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As stated elsewhere, the soundwaves formed by a rocket launch are powerful enough to do structural damage to the spacecraft during launch. How are astronauts protected against the soundwaves, or why is the crew capsule not affected by the extreme sound, especially at subsonic speeds?

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There are several barriers between the engines and the astronauts.

  1. The capsule walls. The pressure vessel is covered in insulation on both sides. This is mainly heat insulation, but provides a barrier to sound too. This could easily provide 30 dB of reduction.
  2. The space suit helmet. Again, a hard shell with insulation and padding inside. Another 20-30 dB of reduction.
  3. They may have noise-insulating headphones (in-ear), which can provide another 20 dB of reduction. Not sure about this, I'll try and find a reference later.

The noise level at the top of the rocket is around 130 dB at launch, dropping quickly as the rocket takes off and the amount of sound reflected by the ground reduces. So layers 1 and 2 are already enough to get to a non-dangerous noise level.

NASA has standards for noise levels (NASA-STD-3001 : Acoustic Limits for Launch, Entry, and Abort Phase) in the cabin during a mission. They indicate a maximum noise level during launch of 105 dBA continuous, 140 dB peak, 150 dB for infrasonic noise (1-20 Hz).

Sound level near the engines is in the region of 200 dB. With the water deluge system in use, sound level in the payload bay peaks at 142 dB.

Noise level at the Shuttle cabin level (outside) is 12 dB lower than at the base of the stack (page 9).

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  • $\begingroup$ In ear and over ear headphones could use ANR (Active Noise Reduction) as well, that's good for 20db as well. $\endgroup$
    – GdD
    May 15, 2018 at 7:59
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    $\begingroup$ Reducing reflection of sound by the ground is another method. A water sound supression system was used for the launch of the Shuttle, see this question. $\endgroup$
    – Uwe
    May 15, 2018 at 12:57
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    $\begingroup$ Even with a sound suppression system, the acoustic loading on a payload is on the order of 130 dB, so you need 30-50 dB of reduction to get to a safe level for humans. $\endgroup$
    – Hobbes
    May 15, 2018 at 13:30
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    $\begingroup$ Can't dispute Hobbes' dB reduction nums, but I can say that, during my Space Shuttle mission launch (and, bear in mind that Space Shuttle launches were extremely noisy events, even relative to other launch events), all I noted was a muted roar when the solids lit. I was kind of surprised by that. There was a lot of stack between the crew and the torch. On a side note, I've never heard of noise-canceling headphones ever being used for this purpose... $\endgroup$
    – Digger
    May 16, 2018 at 22:29

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