In real life, astronauts spend upwards of a day preparing for spacewalks, mainly acclimating to the lower pressure in their suits and adjusting to breathing pure oxygen. If they don't do this, and instead just don a suit and hurl themselves out the airlock, they will get the bends and quite possibly die. And unfortunately, using the same atmosphere as a suit inside the station or ship so the acclimation can be skipped is a no go, as pure oxygen plus even a single spark equals fiery death.

My question is pretty simple: Is there a way I could get around this and allow people in my world to go out into hard vacuum at a moment's notice?

Edit: Thanks all! A combination of hard exoskeleton suits for military use and mechanical counterpressure suits for civilians sounds ideal for my world, but there's plenty of other fantastic answers ITT.

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    $\begingroup$ Say, to fix heavy combat damage that needs immediate attention - which can definitely happen in this setting. Drive cone got clipped? Better patch that before the enemy catches up. Let's say they have no more than five minutes to get out, and faster is better. $\endgroup$ Nov 2, 2020 at 22:17
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    $\begingroup$ The answer to this question will always be "yes." I can use a hard suit (as already discussed in answers), which is just a small space ship, I can use a Clarkean Magic magnetic shield, I can use a soft suit combined with a pharmaceutical that conditions the body in under 3 minutes! I suspect that given time we could come up with a dozen ways to explain this - but each solution has pros and cons. What are you really asking? What is the specific job that must be done? How long must they be outside? How much exertion is involved? We need details to be objective. VTC:ND until provided. $\endgroup$
    – JBH
    Nov 2, 2020 at 22:51
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    $\begingroup$ Do you need an actual space "walk"? If not, the pods from 2001: A Space Odyssey would probably fit the bill. Hop in, close the hatch, and zip out to fix stuff using robot manipulator arms; no fancy prep required. $\endgroup$ Nov 2, 2020 at 23:11
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    $\begingroup$ WHY assume pure oxygen in the spacesuit? That is the foundation of your problem, and is a false assumption. The reason current spacesuits use pure oxygen is because it is harder to build a flexible spacesuit for full pressure . Harder, not impossible. $\endgroup$
    – user79911
    Nov 3, 2020 at 6:54
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    $\begingroup$ "And unfortunately, using the same atmosphere as a suit inside the station or ship so the acclimation can be skipped is a no go, as pure oxygen plus even a single spark equals fiery death." I'm fairly certain that you refer to the Apollo fire here. That accident happened with 1.2 atm O2 atmosphere. Around 0.2 atm is perfectly fine. Sure fire will burn a bit hotter and be a bit more dangerous, as the thermal inertia of the N2 is gone, but otherwise everything is save. $\endgroup$ Nov 3, 2020 at 14:46

9 Answers 9


Hard Suit Exoskeleton

enter image description here

The suit maintains the same air pressure as inside the ship and the powered exoskeleton restores the ease of movement. Soft flexible spacesuits would have the problem of blowing up like a balloon and the additional pressure making the limbs harder to move but a hard suit avoids these problems.

Robotic Avatar

enter image description here

By using an avatar, a person can go outside without going outside. This would be the fastest solution as avatars can be stored outside the ship and accessed at a moment's notice. It's also the safest solution as you can get another avatar if one gets killed.

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    $\begingroup$ Drone. Why leave the ship at all? +1. $\endgroup$
    – JBH
    Nov 2, 2020 at 22:55
  • $\begingroup$ Theoretically people would be in life support statis capsules and not have to leave. Brain is plugged into the ship so you can run it from there and anything requires a physical presence is just an avatar. The ship could be destroyed but the crew would survive unless the capsule took a direct hit. $\endgroup$
    – Thorne
    Nov 2, 2020 at 23:03
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    $\begingroup$ @Thorne this, however, does create a massive single point of failure. Somebody bumps against the brain vat rack and suddenly the ship becomes a floating bit of mostly uncontrolled debris ready to be taken over without any trouble. The remaining AIs will be easily thwarted. $\endgroup$ Nov 3, 2020 at 8:02
  • $\begingroup$ One can use full atmospheric pressure inside a flexible suit as well. The only parts that need to be "hard" are some of the joints, mainly the fingers, elbows, and shoulders. You can get by without your legs for a space walk since you are not really using them to stand or grip. With hard joints you won't need any assistance to move. $\endgroup$
    – user4574
    Nov 4, 2020 at 1:53
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    $\begingroup$ @JohnDvorak Brains are always a point of failure in any mission of any kind. I'm not sure how being in a capsule changes that. Thorne's comment didn't even require that the brains all be in the same capsule, or even the same area, so you could have the same amount of redundancy that brains normally have in freely moving bodies. $\endgroup$
    – jpaugh
    Nov 4, 2020 at 16:24

