SpaceX Investigating the SpaceX Rocket Explosion of September 1, 2016

[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!

 

[Jonathan Scott]

However, the ejected material was burning - even at the leading burst front...

I don't discount the possibility that the explosion started inside the stage, but I think it's more likely that material was ejected without being visible before it caught light (mostly oxygen with a much smaller amount of fuel) but that in the oxygen-rich environment the flame propagated extremely fast through it, immediately igniting much of the mixture. I also suspect that the apparent extent of the flames in the first couple of frames may be misleading, in that there is clearly such a bright light from the initial explosion that there is a lot of indirect light.

I'm aware of the junk yard; do we know if it was active in any way at the time? I've not heard of any other junk yard sounds being picked up.

Of course, if there were people anywhere near the camera, they would have seen the explosion before that sound was recorded, and could well have reacted in some way, causing the first sounds.

 

[jim hardy]

We don't know what a view from the other side would show.

Is this about where the camera was ? about 2½ miles SSE ?

 

[Jonathan Scott]

By using Google Earth 3D view and moving things around until the towers line up with the footage (matching the ratio of the spacing between the tops of the towers and also noting that the sphere to the right also matches in that case), then moving out for about 4km, I make it that the camera was further out to the west, around location 28.551189, -80.618837 which is about 4.2km from the site.

 

[jim hardy]

I think i like your location better than mine.
I hadn't noticed the power poles over there, had been looking for a spot with a high building . I only roughed in direction visually.

 

[.Scott]

I don't discount the possibility that the explosion started inside the stage, but I think it's more likely that material was ejected without being visible before it caught light (mostly oxygen with a much smaller amount of fuel) but that in the oxygen-rich environment the flame propagated extremely fast through it, immediately igniting much of the mixture. I also suspect that the apparent extent of the flames in the first couple of frames may be misleading, in that there is clearly such a bright light from the initial explosion that there is a lot of indirect light.

Reports are that the air was very moist - even accounting for the Florida locale. So any venting should have become immediately visible.

 

[mheslep]

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.

Falcon 9 failed catastrophically in 2 of the last 11 launches, and no there are not enough launches yet to say this series of 11 is the worst possible case. This could be the coin toss series that happens to show heads only twice in 11 flips. Atlas II launches by contrast were successful for all 63 attempts. The other Atlas models have similarly superior records. I'm not sure what point is to be made by reporting on the history of rocketry since it's inception, any more than one would judge acceptable passenger aviation by going back to the Wright Flyer, or since the era of the de Haviland Comet passenger jet when aircraft fell out of the sky once per week.

https://en.m.wikipedia.org/wiki/Atlas_II

Cheap launch costs may make failures tolerable to SpaceX, but it is no help to the payload customer who just had his satellite or resupply destroyed and his research or business time lost.

It may be the case that "great care" is always taken by SpaceX to "reduce the risk as much as possible " but I don't know that to be the case, and I think neither do you.

Again though, mistakes of the past are correctable with a reasonable acceptance of self evaluation. What might block change is a leadership imposed state of denial, which I see hints of in Shotwell's comment.

 

[.Scott]

By using Google Earth 3D view and moving things around until the towers line up with the footage (matching the ratio of the spacing between the tops of the towers and also noting that the sphere to the right also matches in that case), then moving out for about 4km, I make it that the camera was further out to the west, around location 28.551189, -80.618837 which is about 4.2km from the site.

I have it further to the east.
28.525209, -80.575614.

Here's how I'm spotting it:
1) Per Google map photo: There is one tower that is closest to the spherical tank. The towers are of triangular cross section, and the closest tower is pointing one vertex to the tank. The the distance between the tank and the closest tower is about 3.5 times the height of the tower triangle at ground level.
2) From the video: If we number the towers from left to right 1, 2, 3, then only tower 2 matches the criteria for the closest tower. This is further demonstrated by the way the towers are lit up by the explosions. Tower 3 is in the background. Tower 2 is in the foreground.
3) This makes things pretty easy. Tower 3 lines up with the center point between the tank and tower 2 - almost due south. Following that to a building about 2.5 miles away.

