SpaceX Falcon 9 historic landing thread (1st landing attempt & most recent missions)

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davdue said:
Just found this article on SpaceX.com: https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation
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TL;DR on the report is that a slug of nitrogen tetroxide (NTO) somehow got into the helium pressurization system. When that slug of liquid hit a check valve in the helium system, a titanium part within the valve broke off and caught fire (!) leading to the explosion. Purportedly, the SuperDraco thrusters recovered from the accident site "remained intact" after the explo ... anomaly. The check valves in question have been replaced with burst disks in future flight hardware.
 
What is interesting is that they finally used the word explosion. I don't think SpaceX has officially used that word yet.

Another note, it shows how much faith NASA has in SpaceX that they are moving forward before the end of the year with the abort test. That is a really quick turn around in the world of anomalys with NASA.
 
boatgeek said:
TL;DR on the report is that a slug of nitrogen tetroxide (NTO) somehow got into the helium pressurization system. When that slug of liquid hit a check valve in the helium system, a titanium part within the valve broke off and caught fire (!) leading to the explosion. Purportedly, the SuperDraco thrusters recovered from the accident site "remained intact" after the explo ... anomaly. The check valves in question have been replaced with burst disks in future flight hardware.
Click to expand...

I hate check valves.
 
Vital and trustworthy are independent variables.

I haven't met one yet that I couldn't backflow through. That's in 24 years of lab plant experience. Refinery unit ops.
 
The revised system will use burst disks to prevent that. If there's a need for abort, then those disks will be burst/busted.

Here's Scott Manley's take:

 
We had an interesting set of failures a while back on some. The check valves used were the type that seal off when you uncouple a fitting. This was part of a cooling system in a high power oscillator. We had a couple fail, with the plastic housings coming apart and dumping water where it wasn't wanted. Turned out that the spring in the fitting (the ends where the turns are together create a shorted turn) was getting excited by the RF and heating up, thus melting through the plastic parts :(.
 
OverTheTop said:
We had an interesting set of failures a while back on some. The check valves used were the type that seal off when you uncouple a fitting. This was part of a cooling system in a high power oscillator. We had a couple fail, with the plastic housings coming apart and dumping water where it wasn't wanted. Turned out that the spring in the fitting (the ends where the turns are together create a shorted turn) was getting excited by the RF and heating up, thus melting through the plastic parts :(.
Click to expand...

That's an awesomely obtuse failure mode!

The strangest one I've dealt with was less impactful - double sapphire beads in pump check valves. It turns out that if the dielectric constant of the material you're pumping is low enough, static charge from the fluid can't dissipate to the pump housing. Charge builds up on the beads and they start to levitate. Stop acting as a check valve. And thus stop pumping.

The SpaceX release doesn't actually say that the NTO leak was through the check valve that failed. I think Scott's video might be the core of the failure - but I think his picture is too simple. No one isolates fuel and oxidizer with single check valves. Of the coverage I've seen, only SpaceX itself seems to highlight what I think the big finding is: they discovered a new region of Ti flammability.
 
Charles_McG said:
The strangest one I've dealt with was less impactful - double sapphire beads in pump check valves. It turns out that if the dielectric constant of the material you're pumping is low enough, static charge from the fluid can't dissipate to the pump housing. Charge builds up on the beads and they start to levitate. Stop acting as a check valve. And thus stop pumping.
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I'll keep that one in mind for the future!

Charles_McG said:
The SpaceX release doesn't actually say that the NTO leak was through the check valve that failed. I think Scott's video might be the core of the failure - but I think his picture is too simple. No one isolates fuel and oxidizer with single check valves.
Click to expand...

I think the slug of NTO worked its way past the check valve when the system was at low pressure (no He pressurisation there) and a decent distance upstream. When the He was released the high pressure caused the NTO to hit the valve very fast, triggering the conflagration. It was about a cupful of NTO from what I heard. Not insignificant amount.
 
OverTheTop said:
I think the slug of NTO worked its way past the check valve when the system was at low pressure (no He pressurisation there) and a decent distance upstream. When the He was released the high pressure caused the NTO to hit the valve very fast, triggering the conflagration. It was about a cupful of NTO from what I heard. Not insignificant amount.
Click to expand...

From the SpaceX article:
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.
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They don't name the leaking component - but they do call out the helium check valve. That's why I think the leak was not at the check valve that failed, but elsewhere.

I certainly understand that a valve with a designed Cv expecting helium gas would go 'ping' with hit with thick, viscous NTO liquid at pressure. But a broken valve would just cause problems for re-use. And maybe cleanup after that particular test. SpaceX didn't anticipate the Ti being reactive with the NTO at all. The ping was the activation energy in a system they didn't anticipate being unstable in the first place.

So they can replace the checks with burst disks (of unspecified material - but I'm thinking not Ti :) ) because they've abandoned propulsive landings with the SuperDracos. If you only need to pressurize them once, you can make that kind of quick change.
 
Charles_McG wrote:
"I certainly understand that a valve with a designed Cv expecting helium gas would go 'ping' with hit with thick, viscous NTO liquid at pressure."
Click to expand...

My understanding is that the pressure was so great that the "ping" was more like a bullet. Not just a little energy, a LOT. I imagine say a high velocity 30.06 bullet going thru the pipe and hitting the valve. Lot of bad stuff gonna happen, including the release of the high-pressure helium past what may have been a shattered valve, as though it wasn't even there. And that's not even getting into the flammability of the Titanium in that situation.

I'm beginning to think of this as a SpaceX "Apollo-13" moment. A combination of design factors leading to a disaster that fortunately did not kill anyone.
 
In other Xspace news, the StarHopper caught fire after/during and engine test.

According to Musk the damage was minimal, so we'll see how things play out
 
Musk sez they'll try a "20 meter" hover test next week. This was after the post-firing fireballs in this week's static firing test delayed the hover test that was going to happen this week.

Musk is also sezzing they will land on the moon in 2021. Uhhhh....
 
georgegassaway said:
Musk sez they'll try a "20 meter" hover test next week. This was after the post-firing fireballs in this week's static firing test delayed the hover test that was going to happen this week.

Musk is also sezzing they will land on the moon in 2021. Uhhhh....
Click to expand...

You know the famous quote from Kelly Bundy....
 
Yep, today, unless it isn't.

John Kraus posted on Twitter (and the photo below):
"Falcon 9 and Dragon are poised to launch the CRS-18 mission to the International @Space_Station at 6:24pm EDT today, although poor weather conditions around Cape Canaveral are a concern. This is the second flight of this Falcon 9 booster, and third flight of this Dragon capsule!"

XF7d3Ch.jpg

If it's postponed, they'll try again Thursday.
 
Launch soon, at 6:24 PM EDT

NASA TV also has it.

UPDATE - Weather is reported as NO-GO, but they are waiting until the last minute to see if the weather improves.

UPDATE 2 - SCRUBBED. Rescheduled for Thursday at 6:01 PM EDT
 
Last edited:
Everyday Astronaut is on-site again with another live streaming of the Star Hopper 20 meter attempt. I am not sure if SpaceX will do another stream on this one, but they may so look out for it.

 
That's the Methane being vented and burned. Methane gas is denser than air (opposite of hydrogen/helium), so if not burned as it is vented, it will sink down to the ground, and can drift to some ignition point downwind and cause an explosion.
 

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