SpaceX Return to Fight and what was the anomaly

[Grendal]

The top comment from the link has a great explanation about the solid oxygen and how it may have caused the explosion.

Sorry I can't seem to copy and paste anymore on my IPad after IOS update...

Here we go:

For people who aren't understanding the "solid oxygen" comment, here's a likely scenario where this occurs:

The helium COPVs are sitting inside the oxygen tank. The oxygen tank is then filled with subcooled oxygen that's very close to oxygen's freezing temperature. The helium tanks are immersed in and covered by this liquid oxygen. The helium tanks are then begun to be filled. When you fill the tanks, initially before too much pressure builds up, the helium will be expanding from the pressure lines into the pressure vessels. This will cause an associated temperature drop from adiabatic cooling. This could cause the surface of the vessel to drop below the freezing temperature of Oxygen. There will now be tiny frozen/solid Oxygen crystals that develop in between the aluminum tank and the carbon fiber wrapping of the COPV. As the vessel is then pressurized these crystals are strongly compressed as the COPV expands by a few centimeters as it pressurizes. When you strongly compress an oxidizer and a fuel source (carbon fiber) you can cause spontaneous combustion if the pressures are high enough. This causes tank and COPV rupture and then the runaway explosion of the vehicle.

Edit: Some people don't quite understand what COPV are, so here's a nice manufacturing video of how they're made:

The Carbon Fiber is an essential portion of the strength of the tanks.

Thanks to "ergzay" for his explanation. He was then asked:

Would the tank not warm up as it's pressurized?
Yes it would, but initially the tank is empty and is possibly at a lower pressure than the oxygen tank. Thus the first bit of helium that shoots in will be expanding rather than pressurizing. Additionally if the crystals are inside the carbon fiber lattice and are being pressurized this pressure would keep the oxygen in ice form. Unlike water, ices of other materials (like oxygen) are more dense than their liquids and thus squeezing the ice would help keep it frozen.

Edit: Two other thoughts. They're not going to fill it constantly as pressurizing up to 3000+ psi (i forget exactly what pressure they use) would cause too much heating into the oxygen. They will thus likely do it in steps and let the COPV tank cool before continuing the helium filling. Then additionally, the incoming helium pressurant lines are going to be at 3000+ psi or it wouldn't be able to pressurize the tank. This means that even after the tank is already somewhat pressurized the incoming gas will be expanding into the tank.

I personally don't know how accurate ergzay's explanation is, but he seems to know what he is commenting on.

So according to EM the most likely explanation for the anomaly is a bad interaction between the supercooled liquids and the materials of the COPV. Thanks again to reddit user ergzay for the more detailed explanation of what that could possibly be.

 

[Cosmacelf]

Bottom line, SpaceX's use of super cooled LOX, contrary to what the entire rest of the industry uses, could be at fault here (doesn't mean they can't make it work, but it means their tolerances for everything go way down).

 

[HVM]

Reddit thread is removed and comments deleted... so we will see

 

[Cosmacelf]

Really??? How interesting. I'm sure that won't have any impact on the conspiracy theories. No sir.

 

[Grendal]

Reddit thread is removed and comments deleted... so we will see

Maybe it was a closed meeting and the details were not supposed to be made public. Or maybe the information was pulled from L2 NASAspaceflight forum. That forum discusses inside information and the users agree that the subjects discussed are not to be shared.

Our moderator might be asked to remove this discussion.

 

[Doug_G]

If TMC were to receive a proper takedown notification, with appropriate justification, then yes it would be removed. Otherwise not.

 

[ecarfan]

It might have been formation of solid oxygen in the carbon over-wrap of one of the bottles in the upper stage tanks. If it was liquid it would have been squeezed out but under pressure it could have ignited with the carbon. This is the leading theory right now

By "solid" I assume that is the same as "frozen", basically. So frozen O2 in contact with the carbon fiber can ignite? I hope someone can explain that chemistry to me. (Edit: my apologies, I see that upthread @Grendal posted something by "ergzay" that attempts to explain the theory)

The other thing we discovered is that we can exactly replicate what happened on the launch pad if someone shoots the rocket. We don’t think that is likely this time around, but we are definitely going to have to take precautions against that in the future. We looked at who would want to blow up a SpaceX rocket. That turned out to be a long list. I think it is unlikely this time, but it is something we need to recognize as a real possibility in the future.”