 

[mfb]

Falcon 9 failed catastrophically in 2 of the last 11 launches, and no there are not enough launches yet to say this series of 11 is the worst possible case. This could be the coin toss series that happens to show heads only twice in 11 flips.

If you want to cherry-pick, why don't you take just the last rocket and claim 100% loss rate? Starting the sequence directly at a loss introduces a huge bias. In addition, just a single launch failed. Amos-6 didn't get launched. For the next few launches, I expect that they will do the static fire test without payload.

Atlas limited to II and V is one of the few examples to be significantly below the 5% loss rate (1 partial failure in 128 launches). It is a very mature system, and you are cherry-picking again by taking the rocket type with the lowest loss rate. Why don't you include the previous Atlas rockets? Atlas E: 2 losses out of 23 lauches. Atlas H: 0 out of 5. Atlas G: 2 losses out of 6 launches. Atlas I: 3 losses out of 11 launches. All those were after 1980, the earlier versions were much worse. With Atlas II they finally got it working properly, 63 lauches without a loss.
7 losses in 45 launches for the early Atlas rockets. That's the number of launches they needed to fix all the various issues with the rocket. SpaceX is not at 45 launches yet and has a lower failure rate already.

I'm not sure what point is to be made by reporting on the history of rocketry since it's inception

I don't do that, the 5% are the current rate.

Cheap launch costs may make failures tolerable to SpaceX, but it is no help to the payload customer who just had his satellite or resupply destroyed and his research or business time lost.

It is. They have insurances taking this into account, and rocket plus insurance is still cheaper than other rockets. SpaceX gets so many launch contracts for a good reason.

It may be the case that "great care" is always taken by SpaceX to "reduce the risk as much as possible " but I don't know that to be the case, and I think neither do you.

You'll never launch a rocket if you don't do that.Edit:

And because it exceeded the flame propagation velocity, it had to be ignited before being ejected.

Apparent flame propagation velocity can also go up if the material is moving.

 

[Jonathan Scott]

Reports are that the air was very moist - even accounting for the Florida locale. So any venting should have become immediately visible.

I must admit that if the venting would need to have started several frames before the explosion, that would have been visible. I had initially been assuming an abrupt rupture of the tank followed immediately On the other hand, there is already quite a bit of venting visible, and it might not be easy to see venting in the general direction of the camera, only to the sides. So I'm definitely considering the alternative that it did start with a small actual explosion inside the second stage.

 

[Jonathan Scott]

I have it further to the east.
28.525209, -80.575614.

Here's how I'm spotting it:
1) Per Google map photo: There is one tower that is closest to the spherical tank. The towers are of triangular cross section, and the closest tower is pointing one vertex to the tank. The the distance between the tank and the closest tower is about 3.5 times the height of the tower triangle at ground level.
2) From the video: If we number the towers from left to right 1, 2, 3, then only tower 2 matches the criteria for the closest tower. This is further demonstrated by the way the towers are lit up by the explosions. Tower 3 is in the background. Tower 2 is in the foreground.
3) This makes things pretty easy. Tower 3 lines up with the center point between the tank and tower 2 - almost due south. Following that to a building about 2.5 miles away.

Look at the direction of the steps or whatever they are on the spherical tank. They are clearly on the right of it, not on the front of it, from the viewpoint. They could of course have moved them, but there are other clues such as the buildings on the left which exactly match the view from the west, including for example the sloping roof whose ridge line is under the middle of the leftmost tower.

 

[Dr. Courtney]

Doing frame by frame, this is what I see:

50 to 71.73: Nothing of any significance.

71.77: In 40 msec or less, the "explosion" is already 17 feet high and wide. This is excluding illuminated sections of the booster that, on first glance, might appear to be part of the fire. Presuming that we started with a point source of ignition, this means that the illumination border has been moving at 8.5 feet in no more than 40msec or >210 feet per second or more.

71.81: In the next 40msec, the flames have continued to expand laterally, but the bottom of the flame has actually shortened! Moreover, a "cloud" created from cold temperatures along the bottom half of the booster is left undisturbed during this time - and for at least 10 frames that follow.

