaceX originally planned that these capsules would land propulsively using these engines, but NASA said 'no way' if the capsules were going to be flying NASA astronauts. So SpaceX went with parachute descent, but kept the more capable (but more dangerous?) engines.

This is what it was supposed to look like. (SpaceX photo of an earlier pad abort test.) (Except that in yesterday's test the Crew Dragon capsule was tied down to the pad.)

[Image: 1557862.jpg]

[Image: 1557862.jpg]

Yazata Online
A Russian(!) chemist is opining that the brown vapor cloud in the photo in the first post appears to indicate the presence of Nitrogen Tetroxide. N2O4 is colorless, but breaks down to 2(NO2) at ambient temperatures, which is brown. (It's what makes smog brown.) Nitrogen Tetroxide is the normal oxidizer used with various hypergolic fuels such as Dimethyl-Hydrazine, which is the fuel-oxidizer mixture used by the Russian space agency Roscosmos. (Which has seen some failures, so they know those brown plumes.) NASA uses a variant on the same mixture.

(A hypergolic fuel is one that spontaneously ignites on contact with its oxidizer without any need for further ignition. Harder to handle, more dangerous and less thrust than regular rocket fuel, but good for smaller engines that get turned off and on repeatedly. SpaceX uses small amounts of hypergolics as lighter-fluid igniters for its big rocket booster engines. It was failure of that igniter system that prevented the center core on the first Falcon Heavy flight from relighting for its landing burn.)

The general thrust of speculation for this Crew Dragon explosion still seems to be towards the theory that a pressure vessel ruptured, tearing the Dragon apart, causing the hypergolic fuel and oxidizer to come into contact producing an even more explosive ball of flame.

Edit: Another line of speculation centers on the fact that these Super Draco engines and their supporting systems (including the pressure vessels) have been tested many times without any problem. Now this one particular Dragon goes into space, splashes down in the Atlantic, and subsequently fails. So there's speculation that something associated with the last flight (seawater? heating and cooling in the space environment?) caused a rocket engine to burst, rupturing the otherwise innocent pressure vessels and triggering an explosion that way.

Bottom line: Nobody knows yet. But engineers will speculate and invent failure scenarios. The only thing that engineers love more than speculating is getting their hands on some hard data! that allow them to prune branches off their fault-trees and home in on what really happened.
Yazata Online
Engineering talk (don't know if that's all it is) about fuel tank pressurization and engine chamber pressures.

Unlike the Cargo Dragon which only has one kind of rocket engine (the little Draco maneuvering thrusters) ,The Crew Dragon has two: the Dracos for maneuvering and attitude control, and the much more powerful SuperDracos for pad and in-flight aborts (and originally, for propulsive landing).

These are both pressure-fed rocket engines. They don't have fuel and oxidizer pumps. Fuel and oxidizer are forced into the engines from pressurized storage tanks. The rocket engines host an internal combustion process where the fuel burns, creating the rocket thrust which is the point of the whole thing. So each rocket engine has a chamber-pressure that produces the thrust that comes out of the nozzle. That means that in order for fuel and oxidizer to flow into the engines, the pressure in the storage tanks has to be greater than the chamber pressure in the engines. With big rocket engines like the SuperDracos, that calls for very high pressures in the tanks. Hence the COPV dangers referred to above.

More engineering difficulties arise from the fact that the Dracos and SuperDracos are both being fed from the same tanks but have very different chamber pressures. There needs to be a way to provide lower pressure fuel and oxidizer flow to the Dracos and higher pressure flow to the SuperDracos. That calls for separate plumbing for each kind of engine with elaborate pressure regulators and backflow valves.

All of which could have gone bad and caused the Crew Dragon to blow up.
RainbowUnicorn Offline
(Apr 26, 2019 05:56 AM)Yazata Wrote: More engineering difficulties arise from the fact that the Dracos and SuperDracos are both being fed from the same tanks but have very different chamber pressures. There needs to be a way to provide lower pressure fuel and oxidizer flow to the Dracos and higher pressure flow to the SuperDracos. That calls for separate plumbing for each kind of engine with elaborate pressure regulators and backflow valves.

thanks for the info
luckily my brain was switched to the correct mode so i managed to upload your posts.

what is the failure rate of production variance in the dual pressure fuel splitters ?

does the housing of the outer shell provide direct pressure on to the external side of the fuel tanks ? (re-entry/cooling etc)

"backflow " off the pad directing back to limit engine pressure resulting in ignition of the tank via low pressure ?

i am searching previous memory for pre failure plums currently and i do have some mental notes coming up.
not knowing the engineering means i dont know if the plume is pre or post critical failure point

the twitter link has been removed

i should imagine the tolerance for error in production of those duel exit fuel splitter castings must be extremely small.

is it new science materials ?

i assume sensors would show if a harmonic cascade had been triggered from a sonic reflection off the pad from the engine thrust  to cause potential spontanious conbustion or even an electrical static charging of the material of the tanks or engines ... ?

im just musing hope it helps if anything.
Yazata Online
Somebody isn't happy about the video of the Crew Dragon explosion leaking out to twitter (where it's since been removed) and then to the conventional media.