Use a mechanical counterpressure suit.

These are space suits designed for a lower profile. By using mechanical rather than atmospheric pressure across most of the skin (except for the face), they eliminate the need to maintain the same pressure in the helmet and suit body.

There's nothing wrong with the atmospheric mix used in the station for breathing purposes. (Obviously, or it wouldn't be used in the station!) However, pressurizing a traditional suit to that pressure would render it extremely stiff and impossible to move around in while outside the habitat. Because a mechanical counterpressure suit only has air in the helmet, the pressure there is not a barrier to activity.

  • $\begingroup$ The MIT Bio-Suit, in your link, is a fascinating addition to the story of space-suits, especially in this sort of an emergency setting. $\endgroup$
    – Cort Ammon
    Nov 3, 2020 at 16:34
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    $\begingroup$ Extra points for justifying the tight fitting space suit trope :) $\endgroup$
    – ojs
    Nov 5, 2020 at 7:59

You a have a shift system where you allways keep some crew members suited up and ready to go. Its a bit of a wasteful in terms of people resources (as all they could do is float around while suited up) but this would not need any new technology.

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    $\begingroup$ +1 for being possible with current tech. I'd also add that these on-shift members could be working in an area of the ship/station where the pressure of the rooms themselves are lower (so no suit is needed during acclimation and they can keep being productive), and they are wearing pure oxygen masks (to avoid fiery death mentioned by OP) $\endgroup$
    – automaton
    Nov 4, 2020 at 15:37
  • $\begingroup$ Probably, if that was a habit, we would figure out ways for them to do something besides float around. $\endgroup$ Nov 5, 2020 at 21:58

An alternative

@Thorne's mention of using a drone caused me to ask some questions. I upvoted his answer, but here's an alternative.

Assumption: The human being actually needs to leave the ship. Whether they just want to embrace the ultimate emptiness of space to the greatest degree or whatever the task to be done is, it can't be done by a drone of any shape or kind regardless how futuristic the tech gets (and if we use James Cameron's movie Avatar as an example, it can get very futuristic).

Assumption: The human being actually needs full movement. This means we can't use a human-shaped space ship. The hard suit is a fun idea, but it has fundamental problems, not the least of which is every articulated joint means a pressure weakness. That space under the armpit is incredibly hard to armor in a way that would keep pressure under control. Those dudes from Starcraft? Yeah... unless you separate their arms from their shoulders there's no way to pack that much torso and arm armor on. Besides, hard suits are boring! They've been used since the 1940's! Who wants to do what almost every scifi writer has done for 80 years?

My Proposal

1. Who says the mouth is needed for oxygen?

People who live in space are a unique breed. They always have been! And one of those reasons is they have these odd ports in their backs — one each on the left and right side of the body. Those ports connect the lungs to some of the coolest juju ever invented by Walker Space LLC (𝅘𝅥𝅯 Never go to space without your Waaaaalkeeer! 𝅘𝅥𝅯). The backpack on your suit contains compressed liquid atmosphere, which is normalized and move into and out of the lungs at a constantly monitored rate and pressure to keep them happy during your space walk. But that's not all!

There's two smaller ports in their back on the left and right of the heart that connect directly to the veins and arteries around the heart. Blood is drawn out, oxygenated, and put back into the body such that between the two systems no atmospheric suit is needed at all. The lung connection keeps your body's natural desire to "breathe" entertained while the circulatory connections actually keep you alive. And because we've taken the lungs out of the picture, the system can actually keep your body happy longer by including basic nutrients.

Because going to the bathroom on a space walk is so... inconvenient....

