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In the question: Does the Falcon 9 (v1.1) first stage have an explosive Flight Termination System?

It became clear that the Falcon 9/9R first stage has an explosive flight termination system. Consensus is, that it was NOT deliberately fired on landing after/before the stage crashed into the ASDS barge.

However, if you watch the video, it becomes clear that there is an initial fire when the stage hits the deck, likely the LOX tank splitting and hitting basically anything. (LOX burns with almost anything. I am exaggerating, but you know what I mean). Probably mixed with the Kerosene left over, but we know the volume was fairly low, in the 300 lbs of fuel range.

Then there is a secondary explosion, and then a very kinetic tertiary explosion.

Possibly one of those was the residual TEA/TEB ignitors burning after the engines hit.

But can the FTS system be triggered, by the heat of the fire otherwise. It is an explosive. You can have explosives that are very hard to trigger, but a LOX/RP1 fire can burn pretty hot.

Not knowing the nature of the explosive chosen for the FTS, is it possible it ignited on its own due to the heat of the rest of the goings on?

The video coming in has been amazing! From a chase plane, you can see the stage come right into the barge, land, cold gas system valiantly try to hold it upright, till it tips. This video shows the additional explosions.

There is a great video from the barges perspective here.

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  • $\begingroup$ I didn't think that there is an initial fire at all, actually -- I assumed that was what the engine looked like right after it shut off. For a point of comparison: DM-3 booster test (I realize this is a solid booster, but I've seen other boosters look like this after shutdown, too. Correct me if I'm wrong!) $\endgroup$
    – Nate Barbettini
    Commented Apr 16, 2015 at 20:13
  • $\begingroup$ While I do not know if that was a detonation of the flight abort system it certainly seems like it was--and I rather suspect it was commanded. The rocket obviously hit pretty hard--and the Ariane V rocket decided to blow itself up when it came apart due to excessive aerodynamic forces. I could easily see the same thing happening here. $\endgroup$
    – Loren Pechtel
    Commented Apr 17, 2015 at 1:30
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    $\begingroup$ @LorenPechtel It was not commanded. The FTS was safed shortly after staging. The explosives used in spacecraft are designed only to be detonated by their initiators and are very stable. While I don't know which one they actually use, explosives like C4 can be lit on fire and shot with high powered rifles without exploding. Furthermore, the FTS itself is not a very big charge, just enough to rupture the tanks and disperse the propellants. Anything big enough to make a big boom by itself is just a waste of upmass. $\endgroup$
    – Tristan
    Commented Apr 17, 2015 at 16:00
  • $\begingroup$ @Tristan the boom blew the tanks apart--sounds like what the FTS would do. And I can't imagine why it would be safed after staging in this case--you still have a working rocket with fuel on board, it should have an operational FTS. $\endgroup$
    – Loren Pechtel
    Commented Apr 17, 2015 at 22:13
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    $\begingroup$ You have a working rocket, but the rocket no longer has the ability to endanger personnel or property. That is the sole purpose of FTS -- to protect people and property on the ground. If it doesn't have the energy to reach land or leave the restricted area, there's no need for the system -- an errant rocket can safely crash into the ocean. As far as the big boom itself goes, the tanks blew apart because they fell down and hit the barge, which allowed the RP-1 and oxygen to mix in the presence of flame. $\endgroup$
    – Tristan
    Commented Apr 20, 2015 at 17:14

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It has been pointed out that the debris flying away after the first two explosions, is probably a COPV (Composite Overwrapped Pressure Vessel). These have been problematic, since they are very high pressure tanks, and when they fail, they fail almost explosively. This was probably the COPV venting and throwing itself far away.

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Tthe flight termination system is usually a liner relatively small explosive which rupture the propellant tanks. To explode it need to be initiated by detonators. What explodes in filed rockets are usually pressure vessels which includes pressurized propellant tanks.

Anyway, the explosive contained in FTS can not make spectacular fireball by its oun.

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