Investigating the SpaceX Rocket Explosion of September 1, 2016

[GeorgeDishman]

The videos above are available in 1080p60 but the default is much lower.

 

[Greg Bernhardt]

The videos above are available in 1080p60 but the default is much lower.

Still very weak when we're talking Elon Musk level.

 

[mfb]

What I want to know is why there aren't super high res cameras covering the launch pad? All I've seen is grainy photos and video.

Maybe they have that. Who knows?

Cameras tend to be far away to survive the rocket firing, so getting a good resolution is challenging.

 

[Greg Bernhardt]

Cameras tend to be far away to survive the rocket firing, so getting a good resolution is challenging.

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?

 

[jim hardy]

m, that is not a piece flying away. Go to 71.94 and look at the point at the bottom left hand corner, and then click until about 72.54. You will see the point go to the top right corner. I think that is a jet taking off from a nearby airport.

Good Eye !

I missed that.

 

[jim hardy]

On that sort of time scale? I think it's a bug flying past the camera.

at highest resolution there's several of them, some appearing for only one frame.
makes one wonder if this camera's sensor makes a true instantaneous capture or if the pixels are scanned sequentially, like old fashioned kinescope

If:
these are something real not an electronic artifact, and they're the same thing,
it was behind the fireball for two scans
are they some really fast moving things , or 'bad pixels' ?

 

[RonL]

I did see a couple of what appeared to be bugs, but everything else that wasn't shrapnel, I tend to think was bird movements, especially after things settled down a bit.

 

[mfb]

it was behind the fireball for two scans

You don't see small dark objects in front of very bright objects well with a camera.

 

[.Scott]

I think it's interesting that although the initial flash of flame and smoke expands rapidly, the expansion is in a sideways direction and the rate of expansion seems to be rapidly decelerating.

As I said in a previous post, I believe this is due to the fire starting in a contain space (the interior of the rocket) and bursting out. It's the only explanation I can see for the flames propagating in those first couple of frames much faster that a flame propagation front. Burning material - a fuel and oxidizer mix - must have been ejected through the side of the rocket, bursting along a horizontal seam.

 

[Jonathan Scott]

As I said in a previous post, I believe this is due to the fire starting in a contain space (the interior of the rocket) and bursting out. It's the only explanation I can see for the flames propagating in those first couple of frames much faster that a flame propagation front. Burning material - a fuel and oxidizer mix - must have been ejected through the side of the rocket, bursting along a horizontal seam.

I don't think that idea works, because the fuel and oxidiser are in separate tanks which are kept apart by a barrier which goes right across the 2nd stage, so it would not be possible for a significant amount to get mixed inside, especially together with a source of flame, unless something else had already gone wrong first.
I think that the second stage must have burst open just BEFORE any fire started, in a way which released both fuel and oxidiser, which subsequently caught fire. The only energy source I think could cause a sudden rupture that bad is that the helium pressure vessel inside the tank failed abruptly. I do not think a failure in either the oxidiser or fuel containment would have been able to create a large amount of mixed fuel and oxidiser so rapidly.

 

[mfb]

What would be wrong with a small explosion inside the rocket, quickly bursting the hull (which is not designed to handle significant pressure) for a fast initial expansion?

 

[Jonathan Scott]

What would be wrong with a small explosion inside the rocket, quickly bursting the hull (which is not designed to handle significant pressure) for a fast initial expansion?

I think you'd need quite a significant explosion inside the 2nd stage to push out enough oxidiser and fuel in a short enough time. Neither oxidiser nor fuel on its own will release chemical energy. Even if the LOX were heated locally by an electrical short (as in Apollo 13) I don't believe the expanding gas would have enough energy to cause that much damage that quickly. As I said before, there is a helium pressure vessel in the LOX tank which contains a lot of mechanical energy which could easily destroy the stage in a fraction of a second if it failed, so I think that's the most likely scenario.

 

[Jonathan Scott]

Given that there was a previous failure related to the helium pressure vessel, I might speculate that now that they have ensured that the support struts are strong enough, there might also be a problem with the way in which the supports, valves or other attachments are fixed to the tank, such that forces due to mechanical contraction or buoyancy during oxidiser loading caused the pressure vessel to rupture.

 

[jim hardy]

What single failures would release both fuel and oxidizer( or the ignitor fluid ) at the same time ?

Unrelated - is there a link to a "sequence of events " printout from telemetry ?

