6
$\begingroup$

The crew dragon experienced an anomaly yesterday during testing. It seems that there was some sort of unexpected event that resulted in damage to the crew dragon test article. This unconfirmed video of the anomaly doesn't show exactly what happened. What happened on this test? Did the anomaly happen before or after the dracos were fired. What was the cause? How will this effect the time line for the first crew flight?

$\endgroup$
6
$\begingroup$

It was a leak in one of the fuel tubes

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.

The leak was apparently caused by a reaction between the nitrogen tetroxide and the titanium that comprises the tubes

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.

Apparently the solution is to go back to burst discs

On a call with reporters, Hans Koenigsmann, SpaceX's vice president of mission assurance, emphasized that the problem was entirely within the pressurization system and not tied to any flaws in Crew Dragon's engines. He said the company will be replacing the valves with burst disks that seal more completely to mitigate the risk.

$\endgroup$
3
$\begingroup$

I just reviewed several of the articles discussing it. Looks like Ars Technica has the best technical article with the most facts. Here's a link:

https://arstechnica.com/science/2019/04/heres-what-we-know-and-what-we-dont-about-the-crew-dragon-accident/

Here's a quick summary:

During a series of engine tests of the SpaceX's Dragon spacecraft this past Saturday, the vehicle experienced what the company has called an "anomaly" Based on leaked video the company was counting down toward a firing of the Dragon's SuperDraco thruster when the vehicle exploded. SpaceX has not validated the video but is consistent with verbal accounts shared with Ars Technica.

  • Initial tests were successful this was a later test in the testing sequence.
  • Anomaly occurred within the final 10 seconds of countdown, and it not clear whether the engines had begun to fire.
  • Reports the test was highly instrumented and they have lots of data.
  • No one hurt.

Here's my personal conjecture....happened toward the end of the test sequence, so it was probably a stress case. In other words, variations in the variable that were unlikely but possible.

Hope this helps.

$\endgroup$
  • 2
    $\begingroup$ What does this mean "variations in the variable that were unlikely but possible" ? $\endgroup$ – Organic Marble Apr 22 at 18:10
  • 1
    $\begingroup$ When performing an acceptance test such as this, the customer (in this case NASA) want to confirm that if unusual things happen then the system is still safe. I'm not sure what they would be for this application, some possible examples. 1. Rocket fuel at a warmer than optimal temperature. 2. Backup system activated, perhaps a backup pump or valve? 3. Excessive condensation. Perhaps even all of these at the same time. What we do, where I work is a "Failure Mode & Effects Analysis" (FMEA) to determine likely causes of failures. Then test the outer edges. $\endgroup$ – Rob Rogers Apr 22 at 20:15
  • $\begingroup$ Per this morning's press conference the thrusters had not yet begun to fire. Not much else is known $\endgroup$ – Machavity May 2 at 16:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.