# Feasibility of super-fast airlock using Utility Fog

I've been trying to imagine a convenient future airlock for people on planets with little atmosphere (which is most of the bodies in the inner and outer solar system).

It feels like waiting 15-to-30 minutes each time you have to ingress or egress is a subtle, but substantial, pain.

Utility Fog, sometimes also called gray goo, is a metallic mesh made up of tiny (100 $$\mu m$$) grain-of-pollen shapes robots with multiple telescoping interlocking small arms. The robots as a network can change density and shape by telescoping arms in or out and letting go to grab a new partner. It was originally envisioned as a high-tech alternative to air bags.

My thought was that a super-fast airlock could do this during ingress :

1. An extremely dense (minimal micropore) layer of utility fog forms just inside the inside door
2. The utility fog expands, kind of like the gas inside of a piston, to fill the entire compartment.
3. The super-dense region of utility fog moves like the piston of an engine from the inside door to the outside door, automatically adjusting its shape to allow the people and objects to pass through and pressing no harder on surfaces than 1 atmosphere.
4. The inner door, which was vented, allows interior air to fill the gap behind the utility fog.

An entire airlock full of users passes through in seconds.

Is this feasible? Anything really important that I'm overlooking?

Some Assumptions-

• Best practices allow standardization between suit and habitat pressure.
• Future technology allows semi-rigid suits that do not need to be over pressurized prior to opening the airlock
• This question is focused at negligible atmosphere environments, and retaining most (not necessarily even all) of the hab atmosphere. Keeping toxic gasses out is not a concern.
• Dust and other contaminants are taken care of by another system, or not taken care of at all.
• Comments are not for extended discussion; this conversation has been moved to chat.
– L.Dutch
Apr 23, 2021 at 2:11

You don't have airlocks at all, your vehicles and things are normally outside, and left outside (in the equivalent of a shed), and your pressurized suits are attached to the outside wall of your base, waiting for your staff to climb into them, then the space is sealed behind them.

This is called a suitport.

The only use for an airlock is a life-or-death emergency, in which case you can do an emergency repressurization for the disabled crewmember (hopefully still in a standard pressure pressurized suit, otherwise they have bigger problems than the bends already), while any other crew can go back into the base the normal way via the suitport.

• This is a good idea, and what I've been using so far. However, the world I'm building this question in has at least thousands of people operating daily in this environment. As I'm using it, this starts to feel a bit clunky about "where's my suit"? Apr 19, 2021 at 21:33
• @JamesMcLellan You could come up with some creative ways to integrate a system like this with your habitat design. Maybe the people treat their suits like 'cars', where they have a 'garage' port attached to their living quarters, and then shared 'parking spots' anywhere else they need to 'dock' the suits. Each suit has some kind of personal 'key' that prevents other people from using your suit, and allows you to easily locate where you 'parked' your suit. Apr 20, 2021 at 2:42
• @JamesMcLellan Make the suit out of utility fog that forms around you as you step through the wall.
– rek
Apr 20, 2021 at 12:06
• – PTwr
Apr 20, 2021 at 20:20
• Actually the premise of this is that the EVA suits have the same pressure and breathing gas composition in them as the inside of your habitat. In which case there is absolutely no problem quickly pressurizing and depressurizing an airlock either, because the pressure stays the same inside the EVA suits. This system still has benefit in not wasting any precious breathing gas that would be vented out of the airlock when depressurizing. Apr 20, 2021 at 21:02

It's not a mechanical problem

Your premise is that conventional airlocks take 15 - 30 minutes, and that's fairly normal. Official documents (pg 101) mandate 30 minutes for the depressurisation operation after a 45min pre-breathing session, though they don't actually say how long the process physically takes to decompress the airlock.

The emergency procedure for quickly repressurising (pg 385) leads straight into treatment for the bends though, and some digging online suggests a crash-repressurisation period of only 45 seconds.
I really wouldn't want to be required to do it!

The upshot is that going from 1-bar to 0 in seconds is really really bad for human biology and your utility-fog approach in no way would protect users from decompression-sickness.

