Investigating the SpaceX Rocket Explosion of September 1, 2016

[Greg Bernhardt]

At 500 or 1000 fps, too many frames to store? Probably reserved for the launch alone, not fueling and test fires.

This is Elon Musk we're talking about. Storage is cheap.

 

[Jonathan Scott]

I think that the initial flame could not have been that fast and intense without significant amounts of both fuel and LOX pre-mixed by a powerful ejection event. I think that if the helium pressure vessel (COPV) failed abruptly (perhaps due to stresses caused by buoyancy forces or thermal contraction) it could well have burst the LOX tank and at the same time partially burst the fuel tank. In such a case, I'm sure there would be many possible sources of ignition, so no separate explanation is required for that and this seems to require only a single point of failure.

 

[mfb]

It's water vapor - condensed out of the air by cryogenic liquids.

And what is it's role

It does not have a role - it just occurs due to the rocket operation, when air passes very cold surfaces the water vapor condenses and forms this mist.

Payload used hydrazine.

The satellite fell down later and made its own explosion.

 

[mheslep]

This is Elon Musk we're talking about. Storage is cheap.

The Falcon 9 and it's launch operations are cheap. Reduced cost is the most notable aspect of the Falcon 9 relative to other launch vehicles.

http://www.abelcine.com/store/Phantom-Flex-High-Speed-Digital-Camera/#tabs

Phantom camera line from $50,000 to $150,000 depending on specific model and features.

 

[.Scott]

I think that the initial flame could not have been that fast and intense without significant amounts of both fuel and LOX pre-mixed by a powerful ejection event. I think that if the helium pressure vessel (COPV) failed abruptly (perhaps due to stresses caused by buoyancy forces or thermal contraction) it could well have burst the LOX tank and at the same time partially burst the fuel tank. In such a case, I'm sure there would be many possible sources of ignition, so no separate explanation is required for that and this seems to require only a single point of failure.

As I make my way through 9/3 on the nasaspaceflight.com forum, there seems to be more and more support for this. Also, based on that discussion, there are not 2 separate tanks - there is a "common bulkhead" separating the LOX and fuel. So a COPV failure only require the rupture of a single wall.

There is also discussion of:
* COPV issues with both the 1st and 2nd stages in previous flights.
* Whether there was a preplanned hold event. It's important in determining how far along SpaceX was in filling the LOX tank. It may have been full during the anomaly, or it may have been less than half full.

 

[nikkkom]

I think that the initial flame could not have been that fast and intense without significant amounts of both fuel and LOX pre-mixed by a powerful ejection event. I think that if the helium pressure vessel (COPV) failed abruptly (perhaps due to stresses caused by buoyancy forces or thermal contraction) it could well have burst the LOX tank and at the same time partially burst the fuel tank. In such a case, I'm sure there would be many possible sources of ignition, so no separate explanation is required for that and this seems to require only a single point of failure.

COPVs in S2 are designed to withstand buoyancy forces during 1st stage burnout, which are some 4..5 times larger than on a stationary rocket. Not likely to fail because of that.

COPV failure should be visible in tank pressure telemetry. However, it is not known whether SpaceX in fact has that telemetry. It's also possible SpaceX is unwilling to disclose that it's a COPV failure again (I think this has low probability).

 

[mfb]

It's also possible SpaceX is unwilling to disclose that it's a COPV failure again (I think this has low probability).

"We don't understand what happened" is the absolute worst case for SpaceX and trust of the customers. If they know what happened they will share it.

 

[RonL]

As I mentioned in my first post about the light rays showing an X pattern that looked like a good identifier of the initial explosion, is it possible that a hammer like affect took place through the liquid and knocked out the base seams, allowing that large flood of liquid coming out of the base of the fireball ? To me it looked like thousands of gallons falling. I think a broken pump line would have looked more like a flame thrower.

 

[liometopum]

The explosion is not symmetrical.

Using the second frame of the explosion, I have the "x-marks-the-spot" overlapped with a circle drawn to show how far, approximately, the blast had proceeded. But notice that flame is present far below the blast circle, and that flame is in the rocket's vapors, and only in the those vapors. We don't see flame anywhere else, outside the blast circle, except downward and to the left.

That suggests that the rocket vapors had fuel in it prior to the explosion.

 

[Jonathan Scott]

We don't see flame anywhere else, outside the blast circle, except downward and to the left.

I think it's already been mentioned (perhaps in Scott Manley's summary) that those areas are probably just reflected light from the main flash.

 

[jim hardy]

those areas are probably just reflected light from the main flash.

I second that. Water droplets reflect and diffuse light. I once saw(from about fifty miles) a night shuttle takeoff go through a cloud. The whole cloud illuminated like a lamp globe.

