SpaceX says Crew Dragon capsule exploded due to exotic titanium fire

As someone on reddit pointed out:<p>&quot;The following metals have been found to be incompatible with nitrogen tetroxide and must not be used: Aluminum 2024, Zinc, Aluminum 7075, Silver, K-Monel, Titanium, Brass Cadmium, Bronze Hastelloy, Copper, EZ Flow 45 Braze.&quot;[0]<p>[0]: Materials Compatibility with Liquid Rocket Propellants, <a href="https:&#x2F;&#x2F;apps.dtic.mil&#x2F;dtic&#x2F;tr&#x2F;fulltext&#x2F;u2&#x2F;866010.pdf" rel="nofollow">https:&#x2F;&#x2F;apps.dtic.mil&#x2F;dtic&#x2F;tr&#x2F;fulltext&#x2F;u2&#x2F;866010.pdf</a>

&gt; To do this, helium is rapidly pushed through a check valve - designed with low-molecular-mass helium in mind - to physically pressurize the propellant systems. Unintentionally, the NTO that leaked &#x27;upstream&#x27; through that valve effectively was taken along for the ride with the high-pressure burst of helium. In essence, picture that you crash your car, only to discover that your nice, fluffy airbag has accidentally been replaced with a bag of sand, and you might be able to visualize the unintended forces Dragon’s check valve (the metaphorical airbag) was subjected to when a &quot;slug&quot; of dense oxidizer was rammed into it at high speed.<p>This paragraph really drove the point home for me. I was able to easily visualize the event.

Direct link to SpaceX press release: <a href="https:&#x2F;&#x2F;www.spacex.com&#x2F;news&#x2F;2019&#x2F;07&#x2F;15&#x2F;update-flight-abort-static-fire-anomaly-investigation" rel="nofollow">https:&#x2F;&#x2F;www.spacex.com&#x2F;news&#x2F;2019&#x2F;07&#x2F;15&#x2F;update-flight-abort-s...</a>

I&#x27;ve taken these from other commenters, but can someone rectify these apparently contradictory statements for me?<p>&quot;The following metals have been found to be incompatible with nitrogen tetroxide and must not be used: Aluminum 2024, Zinc, Aluminum 7075, Silver, K-Monel, Titanium, Brass Cadmium, Bronze Hastelloy, Copper, EZ Flow 45 Braze.&quot;[0]<p>&quot;Titanium is practically the only metal that can store NTO for long periods of time over a reasonably large temperature range.&quot; [1]<p>[0]: Materials Compatibility with Liquid Rocket Propellants, <a href="https:&#x2F;&#x2F;apps.dtic.mil&#x2F;dtic&#x2F;tr&#x2F;fulltext&#x2F;u2&#x2F;866010.pdf" rel="nofollow">https:&#x2F;&#x2F;apps.dtic.mil&#x2F;dtic&#x2F;tr&#x2F;fulltext&#x2F;u2&#x2F;866010.pdf</a><p>[1]: <a href="https:&#x2F;&#x2F;ntrs.nasa.gov&#x2F;archive&#x2F;nasa&#x2F;casi.ntrs.nasa.gov&#x2F;19720019028.pdf" rel="nofollow">https:&#x2F;&#x2F;ntrs.nasa.gov&#x2F;archive&#x2F;nasa&#x2F;casi.ntrs.nasa.gov&#x2F;197200...</a>

FTA: “...instead of a mechanical check valve (simple but still not 100% passive), the barrier between pressurant and oxidizer (as well as fuel, most likely) will be replaced with something known as a burst disk.”<p>A burst disk comes from a different concept than a check valve. With a check valve, one presumably desires a fluid flowing in one direction—in this case the pressurant for the oxidizer vessel—and no back flow. In the rocket engine industry this setup tends to be used to maintain cleanliness. A burst disk, however, embodies the same concept as a relief valve—it prevents the pressurization of a system above its rated capacity. I fail to see how replacing a check valve with a burst disk fixes the problem and maintains the same system capability.

Too bad &quot;Some Birds Don&#x27;t Fly&quot;[0] is so expensive these days; interesting read on the early days of misslecraft<p>[0] <a href="https:&#x2F;&#x2F;www.amazon.com&#x2F;Some-birds-dont-Gary-Paulsen&#x2F;dp&#x2F;B0006BU29W" rel="nofollow">https:&#x2F;&#x2F;www.amazon.com&#x2F;Some-birds-dont-Gary-Paulsen&#x2F;dp&#x2F;B0006...</a>

Ooh a titanium fire - that would be really cool to see. I wonder if it&#x27;s possible to make titanium thermite as easily as aluminum thermite?

Doesn&#x27;t their solution preclude restarting the engines? Maybe that was never intended.

Exotic Titanium Fire would make a great band name.

&quot;Rockets are tricky.&quot;

Based on what just happened, this is somewhat alarming:<p><i>For the time being, NASA has published a tentative target of mid-November 2019 for Crew Dragon’s first crewed launch to the International Space Station</i><p>I&#x27;d rather fly 1,000,000 miles in a Boeing 737 MAX than risk one ride in this contraption. It surely needs quite a bit more unmanned testing before it can honestly be considered to be &quot;man rated&quot;.<p>Of course, NASA has a long and sordid history of pushing spaceflight while playing down many potential catastrophic problems. The Shuttle problems prove that.<p>And there&#x27;s no need to belabor Musk&#x27;s shortcomings. As someone on HN recently quipped, in response to Musk&#x27;s claim of full driving autonomy by 2020: <i>Tesla has an advantage here in that they don&#x27;t feel the need for their autonomy to be particularly safe.</i>