SpaceX Needs Us!

  • #1
127
24

Main Question or Discussion Point

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.
 
  • Like
Likes mechpeac and HyperTechno

Answers and Replies

  • #2
Student100
Education Advisor
Gold Member
1,649
416
Did Musk also release detailed drawings of the Falcon 9 and minutes of the test? With just a video there's no way to come to any realistic conclusion that isn't pure conjecture.
 
  • Like
Likes Fervent Freyja
  • #3
127
24
Musk is asking if anyone else has photos or videos, so conjecture away! They have all the technical info, and they are stuck and need help. The people here might make a difference for them, by seeing things differently.

Try it, for real. What can you deduce from the video? What do you see?
 
  • #4
jim hardy
Science Advisor
Gold Member
2019 Award
Dearly Missed
9,839
4,869
I dont know how to single frame Youtube, arrows only give me 1/4 second increments.
here's best i can get
spaxex1.jpg
 
  • Like
Likes mechpeac
  • #5
127
24
This is the 'raw' site: You can't use YouTube to advance by frame. Use this link: http://rowvid.com/?v=_BgJEXQkjNQ
(You can use that site for other videos too. )
Or http://anilyzer.com/

With that said, you got the first frame of the explosion, or what I get, at least. But using rowvid.com is easy.

So, where do you think the explosion started?
 
  • Like
Likes Pepper Mint
  • #6
jim hardy
Science Advisor
Gold Member
2019 Award
Dearly Missed
9,839
4,869
Where'd it start ? well it's hard to say
My best guess follows.


i find anilizer just typical recalcitrant software, a bundle of excuses to not do anything.

But using rowvid.com is easy.
well! What a pleasant surprise rowvid WORKS GREAT ! Sure beats trial and error on Youtube.

Okay that was first frame at 71.74
Second frame at 71.78
spacex2.jpg

Seems to me a kerosene leak would have run down and set the whole rocket afire, slowly like charcoal lighter. Clearly this was a kerosene & LOX mix burning,
spacex3.jpg

Whole 2nd stage got engulfed in a fireball and blew apart.
Would've taken failure of both tanks to let fuel and LOX mix
so
My guess is 2nd stage engine somehow got a start signal .
See my signature ..............

what's your thoughts?
http://www.spacex.com/falcon9
http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf
https://en.wikipedia.org/wiki/Falcon_9
Both stages use a pyrophoric mixture of triethylaluminum-triethylborane (TEA-TEB) as an engine ignitor.[51]
[see msds's linked below - old jim]

SpaceX uses multiple redundant flight computers in a fault-tolerant design. Each Merlin rocket engine is controlled by three voting computers, each of which has two physical processors that constantly check each other. The software runs on Linux and is written in C++.[52] For flexibility, commercial off-the-shelf parts and system-wide radiation-tolerant design are used instead of rad-hardened parts.
i've not yet found the tank that holds the ignitor fluid. See its MSDS 's here
http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=US&language=en&productNumber=257192&brand=ALDRICH&PageToGoToURL=http://www.sigmaaldrich.com/catalog/product/aldrich/257192?lang=en
http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=US&language=en&productNumber=257168&brand=ALDRICH&PageToGoToURL=http://www.sigmaaldrich.com/catalog/product/aldrich/257168?lang=en
Looks like it'd burn if it got loose. That's another possible single failure.

By the way - THANK YOU for the pointer about single-stepping at rowvid


old jim
 
  • Like
Likes Dr. Courtney and Pepper Mint
  • #7
Nidum
Science Advisor
Gold Member
2,990
848
Just looking at the basic images may be of limited use .

More effective would be to find ways of processing the primary images to give a series of new images each covering a restricted range of light wavelengths .

Breaking down into primary colour images is certainly possible and that would be useful but ideally ways might be found of getting some IR images as well - even poor quality ones would be very useful indeed .
 
  • #8
18,142
7,647
If a PF member could help that would be incredible! PF team assemble! :)
 
  • Like
Likes mechpeac and HyperTechno
  • #9
RonL
Gold Member
1,097
215
Using the four light rays in that first picture seems to show an X as in x marks the spot. :rolleyes: pretty much where the steam or smoke was showing the frame before.
 
  • #10
It looked like the fuel tank... I agree with Jim hardy
 
  • Like
Likes HyperTechno
  • #11
Filip Larsen
Gold Member
1,256
183
For what its worth, Scott Manley has posted a nice commented video analysis:
 
  • #12
.Scott
Homework Helper
2,517
897
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 Fig.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.
 
