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It's becoming clear now that the 4/20 launch devastated the launchpad, leaving a massive crater and flinging debris - perhaps into the booster itself.

But why did this not happen during test firings of the Super Heavy booster when the same stresses were put on the pad?

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  • $\begingroup$ Why do you assume that firing 31 engines for 2 seconds at 50% thrust with a mostly empty booster and no Starship on top puts the same stresses on the pad as firing 33 engines for 6 seconds at 90% thrust with 5000 tonnes of vehicle and propellant sitting on the OLM? $\endgroup$
    – Jörg W Mittag
    Apr 22 at 11:14
  • $\begingroup$ @JörgWMittag ok so they didnt do it all full power. $\endgroup$
    – Abdullah
    Apr 22 at 11:32

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The same stresses weren't put on the pad, but pad damage did happen during the test firings. SpaceX repaired and tried to reinforce the pad with a specialized concrete called FONDAG RS which "can be used in severe duty industrial concrete applications that may require refractory performance." If you want to go into depth on the repeated test firings, repeated concrete rain, and repeated pad rebuildings, see e.g. the CSI Starbase video "SpaceX's Major Concrete Problem + Water Deluge Construction Begins at Starbase".

Musk tweeted on 21 Apr

3 months ago, we started building a massive water-cooled, steel plate to go under the launch mount.

Wasn’t ready in time & we wrongly thought, based on static fire data, that Fondag would make it through 1 launch.

Looks like we can be ready to launch again in 1 to 2 months.

Recall also that the 31 engine static fire was "less than half of the booster's capability" but it still caused an audible post-fire rain of debris (from NASASpaceflight's 31 engine static fire coverage) (though possibly more from the OLM itself than the pad).

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  • $\begingroup$ I think SpaceX was facing an impossible engineering choice. Because of a very shallow water table, they could not create a proper Flame Trench. They would have to build a 'bathtub' with water retaining walls around the launch tower. But that would put a stop to all launch tower activity for a year or more. $\endgroup$
    – TheMatrix Equation-balance
    Apr 22 at 16:10
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    $\begingroup$ Well, now they have a nice hole to start building their bathtub in. $\endgroup$
    – Darth Pseudonym
    Apr 22 at 20:39
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    $\begingroup$ there's a reason the big launch pads at KSC are on built-up mounds. And way, way bigger than the Starbase complex. $\endgroup$
    – Erin Anne
    Apr 22 at 21:09
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    $\begingroup$ this was yet another example of "they don't make 'em like they used to" (Was LC39A built with a rocket much larger than the Saturn V in mind?) $\endgroup$
    – uhoh
    Apr 23 at 19:47
  • $\begingroup$ I'm not sure why a shallow water table is a problem if you want to have a bathtub! ;-) $\endgroup$
    – Peter - Reinstate Monica
    Apr 24 at 8:38

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