This question inspired by a short Twitter exchange with @thehighfrontier about clothing for Spaceship Two passengers.

Crews of particularly high-flying aircraft wear full pressure suits. So do astronauts during ascent and descent. But once spacecraft had room for astronauts to do so, it seems like they started to favor shirtsleeves once they were in orbit.

What's the rationale for this? Is depressurization somehow riskier in these other flight regimes?


1 Answer 1


Ascent and descent are relatively dynamic. Large amounts of energy are being transformed and redistributed very rapidly and violently. On ascent in particular, there is the potential for the booster to disassemble itself in an uncontrolled manner, which could easily cause major damage to the crew capsule; descent and reentry is a little safer, but the forces the capsule is being subjected to are still rapidly changing and non-uniform.

Once in orbit, out of the atmosphere, and coasting in unpowered flight, the risks of depressurization are rather reduced. A puncture of the hull due to space debris is the main risk. In most cases this wouldn't lead to immediate total depressurization (particularly on a station with a lot of internal volume relative to its impact-target cross section).

Since it's impractical to remain in a bulky and uncomfortable pressure suit for days at a time, the suits are worn only for the short periods where the risk is highest.

In at least one case, on Apollo 7, when the crew was suffering head colds, they opted not to wear their helmets for the descent so they would be able to equalize their middle-ear pressure by pinching their noses and blowing; they must have judged the risk of losing cabin pressure to be very low.

  • $\begingroup$ Do you think this reasoning also carries over to the various high-flying aircraft, e.g. the WB-57, U-2, SR-71? Or am I trying too hard to cross the Aviation and SE stackexchanges? $\endgroup$
    – Erin Anne
    Commented Oct 17, 2019 at 3:41
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    $\begingroup$ Both the U-2 and SR-71 maintained very low cabin pressure (26000-28000 feet altitude equivalent, about 33% sea level), so not wearing a pressure suit simply wasn't an option; they also only stay at altitude for hours at a time instead of days or months. I don't know the particulars of why those planes didn't maintain higher cabin pressure. Crewed spacecraft have always maintained breathable cabin air (either mixed at sea level pressure or pure oxygen at low pressure). $\endgroup$ Commented Oct 17, 2019 at 4:42
  • $\begingroup$ Shuttle crews closed their visors at launch to protect against bird strikes breaking the windows. They opened the visors at SRB sep because the altitude was high enough to minimize the risk. They didn't close them for the entire ascent because when they were closed, the suits leaked O2 into the cabin atm. $\endgroup$ Commented Oct 17, 2019 at 23:01
  • $\begingroup$ "Opted not to", was there backlash for this or did they get the go-ahead to do so? I didn't think a lot of things were optional. $\endgroup$ Commented Oct 18, 2019 at 14:47
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    $\begingroup$ @MagicOctopusUrn Yup. As described in the Wp article, there was a lot of friction between the A7 crew and mission control, and Eisele and Cunningham were sidelined from future missions (Schirra had already announced his retirement). The mission commander can order the crew to perform re-entry wearing boxer shorts on their heads, but they have to answer for it once they're on the ground. $\endgroup$ Commented Oct 18, 2019 at 15:42

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