• The suits aren't hardsuits. they're flexible, and so whatever pressure is outside them affects their internal pressure. I'm pretty sure the station operates at less than 1-bar, but it's still well above the half-bar that is the minimum requirement for humans. Apr 19, 2021 at 14:13
• I’ll add it to the question, but I’m assuming suit technology has advanced sufficiently (and that there are regional standards as required) so that the pressure differential between inside of habitat and inside of suit is negligible. Good thing to keep in mind of. Thank you! Apr 19, 2021 at 15:26
• @Ruadhan you don't necessarily need hard suits. If the material is skin tight enough, it can maintain pressure. en.wikipedia.org/wiki/Mechanical_counterpressure_suit Apr 19, 2021 at 23:41
• Just went away and did the math. Official scuba-diving guidelines suggest 30 seconds for half a bar of pressure-differential. (I had to do a bunch of conversions, but basically half a bar is 72PSI, which is equivalent to 16 feet, and the guidelines say 30-feet per minute is your ascension rate) Which I guess interestingly means that assuming the suits are designed with some leeway you could definitely depressurise an airlock in under a minute with no ill effects. Apr 20, 2021 at 12:17
• @Ruadhan, there is no half-bar minimum; the EVA suit has ~0.2 bar (pure oxygen) only, and IIRC Apollo had the same throughout the flight. I haven't actually heard good argument why ISS includes the maybe 0.5 bar of nitrogen. Apr 20, 2021 at 21:24

My first thought is that you are grossly overlooking decompression sickness

Decompression sickness (DCS; also known as divers' disease, the bends, aerobullosis, or caisson disease) describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization. DCS most commonly refers to problems arising from underwater diving decompression (i.e., during ascent), but may be experienced in other depressurization events such as emerging from a caisson, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.

The original name for DCS was "caisson disease". This term was introduced in the 19th century, when caissons under pressure were used to keep water from flooding large engineering excavations below the water table, such as bridge supports and tunnels. Workers spending time in high ambient pressure conditions are at risk when they return to the lower pressure outside the caisson if the pressure is not reduced slowly. DCS was a major factor during construction of Eads Bridge, when 15 workers died from what was then a mysterious illness, and later during construction of the Brooklyn Bridge, where it incapacitated the project leader Washington Roebling.

Altitude DCS became a problem in the 1930s with the development of high-altitude balloon and aircraft flights but not as great a problem as AMS, which drove the development of pressurized cabins, which coincidentally controlled DCS. Commercial aircraft are now required to maintain the cabin at or below a pressure altitude of 2,400 m (7,900 ft.) even when flying above 12,000 m (39,000 ft.).

Generally, the higher the altitude the greater the risk of altitude DCS but there is no specific, maximum, safe altitude below which it never occurs. There are very few symptoms at or below 5,500 m

By quickly letting people out of the high pressure environment you are basically setting them up for getting DCS.

And I guess the sudden change in pressure won't do any good to boxes and sealed container, either. When I worked with a glove box one of the first things that was taught was to be gentle with changing the pressure in the airlock when transferring samples.

• The issue is much more related to the speed of the change than the extent of it. As long as your suit maintains enough pressure for your skin, and enough to breath, you're fine. But bear in mind that if the suit is half a bar, and the airlock is also half a bar, the astronaut is experiencing a full bar. Dropping half a bar in 45 seconds is probably pretty unpleasant! Apr 19, 2021 at 14:12
• @Ruadhan that depends on the design of the suit. It could maintain half a bar internal pressure. Apr 21, 2021 at 9:03

Since you are assuming that the suits share the same air pressure as the habitation environment, then Arthur C Clarke had one solution: The Kwiklock.

It's a spacesuit-sized, spacesuit-shaped airlock for large numbers of spacewalking shift workers building the first spinning-wheel space stations. He wrote about it in his conquest-of-space stories in the late 1940s/early 1950s.

Since there little empty volume when occupied, it minimizes the gas lost to space upon exit, and requires very little additional air upon entry. Each user takes only a few seconds to pass through.

It feels like waiting 15-to-30 minutes each time you have to ingress or egress is a subtle, but substantial, pain.

