We often see on the SpaceX launch streams that they are spraying water on the deck of the ASDS where the booster will land: enter image description here There are multiple potential reasons to do this which come to mind:

  • Decrease the scorching of the deck during landing
  • Fresh water to hose down any sea water that got on the deck to prevent booster contamination with corrosive salt water
  • Testing of fire-fighting gear
  • ... ?

Is the real reason known to the public, or is it all just speculation? Why do they start spraying so far in advance? Wouldn't it be sufficient to begin after launch?

  • $\begingroup$ Probably the same reason why they spray it during the launch? As a sounds suppression system most probably. The corresponding wikipedia page says that shockwaves are generated by the supersonic exhaust colliding with the ambient air, and the energy, which the platform may reflect, can potentially damage the platform, the vehicle etc. $\endgroup$ Commented Jun 9, 2022 at 10:41
  • $\begingroup$ But the first potential reason you mention also seems very plausible. At around 7:44 in this video of the falcon heavy boosters landing back on the land based pads shows that the pads already have water on them as the boosters approach, and the water is not being sprayed during the landing. So it might as well be just to protect the pad surface. $\endgroup$ Commented Jun 9, 2022 at 10:47
  • $\begingroup$ @pathfinder_EOS No way this is for sound suppression. They no longer spray the water when the booster is landing. $\endgroup$
    – JohnEye
    Commented Jun 15, 2022 at 8:32
  • $\begingroup$ Yes. As my second comment suggests, it is probably not for sound suppression but to protect the pad in some way. In the recent missons, when the booster lands on the drone ship, for example Nilesat 301 and this starlink launch, the pad already seems to have water on it as the booster approaches. For Transporter 5. however, the booster lands on a land based pad and there seems to be no water. $\endgroup$ Commented Jun 15, 2022 at 12:03


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