Did the Apollo astronauts describe any differences in how it felt in the CM as it passed between the hypersonic, supersonic, transonic and the subsonic zone? Did the CM shake more or less in different zones? Was the type of movements different through the descent?


1 Answer 1


The best sources for this kind of thing might be the technical crew debriefings done within days of each flight.

I've looked at a few of them and they don't describe any shaking; they frequently comment on the smoothness of reentry, in fact. They do discuss (low-frequency) oscillations in a few cases, i.e. the capsule rocking back and forth due to aerodynamic effects.

Apollo 11:

ALDRIN I thought the g constant was quite smooth.

COLLINS I thought it was smooth also.

Aside: this debrief also includes a description of the appearance of the ionization trail which might bear on another question you had:

COLLINS Along about .05g, we started to get all these colors past the windows; Buzz took some movies, which we looked at last night. They don't really show what the human eye sees. Around the edge of the plasma sheath, there are all varieties of colors- lavenders, lightish bluish greens, little touches of violet, and great variations mostly of blues and greens. The central core has variations on a orange-yellow theme. It's sort of a combination of all the colors of the rainbow really.

Apollo 12:

CONRAD Oscillations. I thought, boy, the spacecraft was steady as a rock. It's just like the simulator. I found that hard to believe and even made the comment I wanted to see whether the spacecraft was that steady and stable during reentry.

GORDON It really is.

CONRAD And it was just like the simulator. You get in the transonic region, and if you get it to oscillate a little bit, you get some more RCS firing.

The Apollo 17 crew does mention noise:

EVANS Communications - From 90 000 feet until about main parachute deployment, I had a time trying to hear Jack. There was a lot of background noise.

EVANS It just gets noisy in the spacecraft from about 90 000 feet on down. Once you get the altimeter off the peg, I had a time hearing you call out.

SCHMITT I was shouting, too. I realized you were having trouble hearing. There was noise. It must have been air noise coming through the hull.

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    $\begingroup$ Are there any deceleration measurement graphs available? But telemetry might have been discontinued during the hot phase of reentry. Data recording within the command module was very limited at that time. $\endgroup$
    – Uwe
    Commented Dec 14, 2018 at 16:36
  • $\begingroup$ I assume so; the data recorder in the CM was adequate. $\endgroup$ Commented Dec 14, 2018 at 16:39
  • $\begingroup$ Here's one, surprisingly a multiple-peak affair from Apollo 10: history.nasa.gov/SP-368/p135b.htm -- doesn't look like raw data though. $\endgroup$ Commented Dec 14, 2018 at 16:46
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    $\begingroup$ The Apollo 11 data is here -- two strong peaks, no constant 4g. Don't know why the discrepancy; whole thing must be a hoax after all. $\endgroup$ Commented Dec 14, 2018 at 22:38
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    $\begingroup$ I love it when they say it was just like the simulator. $\endgroup$ Commented Feb 19, 2020 at 17:51

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