I think you're underestimating the amount of work that goes into working with hazardous environments, and the risk of dumping someone rapidly into that hazardous environment.

My related experience is with scuba diving. (I'm not very experienced, but hey.) It takes some time to kit up. Once you're kitted up, you cross-check your buddy's kit. You check all your gear works correctly. You keep checking stuff as you descend, and you check that your buddy is OK. Progressively pumping out air allows you to keep checking that your kit has pressure integrity as the pressure drops. An unobservable leak at 0.1atm differential will be a lot more observable at 0.5atm! You really don't want to rush this process, because it's literally the difference between life and death.

The suits also may not operate at 1atm. A lower pressure will still be breathable and reduce load on seals. If that's the case, there's also a decompression time involved which can't be skipped.

As for the time, NASA says that it takes 45 minutes to put on a space suit. Another 15 minutes to carry out checks as you decompress the airlock is perfectly reasonable in the context of it already having taken you that long.

I also foresee a major problem with the structural integrity of the suit with your Maxwell's demon barrier. Pressure suits are designed to have equal pressure all around them. Sweeping this barrier over the suit will give you a 1atm pressure differential on some parts of the suit and no pressure differential on other parts, making it balloon out. Normally it wouldn't be a problem because equal pressure everywhere makes the suit push out equally all round; but the barrier will give you point (or line) forces which aren't going to do it any good at all. Seals are also going to have problems when there's a pressure differential on one part and not on others.

In reality anyway, the time problem is only with egress and not ingress. The outer door will be closed during their time outside (for safety), but the airlock will remain evacuated. When they come back in, the airlock can be filled with air as fast as you like. The part that's slow is pumping the air out, not letting it back in again. Of course any place like this will have multiple airlocks, and there will be a cast-iron rule that as long as there are people outside, there are always enough airlocks to process them.

Airlocks can work must faster. The problem isn't the lock... it's the people. Our bodies need more time to adjust, or we get the bends.

<Warning: graphic video>

One solution: build the pressure adjustment into the space suits. We can do this now, but the suits are more like the old deep sea dive system. For your imagined world, you can allow that technology to advance for things to be more comfortable, flexible, and lighter. If you really want the small bots, perhaps you can use them inside the suit to handle internal pressure.

People put the suits on before leaving through the air lock. They set the suits to start depressurizing and then go outside immediately. The suit maintains the needed pressure, but also slowly and safely adjusts for the lower pressure in the new environment. When they ingress, people pass through the air lock again right away, as quickly as the lock is able to function, but they must leave their suit on. Instead of waiting in the lock, they set the suit to re-pressurize.

You can normalize seeing people moving about a station or building while still in a suit, not to provide breathing air but to adjust for the pressure from when they were outside. Then the suit beeps at them and sets a status light when it's safe to remove.

• Thanks for the answer. I wonder if maybe I'm missing something. If you look up at the suitport answer (#1 right now), the technology exists today to egress and ingress without ever changing your personal pressure. Considering that tech, is there some reason why bends is still a concern? (to the best of my knowledge hardsuits work, but maybe I've missed something) Apr 20, 2021 at 14:40
• @JamesMcLellan That system requires keeping the suit pressurized the entire time you're outside, such that any loss of integrity is a big deal. Even if the suit doesn't "pop", it's still pushing your air out very hard and fast. If you can lower the suit pressure while outside, a minor breach doesn't have to be catastrophic. The system also works such that those suits are the only things that can use the airlock. Fancy pressure-changing suits would be more flexible, allowing anything to use the lock. Apr 20, 2021 at 20:57
• The suits could even be a status symbol of sorts, where only a certain group of people are afforded the luxury of not having to wait for pressurization and there's a shady second-hand market etc. Apr 21, 2021 at 19:25

It sounds like your main goal is to imagine a world where leaving or entering the hab is as easy as opening the door to your house, and you're willing to jump wholly into the realm of nanobots/grey goo in order to make that happen...

So why not just do away with the whole conventional airlock business entirely, and instead construct a "door" out of nanobots where, as you walk through it, the bots wrap themselves around your body, preserving atmospheric pressure and providing mechanical counterpressure? Think about something like exocytosis!