2. The suit's primary purpose is to keep you inside... and warm...

Relieving the suit as a necessary component for oxygenating the body means that it's nothing more than a heated elastic sock. The heat is obvious... but that elastic sock part might not be.

Those old-fashioned suits had to keep the space walker breathing as well as warm and contained. The body is designed to push outward against the skin to compensate for atmosphere pushing down onto the body. The situation isn't quite as bad as movies like Schwarzenegger's Total Recall, etc. But ugly things happen to the body when there isn't enough pressure outside.

This new suit has nothing at all to do with oxygenating the body — that's done through those ports we discussed. That means the suit is nothing more than an elastic sock that creates pressure against the body.

And this is great news! Because it means the suit can allow for more tactile experience and acrobatic response. No hinges, no seams, no bulky gloves. What's the point? You feel normal and can manipulate the world around you as normal.

3. But we still need to deal with radiation. And really strong sunlight.

Because no matter how well we deal with oxygenating the body, keeping the solar wind and various unhealthy radiations away from the body is still a problem. But we're dreaming, so we can claim the elastic body suit is radiation-proof.

But the eyes... how do we keep from having to deal with those clunky visors?

Well... we have Google glasses and Apple glasses and auto-focusing glasses and auto-tinting glasses so I don't think it's hard to believe even a near-future where the helmet is tight to the head (hearing via bone conduction) with enough "glass" to wrap around the head for peripheral vision and all that "glass" is high-tech to auto-protect the eyes and face against all the nasty photons in the universe.

In fact, something that looks a bit like the thermal suit from Val Kilmer's The Saint comes to mind.

enter image description here

  • $\begingroup$ This is super cool. Tis a shame my world doesn't have bioengineering tech like that ;p $\endgroup$ Nov 3, 2020 at 0:58
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    $\begingroup$ @SomewhereOutInSpace - the bioengineering isn't that necessary. Body-sock with helmet and catheters may not be quite as cool, but would still work, allowing full pressure inside the helmet without restricting movement of the tight-fitting body-sock. No bio-adaption necessary. $\endgroup$ Nov 3, 2020 at 18:01
  • $\begingroup$ @PaulSinclair Although I didn't mention it in my answer, it was that exact reasoning that led me to retract my VTC and post an answer. Why does my left big toe need oxygen? It's not like it's spending weeks, months, or years in the suit. It just needs heat and pressure to be happy. Balance both and that toe would be as happy in space as on a beach. $\endgroup$
    – JBH
    Nov 3, 2020 at 21:04

You answer your own question. To be able to space walk — or hard vacuum work — at the drop of a hat, the wearers suit needs to provide the identical environment as their every day habitat.

The means they need to advancement in material sciences, biology, chemistry, and applied thermodynamics to be able to maintain the proper gas mixture under varying levels of exertion while dissipating heat, and recycling transpiration (sweat and breath) of water with a portable power source with a modicum of weight.

Fortunately, they’d not be so tight bound to the boost cost of the suits weight cause, presumably, they live in space or its easy to get there.

Plus, working in space is tiring. kind of like swimming everywhere you go without the benefit of thick resistive water to push against. Suits might need mechanical assist to amplify strength and endurance, which puts further demands on power system for energy and heat management.


Pressurize your space ship with heliox instead of nitrogen/oxygen. Helium dissolves significantly less in the blood than nitrogen, and the decompression time necessary to get into a low-pressure suit should be practically nothing unless you're running your ship's internal pressure absurdly high.

Of course, this may complicate some of the things you might like to do with plants as they use nitrogen compounds in their metabolism...

Otherwise, as has been mentioned, run your ship on pure oxygen, but at low pressure. This is almost as safe as normal air as reactivity follows the rules about "partial pressure" so pure oxygen pressurized to 20% of one atmosphere reacts about the same way as 20% oxygen at one full atmosphere of pressure. There's only a relatively small difference due to the absence or presence of the thermal mass of the nitrogen.