 

[liometopum]

Ok. That is definitely a point!
In argument, there are no vapor clouds visible in that lower area marked by the oval; you can easily see between the rocket and tower, for example. That is a lot of lamp globe effect on what must be a sparse cloud, but certainly possible given the intensity of the light. I am getting partially convinced, as the arrow points to a reflection. That is a lot of reflection though, without shadow. In any case, here are the images for review.

 

[jim hardy]

That is a lot of reflection though, without shadow. In any case, here are the images for review.

Thanks !
Here's yours at 3X

Is that part of a vapor cloud ? I tend to suffer excess of imagination so won't assert either way.
Peculiar, if it is vapor it's on upwind side suggesting a spill of something cold enough to bring air below dewpoint, probably 80 degreesF in Florida this time of year. Oxygen isn't much denser than air, water vapor is lighter, but cold air falls and so does fog ... so your picture is er, could be consistent with a LOX leak.old jim

 

[jim hardy]

speaking of reflections

one frame only, the second one , 71.77 at RowVid

If an electronic artifact it's one several pixels big? (i set RowVid to1080 )
Reflection off lens internal surface ? Vapor puff ? Fragment exiting to rear ? Other mystery objects are black, this one appeared to reflect toward camera...(there's some hysterical UFO claims on Youtube's lunatic fringe sites)

old jim

 

[liometopum]

Thanks Jim. I am sold on the reflection argument, so trash one hypothesis, and time to make a new one.

 

[liometopum]

LOX.
Here are some videos of liquid oxygen fires, and they are striking!

 

[mheslep]

Ok. That is definitely a point!
In argument, there are no vapor clouds visible in that lower area marked by the oval...

Which means no *water* vapor, or no vapor that is visible. Also means no supercooled vapor of any kind, which would immediately form a condensed water cloud.

 

[liometopum]

Which means no *water* vapor, or no vapor that is visible. Also means no supercooled vapor of any kind, which would immediately form a condensed water cloud.

The areas above and below, to the left, have vapor clouds. This area of the rocket appears free of vapor clouds. I am not sure what to make of that. Is the column of light just light, or is it flame?

 

[liometopum]

Here is another observation from the video, http://rowvid.com/?v=_BgJEXQkjNQ
Explosion frame 1 (EF1) produces an X, that we have shown earlier, and is shown here again, as the image on the left. Explosion frame 2 (EF2), shown on the right, has a wider and brighter X, and it appears slightly higher. I marked out a pair of lines on EF2 showing the wider area it covers.

Interestingly, the center of the area marked by the intersection of the four lines on EF2 is higher up, and seems to be following the vertical pipe highlighted by the white oval.

 

[Dotini]

For clarification, was there conceivably an ignition source such as atmospheric electricity discharge, or could mere contact between leaking LOX and fuel in the vicinity of the loading ports spontaneously ignite?

 

[Jonathan Scott]

For clarification, was there conceivably an ignition source such as atmospheric electricity discharge, or could mere contact between leaking LOX and fuel in the vicinity of the loading ports spontaneously ignite?

LOX and fuel do not normally spontaneously ignite when mixed, but it takes very little energy to ignite many materials in the presence of gaseous pure oxygen.
If there were some form of abrupt mechanical failure such as a tank or bulkhead splitting, then this would be very likely to produce additional potential sources of ignition.

 

[liometopum]

I posted on the NASA forum and asked what was at points A and B, in the last image I posted.

A. Not a lot is there, but that is around the height of the LOX/RP-1 tanks common bulkhead.

B. That is the frame for the cradle that supports the top of the vehicle.

 

[jim hardy]

If there were some form of abrupt mechanical failure such as a tank or bulkhead splitting, then this would be very likely to produce additional potential sources of ignition.

It that's a single tank with a bulkhead there's quite a temperature gradient right there in the middle.
LOX on top.

It's bigger than i thought...

http://www.spacelaunchreport.com/f91s2.jpg
The "TEA - TEB pyrophoric ignitor fluid" burns on contact with air.

First stage is lit from a tank on the ground
second stage carries its own ignitor fluid in a tank I've not found yet.

http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf
The second stage tank for Falcon vehicles is a shorter version of the first stage tank and uses most of the same materials, construction, tooling and manufacturing techniques as the first stage tank. A single Merlin Vacuum (MVac) engine powers the second stage, using a fixed 165 :1 expansion nozzle. For added reliability of restart , the engine contains dual redundant triethylaluminum-triethylborane (TEA-TEB) pyrophoric igniters.

 

[Dotini]

My guess is that a leak developed outside the rocket, common to the LOX and kerosene delivery systems and their fill ports on the side of the rocket. Ignition took place by atmospheric electrical discharge, probably coronal discharge on the gantry as the next thunderstorm was to arrive shortly.

