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I realize that this is a hot take, less than twenty-four hours later at the time of posting, but is any technical detail known about why the core engines failed to restart, causing the crash?

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The answer given by Musk in the post launch conference call was that they ran out of the TEA-TEB igniter fluid, which is used to start or restart the engines.

On the ground, the TEA-TEB is externally provided for launch to start all 27 engines.

For landing attempts, only 3 engines are equipped with TEA-TEB to allow restarting.

It is a little hard to hear, but Musk seemed to say they ran out of Boron, which would imply the TEB specifically.

SpaceX just tested a three engine landing attempt that worked (sort of, there was no ASDS underneath it to land on, but it landed soft enough that they found the booster floating on its side) so they know how to do it. Likely there is some difference with the Falcon Heavy core stage and the standard Falcon 9 that may account for this issue.

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    $\begingroup$ I believe TEA-TEB is one substance, not separate TEA and TEB, implying that "boron" was just a shorthand. $\endgroup$ – Russell Borogove Feb 7 '18 at 19:44
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    $\begingroup$ @RussellBorogove I've always assumed it's a eutectic mixture. That is to say, a mixture whose freezing point is lower than its components, like salt and water. I can't think of any other advantage to using a mixture. $\endgroup$ – Level River St Feb 7 '18 at 20:00
  • $\begingroup$ Clark's Ignition! says that the first production use of TEA-TEB in Atlas rockets was 15% TEA, 85% TEB, but doesn't say anything about how that mix was arrived at. $\endgroup$ – Russell Borogove Feb 7 '18 at 20:19
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I believe that there was a failure in procedures on the ground to put Tea mixture in the core booster. It ignites instantly so I don't believe they ran out for the core but not the two other boosters.

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  • $\begingroup$ Saying something ignites "instantly" doesn't make any sense. In any case, the center core reignited previously in order to slow down and reenter (and in fact reports are that one of the three engines reignited for landing, which was not enough). $\endgroup$ – Nathan Tuggy Mar 16 '18 at 1:42

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