 

[nikkkom]

Dedicated spaceflight forum has some 56 pages of discussions already:

http://forum.nasaspaceflight.com/index.php?topic=30981.0

 

[jamalkoiyess]

What is this mist that get out of the top and the bottom at the very beginning and till the explosion? Is that liquid nitrogen ? And what is it used for ?

 

[.Scott]

What single failures would release both fuel and oxidizer( or the ignitor fluid ) at the same time ?

Unrelated - is there a link to a "sequence of events " printout from telemetry ?

The LOX burning through the metal until it reaches the RP. Maybe something that catalyzed the metal oxidation? Maybe something that heated up a spot on the metal? Maybe a material on the surface of the LOX tank that became exposed to high O2 gas concentration?

... or there was a fault in the Flight Termination System?

 

[.Scott]

What is this mist that get out of the top and the bottom at the very beginning and till the explosion? Is that liquid nitrogen ? And what is it used for ?

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

 

[.Scott]

Dedicated spaceflight forum has some 56 pages of discussions already:

http://forum.nasaspaceflight.com/index.php?topic=30981.0

Excellent forum. Here is a graphic from reply #751 in that thread.

The point is that the initial "explosion" seems to be aligned with the "common bulkhead", the divider between the 2nd stage LOX and RP tanks.
Several posters in that thread have cited the very energetic blast seen in the first couple of frames as evidence that the source must have been from within the rocket. Although none have specifically mentioned the frame propagation issue.

 

[liometopum]

Here is an X drawn on the first frame of the explosion to match the X of light produced:
ll

 

[liometopum]

Here is where the X is located on the rocket before the explosion (the last frame before explosion). Using the X of light places the point slightly higher than in the image .Scott posted.

 

[jamalkoiyess]

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

And what is it's role

 

[jamalkoiyess]

Does anyone have any information about the distance between the camera and the rocket and how much time did the sound take to arrive ?

 

[GeorgeDishman]

The point is that the initial "explosion" seems to be aligned with the "common bulkhead",

Why is everyone assuming the cause was in the rocket? The crosses marked also coincide with the bottom of the dark pipe between the main gantry and the outer casing which is clearly venting something. This image is the last before the explosion. If that vented material was coming from the gantry and detonated, blowing a hole in the side of the craft (it is designed for internal pressure, not external), then who is responsible for the gantry and launch facility?

 

[nikkkom]

Why is everyone assuming the cause was in the rocket?

"Everyone" is not assuming that. In fact, to me it looks like less than half of the theories put forward so far are "blaming" the rocket.

If that vented material was coming from the gantry and detonated, blowing a hole in the side of the craft (it is designed for internal pressure, not external), then who is responsible for the gantry and launch facility?

F9 doesn't have any cryogenic or volatile fuels onboard. It uses RP-1 (a refined grade of kerosene). The visible white venting should be cold oxygen (likely boil-off from LOX tank).
As to "who is responsible for the gantry and launch facility": SpaceX operates its own pad. It does not subcontract launch ops.

 

[liometopum]

Here is my hypothesis.

What we (think) we know:
1. The explosion appears centered on the connection between the rocket and the pipe. The explosion was external to the rocket.
2,. They were fueling the F9 at the time of the explosion.
So... is that pipe the place where the fuel is was being added?

Also observable:
3. The wind is blowing from right to left, as shown by the clouds of gas emitted by the F9.
4. Most rocket explosions look different, as they start slower. This started in an instant, less than 4/100 of a second, without any prior visible indication.

5. The first explosion frame shows fireballs far down the rocket, beneath the point of explosion..
6. Those fireballs are on the left side, in the vapor clouds.

7. The ignited gas, at these lowest levels of initial flash burn, have a story to tell.
7a..Looking at the first few explosion frames shows that these fireballs are separated, somewhat.
7b. The vapor burn is within the pre-existing clouds of vapor.
7c. The vapor burn areas follow the contour of the vapor clouds, That is, where the clouds are farthest to the left, so is the flash fire.
7d. There is no flashing or burning outside the vapor clouds.
7e. That means the volatile gases were already there, in the vapor; they were not pushed there from the point of the initial explosion.
7f. Even the vapor cloud directly to the left of the point of explosion flashes.
7g. The lowest areas of vapor clouds do not ignite. That probably helps us time when the fuel began leaking.