 

[Jonathan Scott]

My guess is that a leak developed outside the rocket, common to the LOX and kerosene delivery systems and their fill ports on the side off the rocket.

You can't have a "common" leak in two separate systems. That would be two leaks. And the fire started higher up than the umbilicals.

 

[Dotini]

You can't have a "common" leak in two separate systems. That would be two leaks. And the fire started higher up than the umbilicals.

The last time NASA had a mishap in filling a rocket was about 1960. Obviously Mr Musk's people have some learning to do in filling their rocket. I will stand by my guess until the investigation unfolds the true chain of events.

 

[liometopum]

is a well done presentation of the SpaceX Falcon 9 explosion.
The creator of this video, Philip E. Mason, does a nice job linking the sounds to the video and explosion.
Greg... Mason talks some about the oddity that SpaceX did not have its own cameras recording this.
Jonathon, is his idea about the same as yours?

jim, on another of his videos, he discusses the 'bugs' flying by, in an often humorous fashion.

 

[mheslep]

Nice work from Mason. I agree the audio he draws attention to prior to detonation may be related, that they sound like stress failures. I disagree that it is absolutely certain that 2nd stage tank failure was the initial cause of the accident because the fireball initiates in that vicinity. The fueling lines were also in that area, and fueling was ongoing. The first frame of explosion has those lines engulfed by flame as well.

On the other hand, the LOX kerosene shared tank wall failure is plausible, if not certain. This leads to a possible major problem for SpaceX. The CEO Shotwell has said the firm will continue the flight schedule with this vehicle design. Unless SpaceX knows for *certain* that they can rule out an underdesigned tank from Falcon 9 mass reduction efforts, that the problem lies elsewhere, then they have no business returning to flight and doing so indicates some kind of cultural, firm-wide ego problem.

 

[mfb]

On the positive side, they have a large payload margin on every planned flight. A redesign (if necessary) would take time, but the same missions could still fly. In the worst case, the first stage would have to be expendable, but even that should be rare (limited to GTO missions).

 

[mheslep]

I agree that mechanically SpaceX has a way forward, even in the worst case. Culturally, maybe not. If indeed Shotwell's post accident, moving-along-nothing-to-see-here comment is indicative of some kind of NASA Challenger like, https://shop.spacex.com/mens/t-shirts/mission-to-mars-t-shirt.html-now-fever in SpaceX then a redesign won't fix that.

 

[mfb]

We know that whatever caused the explosion is not a fundamental issue with every rocket. In the worst case, it is something that happens occasionally. Every rocket has things that go wrong occasionally. As discussed before, a 5% failure rate is typical for rocket launches. If they keep that rate (the worst case: if they don't manage to find the issue and if they do not improve anything), it means another rocket will blow up at some point, probably within 2-3 years given the high launch rate. Yes. But ultimately: so what? They won't get contracts for manned missions then, but for many unmanned missions a 1 in 20 risk is fine if the launch is cheap enough. Note that this is the worst case, I don't expect that to happen.

You make it sound like this specific lost rocket is the worst thing that ever happened. Hundreds of rockets failed in the history of spaceflight. It is something that happens, despite great care of every launch service to reduce the risk as much as possible.

 

[Jonathan Scott]

Jonathon, is his idea about the same as yours?

That was a very interesting analysis.

His idea is almost the same as mine. Both start with a helium pressure vessel failure, leading to a rupture of the LOX tank. His idea seems to be that the rupture was in the common bulkhead, allowing the LOX and fuel to mix internally before the explosion. I felt that the initial explosion seemed to be just outside the second stage (this side of it and towards the right hand side) because of the way it illuminated things and because the flame did not expand anywhere near as rapidly between the first and second frames, suggesting that the initial burning material had been ejected before it caught fire. My guess is therefore that there was a rupture in the outer skin of the second stage before the explosion started, and that it was in the vicinity of the common bulkhead, allowing a lot of LOX and a little fuel to escape at the same time. He reckons that the cloudiness on the left of the initial explosion is probably excess liquid oxygen, which would make a lot of sense.

I'd agree that it does sound from the metallic reverberation as if the "quiet bang" a few seconds beforehand was probably also at the rocket (especially given the absence of other similar sounds earlier) but I don't know about the squeaky noise just before that. I have certainly heard similar noises from metal parts giving way!