  • $\begingroup$ Fire is not one of the things that only cares about the partial pressure of oxygen: without all those inert nitrogen molecules getting in the way, things will burn much more readily than in air. The heliox idea is potentially interesting, though. $\endgroup$ Nov 9, 2020 at 16:41
  • $\begingroup$ I did mention the thermal mass of nitrogen for a reason. The reaction itself does only care about the partial pressure, but it takes more energy to heat up the nitrogen along with the oxygen, so effects vary greatly depending on what you're burning and how the thermal mass of the fuel compares to the air. Note also that humans can breathe at a lower O2 pressure than lots of combustion can sustain itself at. Ideally you run your station at the lowest O2 pressure that's comfortable to keep fire risk to a minimum, regardless of gas mix. You only need like 1.5psi to match Denver IIRC. $\endgroup$
    – Perkins
    Nov 17, 2020 at 19:32

The main reason that current spacewalkers need so much preparation time for a spacewalk is that their spacesuits operate with a low pressure pure oxygen atmosphere while their spacecraft operate in an Earth normal oxygen/nitrogen mix. Going from one to the other takes time because time must be allowed for the nitrogen to flush out of the system.

The other solution is to operate the spacecraft in a low pressure pure oxygen atmosphere so that the acclimatisation time is eliminated. This is the approach used in by NASA for the Gemini, Apollo and Skylab missions. For Gemini the spacecraft was pressurised with pure oxygen at one atmosphere at launch, and the pressure bled off to 5 PSI after launch.

The plan was to do the same in Apollo, but an electrical fault caused a fire in the cabin during a test for the Apollo 1 mission and the pure oxygen environment resulted in a deadly fire which killed three astronauts. Thereafter, the cabin had an oxygen/nitrogen mix at launch at one atmosphere's pressure, transitioning to pure oxygen at 5 PSI after launch.


You take one of these beautiful 60's style glass bubbles, 2 meters diameter or maybe a little bit less. Put a chair inside, strap arms and fingers and legs in some kinds of movable armrest / legrest. Or forget the legs. Why legs. Maybe there are magnets or grappers on the feet to fix the vehicle to the station?

Outside you attach mechanical arms and legs to the glass bubble which you can steer with those armrests and legrests. Add a small propulsion thing at several positions. 360 degree view with various sensors splashed across some screens in front of the user. Supplies for 10 or 20 hours.

(https://i.stack.imgur.com/QBPb4.jpg)![2001 Space Odysee]

Never mind some automatics which prevent user fuck ups, unwanted collisions and the like. A ratio button: normal ratio translates your move 1:1 to outside actuator moves. Finer ratios allow to slow down outside actuator movements so you get better control for some detailed work.

With this, it's just like getting into a car. Get in, start it, close the dock door, move where you like. The control chair can be inside the station for simple tasks, or you use the in-vehicle-chair for the more complicated stuff.

I am even convinced that, with the broader sensor range and all the tools you could fit into those mechanical actuators, this thing would be better for the task than an actually human-shaped suit. Imagine an IR cam that directly shows some gas leakage, as an example.


It doesn't take hours to vent N2 from your body when going from 1 bar to .25 external pressure. Especially since the pressure inside your body is not going down to .25 bar.

Divers can manage far larger pressure swings within half an hour. At far higher absolute pressure, where the gas solubility is far higher. It simply doesn't take that long. And there are hundreds of thousands of divers around the world. They have a very good statistics on what is safe and what isn't.

Running a pressure suit at 1 bar is extremely cumbersome for the tenant, the modern ones are bad enough at 250mbar. Sorry, I don't believe in those exoskeleton sci-fi ideas. Not going to work, not with forseeable technology.

If you want to be able to go into space without even a ten minute waiting period, you could run your station at 3:1 N2:O2, 750 mbar abs. pressure, and your space suits at 1:2 N2:O2, 300mbar absolute.

There is a reason why the MIR and ISS were run at normal earth atmosphere (Skylab used 1:2 N2:O2, 340hPa), and it is not the fire hazard (pure oxygen atmosphere is a terrible idea under earth gravity, but not in microgravity, where there is no convection): Breathing at 250 mbar absolute pressure is far too easy, and in a pure O2 atmosphere, you don't need to breathe much. It's simply a matter of physical exercise. The astronauts would probably not even survive the descent if you kept them in a low pressure pure oxygen atmosphere for half a year.


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