I was always pretty sure that SpaceX was taking the possibility of sabotage seriously, and that confirms that indeed they were. Glad they are going to take percautions in the future.

 

[Grendal]

Space News has an excellent article breaking down the leaked NRO speech. I would reference it but I am on a weird device that makes a link difficult to do.

Edit - Thank you Ecarfan. Yes, that is the article. It really gets into the details.

 

[ecarfan]

Do you mean this article? SpaceX's Musk says sabotage unlikely cause of Sept. 1 explosion, but still a worry - SpaceNews.com

Quote from the article:
In comments leaked just hours after a Musk presentation Oct. 13 to the U.S. National Reconnaissance Office (NRO), Musk also said “a leading theory” for the Sept. 1 failure is the formation of solid oxygen on the carbon composite overwrapped pressure vessel (COPV) — the helium reservoir that is immersed in the liquid oxygen tank on the Falcon 9’s second stage.

“It might have been formation of solid oxygen in the carbon over-wrap of one of the [helium] bottles in the upper stage tanks,” according to an excerpt of Musk’s remarks. “If it was liquid, it would have been squeezed out. But under pressure it could have ignited with the carbon. This is the leading theory right now, but it is subject to confirmation.”
------------------------------------

 

[Watts 4 Me]

Do you guy think if sabotage was at play that they would tell us?

 

[Doug_G]

Yes.

And it isn't.

 

[HVM]

Do you mean this article? SpaceX's Musk says sabotage unlikely cause of Sept. 1 explosion, but still a worry - SpaceNews.com...

Reddit hearsay and anonymous-expert... blah

 

[thegruf]

Yes.

And it isn't.

or maybe not. The fallout would be so severe that it would damage the industry massively.
An alternate would be an unpublicised agreement between the parties the is commercially hugely in Spacex favour.

and agreed, no it isn't and if it was genuinely plausible they would be searching the area for the bullet, it would be a big area but far from impossible

 

[Model 3]

Do you guy think if sabotage was at play that they would tell us?

If they could not prove it without any doubt: No. But if they could - yes.

 

[Doug_G]

or maybe not. The fallout would be so severe that it would damage the industry massively.
An alternate would be an unpublicised agreement between the parties the is commercially hugely in Spacex favour.

and agreed, no it isn't and if it was genuinely plausible they would be searching the area for the bullet, it would be a big area but far from impossible

That's assuming the "local competition" did it. There are any number of other possibilities.

Still, it is highly improbable. SpaceX has figured out a likely cause, so that is a far more likely resolution.

 

[Nikxice]

That's assuming the "local competition" did it. There are any number of other possibilities.

Still, it is highly improbable. SpaceX has figured out a likely cause, so that is a far more likely resolution.

The whole topic of a bullet conspiracy theory certainly does seem like a far-fetched idea, but I also understand why every possibility has to be considered. The closest I can come to a plausible scenario would involve a lone wolf, not a competitor. There would be too many in the know and eventually information would leak.

There is no obvious connection here, but the bullet theory reminded me of this wacko incident in 2012.
Gunshots Damage Historic Saturn V Moon Rocket
I don't believe the perpetrator was ever caught.

 

[thegruf]

Elon let the conspiracy theory run though, mostly for fun I'm sure
but there was that report about a shadow and an unexplained flash from the roof of the ULA building followed by reports of a Spacex employee trying to gain access to their roof and being refused.

I think we all like the idea of subterfuge but the reality is likely more mundane; LOX freezing in the COPV wrap due to a change in the fuelling procedures.

But what if they found the bullet?

 

[VolkerP]

The frozen oxygen and carbon overwrap reaction sounds plausible to me. I wonder why this didn't blow up the first time since SpaceX started to use superchilled LOX. Was there a change in fueling procedure?

 

[Cosmacelf]

The frozen oxygen and carbon overwrap reaction sounds plausible to me. I wonder why this didn't blow up the first time since SpaceX started to use superchilled LOX. Was there a change in fueling procedure?

That's the suspicion.

 

[Grendal]

RTF news. A tweet from Jeff Foust of Space News:

Josh Brost, SpaceX: should have LC-39A activated for launches in less than a month, hopefully F9 launch from there later this year.