I would think that, if the nanobots are technically sophisticated enough to meet all of the criteria you mentioned in your question, that they'd also be easily capable of linking together to form a "smart fabric" which reacts flexibly to user movements while maintaining the desired level of counterpressure. They don't necessarily need to be 100% airtight; if the colony has sufficient resources, they could tolerate a little leakage here and there.

You could imagine that people would need to grab a helmet and a backpack/PLSS off the shelf before they walk through this gooey portal, and that the nanobots simply serve as suit material, or you could go full-scale handwavium and have them automatically construct a full suit with transparent visor and mechanicals by the time the person has passed through the door. In either case, the person would simply need to walk back through the other direction to "doff" their suit and get back to whatever they need to be doing.

Try Plasma Windows (or in this case Doors) instead.

Plasma window - wikipedia

The technology would need to be refined of course but in a future SF setting with plenty of power available. Edit; In principal however what would be created is barrier that would hold in the atmosphere (or most of it) but be permeable to physical objects like space suits. The suits would have to be non-conductive (I think) and communication aerials etc insulated/inactive while passing through the plasma stream but that's just a turn off/turn on issue for the user - no comms while passing through the plasma.

Ideally you'd still have an airlock with two physical hatchways (inner and outer) but the exit procedure would be simple;

1. Enter airlock and close hatch (precautionary).
2. Activate outer hatch controls (which automatically activates the plasma window across the exit hatchway at the same time.)
3. Open outer hatch/exit the station or vessel while the plasma field contains the atmosphere. Close hatch - automatically switching off the plasma window.

Reverse procedure on return. You might consider reducing air pressure in the airlock (again as a precaution against an emergency 'blow outs' but you wouldn't have to go to vacuum.

The other cool thing (I think anyway) is that you could put these systems throughout a station or ship . So if a disaster depressurizes one or a series of compartments emergency power could give you permeable airlocks across any doorway they were fitted to that would activate automatically and instantly. Provided you have power of course.

• -1 for even not remotley considering the technology capabilities OP is talking about and making straight 90 turn for a different one Apr 20, 2021 at 7:11
• +1 a force field made of plasma and a force field of nanobots seems pretty close together on the tech tree, and the plasma window is a real thing that exists today... Apr 20, 2021 at 11:28
• Molb. I did consider the OP's technology. But since I had nothing to really contribute in terms of its feasibility or related engineering issues I decided to suggest an alternative which A) actually exists and B) might meet the OP's required parameters. Also as far as I am aware making alternative suggestions is generally encouraged on WBF. I'm sure if James M has a problem with my suggestion he'll let me know. Finally at least I tried to make a contribution. You've contributed what exactly by way of ideas?
– Mon
Apr 20, 2021 at 12:46
• Perhaps if you could elaborate more on this technology and list some cons and pros compared to the technology suggested by the OP your answer would be received better. Would you consider editing your answer? Apr 20, 2021 at 22:20

There are two reasons the airlocks at ISS take so long:

1. The internal atmosphere has approximately normal composition and pressure corresponding sea level pressure while the EVA suits have pure oxygen at just enough pressure to be safely breathable, because that's what you actually need and any extra inert gasses would just inflate it like a ball and make it harder to move in. However, body needs some time to release all that nitrogen. It is not much of a problem for recompression.

2. There is a whole lot other tasks to accomplish to ensure everything is working, because their lives depend on it.

But you don't really need the nitrogen. Apollo had pure oxygen throughout the flight. The discussion on space suggests that the main reasond for using Earth-like atmosphere are simpler take-off and landing—the transition from normal atmosphere to the pure oxygen is tricky and you can't just use pure oxygen before take-off, because you'd just burn like Apollo 1—and possibly cooling.

So when designing a permanent base on another body with little atmosphere, those reasons don't really apply. So have an oxygen-rich atmosphere in the station, use the same in the extra-station activity suits, and you can pressurize and depressurize the airlocks in a couple of seconds with no ill effects, because the pressure inside the suits won't be changing at all.