So at first, it would seem that what we are seeing in these first two frames is purely a flame propagation front. It would seem that an invisible and combustible mixture of gases was already there, hanging as a cloud in the air, when it became ignited.

But there's a problem. Flame propagation rates are measured in cm/sec, with our 210 feet per second being over 5300 cm/sec. Among the fastest propagation rates in air is a 38% mixture of hydrogen which tops out at roughly 480 cm/sec (http://www.comtherm.co.uk/CT-7a%20Fig.pdf). So, unsurprisingly, we are definitely working with something more potent than air.
Perhaps the chemists among us can come up with a mixture that will propagate at 6400 cm/sec. For comparison, the source above rates methane/air at about 70 cm/sec while this http://www.sciencedirect.com/science/article/pii/S0360544212005579 shows a oxy-methane mixture at about 295 cm/sec. Even assuming that hydrogen gets the same boost (haven't found a source on that), it would still fall short of our 6400 cm/sec. Besides, our gases should be on the cold side - slowing the burn rate down a bit.
So did something, perhaps turbulence or heat, enhanced the flame speed? Or perhaps the flame spread without incandescing for a few frames before becoming visible?

The flame propagation theory seems to have a problem.

Alternatively, both the the material that is burning and the oxidant could be ejecting laterally from the tank - carrying the flame with it. From what I can tell, this is exactly what is happening. The combustion started within the tank, created a lateral crack in the wall, and sprayed out.

I've worked a bit with high speed video of deflagration to detonation transitions in oxy-fuel mixtures. Summary: a wide variety of velocities are possible between the deflagration velocities one might look up in a source and the detonation velocities. Things can "sputter" like they are approaching detonation, but then slow back down. Lots of environmental factors change DDT transition issues and whether a reaction gets to detonation. A lot of this field is more art than science, and if all you have is a bound on the flame velocity, you can't say much. I do agree that a higher concentration of oxygen than found in air was most likely involved.

You know better than me, but c'mon, this is space age stuff and Elon Musk. I've seen spy satellite footage better than what I've seen. In this thread are we just seeing footage from visitors watching?

Agreed. There should have been better and more systematic monitoring of the system including high speed cameras with much better frame rates and resolution. Some nearby blast pressure sensors (sampled at 10 MHz) in the near field and some pzt based microphones in the far field sampled at 100 kHz would be valuable also. It is well known that a significant percentage of launches fail. There should have been due diligence to collect the event data for diagnosing the hows and whys when it happens.

 

[.Scott]

Apparent flame propagation velocity can also go up if the material is moving.

Exactly.

 

[jim hardy]

I have it further to the east.
28.525209, -80.575614.

i'm not in same league as you guys with imagery...
Using Google Maps' "measure distance" i am able to put a straight line from launchpad to proposed camera sites without losing resolution.
That's how i came up with my spot
which is halfway between .Scott's and Johnathan Scott's
so i feel successful !

i was looking for that distinctive three phase power pole

but there's a ring of them around the complex and it looks like it's nearer the camera than that.

 

[.Scott]

Look at the direction of the steps or whatever they are on the spherical tank. They are clearly on the right of it, not on the front of it, from the viewpoint. They could of course have moved them, but there are other clues such as the buildings on the left which exactly match the view from the west, including for example the sloping roof whose ridge line is under the middle of the leftmost tower.

I've tried to do some finer measurements. I can't nail it, but I have convinced myself that it is further west than I thought.

 

[liometopum]

The software used by Philip E. Mason to make his "Detailed analysis of Spacex Rocket Explosion" video was Sony Vegas Pro. I downloaded it.

To get a copy of the YouTube video to insert into Vegas Pro, this site was great: http://en.savefrom.net/1-how-to-download-youtube-video/
I placed the ss in front of the address, as recommended, and got a copy that worked perfectly.

You can play the video and listen clearly to the sounds.

The squeak and pop are further support, to me, that the whole thing started on the surface of the rocket. I don't think that the squeak and pop could have come from inside the rocket.