A new employee memo went out at Cape Canaveral yesterday threatening employees with termination if they are caught leaking unauthorized imagery.

The Orlando Sentinel story says:

"Contractors employed under the Test and Operations Support Contract, which NASA awarded to aerospace company Jacobs for ground systems capabilities, flight hardware processing and launch operations, were notified Monday of the new rules in light of the SpaceX video. The internal memo confirms the video is authentic and the capsule did explode, a fact that neither NASA nor SpaceX have yet confirmed publicly... [The internal memo includes:] "As most of you are aware, SpaceX conducted a test fire of their crew capsule abort engines... Subsequently, video of the failed test -- which was not released by SpaceX or NASA -- appeared on the internet."


So far, both NASA and SpaceX have been very careful to say nothing about this failure. They are aware of an "anomaly", they are investigating, "this is why we test", blah, blah, blah.
Yazata Online
NASA and SpaceX had a press conference today to discuss the upcoming cargo flight to the Space Station. It was unusually full of reporters and they all wanted to ask questions about the Crew Dragon that blew up. SpaceX's Hans Koenigsmann patiently answered them and quite a bit of new information came out.

The test had just concluded firing the smaller Draco thrusters. Then about half a second before the SuperDracos were to fire, the "anomaly" occurred (the thing blew up). So it pretty clearly had something do do with the preparations to fire the SDs. (Apparently very rapid pressurization of the system to a higher pressure to suit the bigger engines.)

Koenigsmann doesn't think that the SuperDraco rockets themselves were at fault (they have been tested some 600 times and in this case hadn't even fired yet). And he doesn't seem to want to blame the COPVs (the pressure vessels). In fact some of the COPVs are scattered around the test area where the explosion threw them, still intact and still pressurized. That's creating some danger that's slowing investigators from examining the explosion scene until they are taken care of and rendered safe. Suspicion seems to be on the various lines and valves that carry the pressurized gasses. (I have some doubts about this part, but I'm not an engineer and don't have inside information. But we know from the NTO plume that at least one oxidizer tank must have ruptured. Even if not all of the pressure tanks blew, an explosion only takes one. But... that rupture may have been the result of something else going wrong. Things can cascade.)

Koenigsmann was careful to say that he's been on a lot of accident investigations and it always seems to be that what he first suspects went wrong doesn't turn out to be at fault in the end. So he wants to keep an open mind and not prejudice himself by prematurely locking into a particular theory. The Dragon capsule was highly instrumented, returning a lot of telemetry, and there were high-speed cameras recording everything. Eventually they will be collecting all the pieces scattered around. So they have a lot to work through.

He has no idea what kind of delays this will cause in the SpaceX Commercial Crew flights. It's much too soon to speculate. It all depends on what caused the explosion, and what kind of changes they have to make in the capsule or in their procedures.

The transcript of the questions and answers is here:

Yazata Online
The investigation of the Crew Dragon anomaly/explosion is concluding. Turns out that the rocket engines and the COPV pressure tanks weren't at fault. Instead it was an entirely unexpected failure mode (which is why all the testing is valuable) and should be easy to fix.

Here's the relevant text from the official report:

"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."

Apparently they hadn't anticipated nitrogen tetroxide reacting that way with titanium (and NTO wasn't even supposed to be in those lines) so the whole failure mode was a 'never saw that happen before' for everyone.

The good news is that it will be easy to fix and the Crew Dragons already under construction can be modified to eliminate this particular risk.


The engineers point out that impact reactivity between nitrogen tetroxide and titanium has been known since the 1960's at least. In this case pressurizing the lines with helium created the impact conditions that caused the titanium and N2O4 to ignite.

See the discussion of nitrogen tetroxide on page 9 here:


But the engineers are questioning whether the reaction would have been energetic enough to blow up the entire capsule. So the ignition of the titanium/N2O4 apparently triggered something else to blow as well, maybe hydrazine. Suggesting that the chain of events might be more complicated than the snippet above suggests.
C C Offline
(Jul 16, 2019 07:31 AM)Yazata Wrote: The investigation of the Crew Dragon anomaly/explosion is concluding. Turns out that the rocket engines and the COPV pressure tanks weren't at fault. Instead it was an entirely unexpected failure mode (which is why all the testing is valuable) and should be easy to fix.

That April explosion was such a buzzkill that I forgot July was the original month for a demonstration mission. At least there's five more months left in 2019, but timing it with circa the Moon landing's 50th anniversary remains kaput.

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