Hypothesis:
There was a leak in the 'fuel line to rocket' connection, Fuel was escaping for some time, prior to the explosion. Being heavier than air, the fuel vapors sank, and were carried to the left by the wind. The wind speed was variable, causing a contour of vapor to the left, and below, the point of emission of the fuel vapor (which was mixed with the other emission gases). Somewhere down lower, below the point of leakage, static electricity, or rubbing between parts, caused a spark, and that ignited the volatile gas which flash-burned outwards in all the directions it could. The flash went out to the furthest point in the vapor clouds containing fuel, and burned up to the point of leakage. There, at the leak, it ignited the fuel where it was leaking directly from the 'fuel line to rocket' connection and, due to high density of fuel there, burned hotter and faster and produced the explosion.

 

[.Scott]

Does anyone have any information about the distance between the camera and the rocket and how much time did the sound take to arrive ?

Just over 4000 meters. An audio delay of 12.1 seconds.

 

[Jonathan Scott]

2,. They were fueling the F9 at the time of the explosion.
So... is that pipe the place where the fuel is was being added?

They had completed fueling (with RP-1) earlier. They were loading LOX at the time (70% full). The pipes for loading LOX and RP-1 connect much lower down than the point of the explosion. As far as I know, there is no connection between the tower and the rocket at the point of explosion.

The rate at which the initial flame propagated seems too fast to be for a mixture of fuel and air. It suggests that LOX was involved, although at the left hand side and falling below, the darker areas suggest fuel burning less rapidly, with air.

 

[.Scott]

Why is everyone assuming the cause was in the rocket?

First, let me tell you why "everyone" is assuming that the cause was with the ground support equipment. It's because the giant X drawn by the lens flare falls right at the right edge of the rocket - near the GSE. But this hardly rules out the rocket, as described below.

In the first frame showing flames (frame #1), flames are propagating at least 8.5 feet in no more than 40msec - and that doesn't include the velocity component towards the camera. To achieve this, an ignited fuel/oxygen mix needs to be ejected at hundreds of feet per second. There is no source for this mix at the tower - certainly not in the quantity seen.

The direction of this burst is towards the camera - but since the X is falling to the right of the rocket center, it must be ejecting somewhat to the right.

But we know something more about that mix. For the most part, it does not appear to be "chunks" of anything - rather it is a spray. The primary indication of this is in subsequent frames, frames #2 to #4. What we see in those frame is that the original burst is arrested - presumably by traveling through air, and there is not a sea of fragments emitted from the spray. Although, of course, we do see larger, non-burning fragments.

So that initial (frame #1 and #2) burning mixture is fluid - entirely or almost entirely.

 

[.Scott]

BTW: If we assume that the problem was in the 2nd stage of the rocket, which at this point seems very likely to me, then it introduces this troubling question: Were struts really to blame in last years RUD?

 

[nikkkom]

Were struts really to blame in last years RUD?

I have a feeling you guys are going to rediscover some of the theories already discussed and Nasaspaceflight forum.

Yes, they thought about "maybe it's the same as last years RUD" too. They thought about "maybe it's a COPV failure". They talked about telemetry data (or lack thereof). They did some analysis of the video and visible flying debris. Etc etc etc.

You can save yourself a lot of time by just reading the thread there.

 

[.Scott]

You can save yourself a lot of time by just reading the thread there.

Actually, I am reading the posts in that Forum. And as I said, they are good - well, some are good. I have already posted a graphic from that forum into this thread.
But I don't know about "saving yourself a lot of time". I'm up to post #1000 there - I have a couple thousand more to go. As I find things I think are interesting, I will post them here.

Here is a video from post #991, but bear in mind that everything in the video is well-known to the SpaceX engineers:

 

[mheslep]

...
F9 doesn't have any cryogenic or volatile fuels onboard. It uses RP-1 (a refined grade of kerosene). The visible white venting should be cold oxygen (likely boil-off from LOX tank).

Payload used hydrazine.

 

[mheslep]

... Neither oxidiser nor fuel on its own will release chemical energy.

Though unlike the fuel, as the video you posted indicates, O2 will burn on contact with all kinds of materials including some coatings and metals given an ignition source.

 

[mheslep]

What I want to know is why there aren't super high res cameras covering the launch pad? All I've seen is grainy photos and video.

At 500 or 1000 fps, too many frames to store? Probably reserved for the launch alone, not fueling and test fires. Edit: The videos available fron the Apollo launches taken by cameras on the launch platform are started 5 s before launch and use pricey quartz mirrors.