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According to this NASA article the tires are inflated to 340 psi (main gear) and 300 psi (nose gear). At landing, there is significant strain, but what about in space? Are the tires exposed to vacuum or are they in a pressurized compartment?

It seems like the stress of being in a very cold and non-pressurized environment would be huge, and completely different from the strain they are under when landing. Why don't the Space Shuttle Orbiter's tires explode in the vacuum of space?

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Standard atmospheric pressure at sea-level Earth is just 14.696 psi. Compare that to 340 or 300 psi (23.14 and 20.42 amt, respectively). The difference in internal tire pressure in Earth's atmosphere and absence of atmospheric pressure in vacuum of space is only 4.3 - 4.9%. Tires would experience far more dynamic pressure environment due to friction heating and pressure of weight of the orbiter during landing (240,000 lbs / 109,000 kg) at contact speeds up to 260 mph (418 km/h) than those ~ 5%. So it's reasonable to assume they were built and tested to withstand more than a pressure difference during a trip to LEO and back.

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    $\begingroup$ Interesting slightly related fact: blowing a tire on landing was one of the more likely failure scenarios for the shuttle. Astronauts routinely practiced extricating themselves from a shuttle that had rolled off the runway into the swamp. Also, the nose gear slap down load was a driving load case for many shuttle payloads. $\endgroup$
    – Erik
    Commented Feb 25, 2015 at 23:04
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    $\begingroup$ Curious choice of words - "slap down" vs "touchdown" $\endgroup$
    – Anthony X
    Commented Feb 26, 2015 at 2:54
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    $\begingroup$ @AnthonyX when you consider the fact that on landing the shuttle was really just gliding really really fast, I think slapdown is probably the most accurate choice ;) $\endgroup$
    – Wayne Werner
    Commented Feb 26, 2015 at 23:01
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    $\begingroup$ Structures are analysed using load cases. The one that simulated a hard nose gear touchdown was called the "nose gear slap down" case at NASA. It was about 9-10 ft/sec if I recall correctly. It was a "3-sigma" case that never happened, although one Commander came close. He didn't get a second chance. If I recall, it is much more likely if you are flying an RTLS abort with a full payload. $\endgroup$
    – Erik
    Commented Feb 26, 2015 at 23:05
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    $\begingroup$ When the shuttle was sitting on its landing gear, it was at a negative angle of attack below the zero lift angle, so there was lift force pushing down in addition to the weight. The politically correct term in Mission Operations was "derotation" rather than "slapdown". Much training was done for this. $\endgroup$
    – Organic Marble
    Commented Apr 23, 2015 at 2:07
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The wheel wells are not pressurized. As @Tildalwave says, pressurization wouldn't make much of a difference.
The wheel wells are insulated to an extent: the wheel well doors are part of the Shuttle's thermal shield, and had to be well-sealed to prevent hot plasma from entering the wheel well.
This meant the temperature swings were less extreme than they'd have been if the tires were exposed to space. The tires were tested for temperatures between –40 °C (–40 °F) and +55 °C (+130 °F). That sounds like a lot, but tires on Earth routinely reach these temperatures.
Rubber can withstand much lower temperatures without problems: its glass transition temperature is -70 °C.

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  • $\begingroup$ I think one of the first signs of trouble in the Columbia disaster was when they got a warning that they had lost pressure in both left main tires. This was just before communications was lost. $\endgroup$
    – Howard Miller
    Commented Apr 17, 2016 at 20:56
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    $\begingroup$ This happened because the sensor wires burned through, not because the tires actually lost pressure at that point. A gear/tire problem was an early candidate for the cause though; we briefed the CAIB on the system. $\endgroup$
    – Organic Marble
    Commented Apr 18, 2016 at 10:38

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