Last edited:
  • #13
berkeman
Mentor
57,306
7,296
Musk is asking if anyone else has photos or videos, so conjecture away!
If a PF member could help that would be incredible! PF team assemble! :)
So the Mentors have been discussing this thread, and the thread should be fine as long as it sticks to the established facts and the science behind the rocket. The PF rules obviously apply, so please be like Jim in your posts, and show the science behind your speculations about what may have happened.

Jim -- could a false engine start signal have happened without it showing up on telemetry? There are a couple potential causes of a false engine start signal detection by the module, but hopefully SpaceX has done enough immunity testing to rule that out...
 
  • #14
127
24
As a side note on rowvid.com, I was puzzled by that domain name, so I looked into it.
From http://hackersome.com/p/CalumJEadie/rowvid-version-0
"RowVid was originally created by Calum Eadie, Andrew Ratomski and https://twitter.com/busterlj [Broken] at an Entrepreneur First Hackathon, to help rowers analyse training and race videos.
Since then it has evolved into general purpose player for frame by frame and slow motion playback of any YouTube video."

It makes sense now. I assume they were rowers at Cambridge. See https://www.linkedin.com/in/calumjeadie [Broken]
 
Last edited by a moderator:
  • #15
Stephen Tashi
Science Advisor
7,118
1,300
It might be useful to have some links to videos of other similar sized explosions that had known causes.
 
  • Like
Likes mechpeac
  • #16
Tom.G
Science Advisor
3,177
1,912
Rocket-02a.jpg


Here is what it looks like with the intensity range restricted so the bottom half of the intensity range is compressed.
The contour lines are brightness/color contours.
After viewing the video forward, backward, and stop-frame, the ignition point appears to coincide with the crescent shaped area at the arrow head. This is partially supported by a subtle color change within the crescent area (less Blue).

Visually, from the video, the initial flame front seems to travel toward the 7 o'clock position but rapidly changes to about the 5 o'clock position. Based on the above image, the origin is 3 to 3.1 nose cone diameters from the the nose cone tip at the right edge of the rocket.

Viewing the video backwards, the fireball seems to converge to a point 3.3 diameters from the tip, at the center of the rocket body.
 
  • Like
Likes Fervent Freyja and TheBlackAdder
  • #17
Jonathan Scott
Gold Member
2,294
991
Could this be a variant of the same failure as before? If a helium tank support strut broke because of buoyancy forces during loading of the oxygen, the excess pressure in the LOX tank could split the second stage, releasing both fuel and oxidiser and also generating enough heat to ignite the mixture.
However, in that case I'd have expected the tank pressure telemetry to have recorded enough information to make that clear.
 
  • #18
Jonathan Scott
Gold Member
2,294
991
After thinking about it some more, it seems likely that something to do with the helium tank could be relevant, as a sudden failure would be able to rupture the second stage very abruptly in a way which would open up both the LOX and the RP-1 tanks. The fact that the LOX tank was only passing 70% full at the time of failure might be enough to rule out anything relating to buoyancy (but I don't know the details). If a strut broke as before, I would have expected a larger time interval between the initial problem and the rupture.
 
  • #19
Dotini
Gold Member
621
229
Would a cosmic ray passing through the tanks be enough to cause concern?
 
  • #20
Nidum
Science Advisor
Gold Member
2,990
848
The oxygen tank on Apollo 13 exploded because a faulty electrical device in the tank sparked .
 
  • #21
34,281
10,322
Would a cosmic ray passing through the tanks be enough to cause concern?
Every second, about 100 muons cross every square meter of the surface of Earth. No, those are completely irrelevant.

I guess SpaceX will monitor all future static fire tests and launches with a high-speed camera (maybe they do that already).
 
Last edited:
  • Like
Likes mheslep
  • #23
127
24
  • #24
jim hardy
Science Advisor
Gold Member
2019 Award
Dearly Missed
9,839
4,869
spacex4.jpg


pieces flying away


Jim -- could a false engine start signal have happened without it showing up on telemetry? There are a couple potential causes of a false engine start signal detection by the module,
Anyone know how much delay there is in the telemetry ?



.
 
  • #25
127
24
Jim, 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.
 

Related Threads on SpaceX Needs Us!

Replies
35
Views
4K
  • Last Post
Replies
13
Views
1K
  • Last Post
4
Replies
81
Views
6K
Replies
3
Views
936
Replies
12
Views
1K
Replies
7
Views
811
Replies
15
Views
7K
Replies
11
Views
244
Replies
12
Views
2K
Replies
19
Views
1K
Top