I had assumed that if a pressure vessel had failed or similar a few seconds before the explosion, around the "quiet bang", SpaceX would have had clear telemetry showing overpressure in the LOX tank and would have a pretty good idea of what had happened. I had therefore been very puzzled as to how a helium pressure vessel failure could eject enough LOX and fuel to cause the explosion in only a small fraction of a second. Certainly, if the pressure vessel failure was a few seconds earlier then it seems quite plausible that it could create a leak which would build up invisibly but rapidly to produce that explosion. I'm guessing that venting valves would have been open on the LOX tank and that if a pressure vessel failed in a less abrupt way, the excess pressure would create much faster venting but might not build up pressure initially. It might also produce a lot of heat around the venting valve. I wonder if there is a LOX vent in the vicinity of the initial explosion?

 

[.Scott]

I felt that the initial explosion seemed to be just outside the second stage (this side of it and towards the right hand side) because of the way it illuminated things and because the flame did not expand anywhere near as rapidly between the first and second frames, suggesting that the initial burning material had been ejected before it caught fire.

However, the ejected material was burning - even at the leading burst front. So it had to contain a fuel (aluminum or the RP). And because it exceeded the flame propagation velocity, it had to be ignited before being ejected. So the material needed to start burning at or in the rocket and be ejected as burning material. Because the material was ejected towards the camera - but somewhat to the right, the bright spot appear further to the right than the center of the original rocket skin break.
The fact that the rate of expansion slowed between frames 1 and 2 together with the lack of shooting "cinders", suggests that the initial burning material was mainly the rocket fuel, not the aluminum or other solid parts. Solid parts, even finely fragmented, would more likely push through the expanding LOX cloud - out-pacing it and then quickly "quenching" when reaching the atmosphere. None of that is seen in the brightest sections of the first few frames.

My guess is therefore that there was a rupture in the outer skin of the second stage before the explosion started, and that it was in the vicinity of the common bulkhead, allowing a lot of LOX and a little fuel to escape at the same time.

If the outer skin rupture before the common bulk head, it happened between frames 0 and 1. It seems more like to me that the initial breach was to the common bulkhead near the outer skin and combustion perhaps combined with existing over-pressure forces a breach in the skin.

I'd agree that it does sound from the metallic reverberation as if the "quiet bang" a few seconds beforehand was probably also at the rocket (especially given the absence of other similar sounds earlier) but I don't know about the squeaky noise just before that. I have certainly heard similar noises from metal parts giving way!

Since the camera was overlooking a junk yard, I wouldn't treat junk yard sounds as part of the incident. Besides, metal filled with pressurized liquid doesn't reverberate very loudly - not enough to carry 2+ miles.

I had assumed that if a pressure vessel had failed or similar a few seconds before the explosion, around the "quiet bang", SpaceX would have had clear telemetry showing overpressure in the LOX tank and would have a pretty good idea of what had happened. I had therefore been very puzzled as to how a helium pressure vessel failure could eject enough LOX and fuel to cause the explosion in only a small fraction of a second. Certainly, if the pressure vessel failure was a few seconds earlier then it seems quite plausible that it could create a leak which would build up invisibly but rapidly to produce that explosion. I'm guessing that venting valves would have been open on the LOX tank and that if a pressure vessel failed in a less abrupt way, the excess pressure would create much faster venting but might not build up pressure initially. It might also produce a lot of heat around the venting valve. I wonder if there is a LOX vent in the vicinity of the initial explosion?

In last years incident, a pressure build up was seen - leading SpaceX to believe that it was not the COPV itself but a strut supporting that vessel. That would have caused the COPV to break away and vent through its top - a slower process than simply bursting. In these cases, either the COPV fragments or the COPV itself become a missile. In the NASA spaceflight forum, there are conjectures about whether some of the early debris flying from the second state are some of these COPVs.

 

[HyperTechno]

As already posted on PF, and you have likely seen in the news, a SpaceX rocket exploded, September 1, 2016. Elon Musk is reaching out for help in finding out how it happened. http://www.csmonitor.com/Science/20...calls-on-public-government-in-explosion-probe

I took the video and placed it in this, to allow frame-by-frame examination:
http://rowvid.com/?v=_BgJEXQkjNQ
Just in case... you can set the speed, for example, at .25 by clicking that button. Use the < and > buttons to move one frame at a time.

You will see, that at 71.7 (seconds) all appears ok.
The next frame, at 71.74, only 4/100 of a second later, the explosion is well under way. That is part of the problem for them, as it happened so quickly.

I already have my idea of what might have happened, and sent it along to reports@spaceX.com, but I want to let everyone else look for themselves to see if they can deduce anything. Some of the smart people at PF might be able to see something that the SpaceX people have not noticed.

Have fun.

Well, I too watched this on YouTube. There was a kind of dot above the spacecraft a moment before it exploded. Those videos claimed that as a UFO. But I don't believe it. I think the reason is some sort of a system malfunction.
[emoji89]

 

[HyperTechno]

It looked like the fuel tank... I agree with Jim hardy

Me too!