In his tweet Elon Musk said: "Rocket is extra toasty and hit the deck hard (used almost all of the emergency crush core)"
What is he talking about?
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asked Jun 24, 2017 at 11:40
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1$\begingroup$ related: Why were three engines used for the F9 1st stage landing burn (BulgariaSat-1)? $\endgroup$– uhohCommented Jun 24, 2017 at 16:04
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2 Answers
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The landing legs have a honey-comb filler that can compress to absorb significant energy of a hot landing.
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1$\begingroup$ Additional crush core information from a previous landing (Thaicom-8) can be found in this answer. $\endgroup$– uhohCommented Jun 24, 2017 at 14:23
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3$\begingroup$ Hah, I was about to ask if SpaceX was hand drafting technical diagrams, but those are from Apollo. $\endgroup$ Commented Jun 24, 2017 at 17:42
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$\begingroup$ What if the distribution of forces between legs is uneven? Do you end up with uneven leg lengths, or does this imply that there is secondary (less robust) suspension to keep things balanced? $\endgroup$– spenderCommented Jun 25, 2017 at 17:10
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$\begingroup$ From the video footage after landing it looked to me like the legs did indeed end up with uneven lengths. $\endgroup$ Commented Jun 25, 2017 at 18:08
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$\begingroup$ I'm assuming that by 'hot', you mean fast? Might want to clarify this. $\endgroup$ Commented Jun 26, 2017 at 9:52
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The legs are designed to bounce and take some impact on landing. For further absorption of shock they include non-reusable crush cores, that deform and absorb the energy but cannot bounce back.
They are made replaceable and it is preferable to use them up than to have the stage hit the deck.