# Can we create a vacuum inside an EVA suit when the outside is pressurized, will it implode?

EVA suits are specially designed spacecrafts for astronauts during spacewalks. I can say for sure, it can handle the following cases of pressurization of the system:

• Pressurized inside, but vacuum outside - This is the usual purpose of the suit during spacewalks.

• Pressurized inside as well as outside - This case is observed when astronauts train in the Neutral Buoyancy Lab (NBL).

• Vacuum inside as well as outside - Doesn't make any difference as there is no net pressure. So there is no stress on the system.

Even though this lacks any practical application, can an EVA suit handle the stresses of vacuum inside but pressurized outside, unlike the usual opposite (pressurized inside but vacuum outside)? Or in other words, can we create a vacuum inside an EVA suit (by pumping out gas from the suit) when the outside is pressurized or will it implode (explode inwards)?

• Related but not the same : What does “double vacuum pressure” mean in space-suit testing? Commented Nov 6, 2019 at 8:02
• Implosion has a specific meaning, and normally involves a rigid container suddenly failing under vacuum pressure. Being mostly flexible a space suit would basically vacuum pack itself into the helmet and other solid elements. Commented Nov 6, 2019 at 8:24
• @GremlinWranger, Thanks. Forgot spacesuits have flexible soft parts (gloves - the only thing I could think of). Others can't bend inwards, I think. Will the rigid sections be able to handle the stresses? Commented Nov 6, 2019 at 8:40

The shuttle/ISS suit is protected from excessive crush loading by a negative pressure relief valve (NPRV). This valve opens when the outside pressure exceeds the inside pressure by 0.8 psi and allows gas to flow into the suit.

This could come into play during repressurization of the airlock.

The following image shows the NPRV and its position in the EVA suit's backpack:

Sources:

• Thanks for your answer. So simply it means, it can't withstand the negative pressure loads (beyond certain limit), am I right? Further, could you please explain how this case could occur in the airlock, as I think the suit will always be pressurized. Commented Nov 6, 2019 at 15:42
• The final airlock pressure is at ~15 psi, the suit is at ~4 psi during EVA. Commented Nov 6, 2019 at 15:45
• Thanks. Will you permit me to add the image of NPRV from the paper? Commented Nov 6, 2019 at 15:52
• Of course! Thanks for improving the answer. Commented Nov 6, 2019 at 15:53
• The protection of the astronaut wearing the suit against excessive crush loading is very important.
– Uwe
Commented May 24, 2020 at 22:49

A spacesuit is designed to be strong in tension, not compression. Most parts of a space suit are soft. If you try to suck all the air out of a space suit at sea level, the suit will simply compress flat.

Sea level air pressure is 14.7 pounds per square inch. So every square foot of space suit would have to hold back a force of 2000 lbs. You would need a completely rigid suit to be able to hold a vacuum.

Even railway tanker cars need pressure valves to keep them from drawing too much vacuum inside (for example, if a tanker is filled hot, then cools way down, the volume of the contents may shrink, creating a vacuum). Without these check valves, a tanker car with 1" thick steel walls can crush flat with as little as 3 psi difference between the interior and exterior.

It would be possible to make a hard suit that can hold a vacuum. It would have to be engineered specifically for that. Current spacesuits are a mix of hard and soft regions, and would not hold a vacuum against the force of the atmosphere.