Possibility of airless spaceships being used for manned space combat?

Question

The setting I'm thinking of is in the not-so-distant future where humanity has become an interplanetary species using conventional propulsion. The solar system is largely colonized with human settlements going even as far as TNOs like Pluto.

Along with their settlements, humanity has brought warfare to interplanetary space. Hostile engagements between armed spaceships are similar to modern-day naval engagement and are resolved at a large distance using missiles.

Given the possibility of your ship being fired at having large amounts of air onboard is a significant liability. Air is combustible and escapes fast into vacuum through any significant fracture in the hull. It provides very little in terms of protection for the crew or structural integrity to the ship. Air's only real use onboard is that the human crew need it around them to breath, but that is not entirely the case in modern times and may not be the case in the future. In this setting there exists "liquid life support" and it is used extensively on military vessels built for combat. The crew areas of these warships are filled with a breathable liquid with density similar to water. The rest of the ship is hard vacuum. There is no air onboard.

You may wonder if this breathable water-like liquid is achievable and so do I but I'm pointing towards definitely. It's just a question of engineering either the liquid, of which chemicals with similar properties already exist (perfluorocarbons), mechanical artificial gills, or the crew to have actual biological gills.

Liquid life support provides the warship with a number of advantages. No air means no risk of fire or explosive decompression. The liquid shields the crew from radiation, absorbs more heat than air, mitigates the harmful effects of high-G acceleration and improves the ship's structural integrity.

Downsides include water being heavier than air, limited visibility and hearing inside a liquid medium. Technology could be used to mitigate the latter two and the first one is the reason this system is only used on warships built for brawling and not efficient hauling.

What additional downside could make this a really bad idea or downright impossible?

EDIT: forgot to mention that during normal spaceflight and during routine engagements, these ships have 0 G on board. There is no centrifugal gravity being generated, and gravity is only present during maneuvers. Water pressure would be maintained constant by a system of hydraulics.

Answer 1

Why not just have the crew in spacesuits? The suits could have a hard outer shell and double as escape capsules.

Answer 2

I'm afraid several of your assumptions are incorrect.

A liquid life support system means more pressure. As seen in the movie "The Abyss", it was used in high pressure EVAs under the ocean to prevent the person in the suit from being crushed. Having a higher density fluid, like water, you actually have more pressure (not less pressure) than air.

Also, this "liquid life support" would have to contain high levels of oxygen for the human body to function, so you're likely to have made the vessel more flammable, not less.

With the liquid being at a higher pressure, you've also made explosive decompression worse. Not only is the pressure from the inside more, but the pull on the humans inside the medium will be significantly more. There will be absolutely no chance of "holding onto a ladder/chair/control panel" to avoid being sucked out. With that much force on every square inch of a person pulling them out, even a "super soldier" wouldn't have the strength to keep themselves inside the ship.

Visibility wouldn't necessarily have to be limited, since there are seas on Earth where you can see for miles. A more dense atmosphere also makes things easier to hear, since the sound waves travel much more easily. You're likely to have too much sound, such as from engines, causing problems with too much noise.

Also, having a liquid life support would mean significantly more mass for the ship to accelerate, which means more fuel needed, more stress on the ship, and more time for the ship to make any turns.

As @PatJ mentioned, movement would be considerably hindered. Think about being in a swimming pool 24/7 while trying to do office work as well as reacting quickly to being fired upon. It's not just that it will be physically draining, but it will significantly hinder the crews ability to perform time critical tasks, such as throwing on any "force field" to protect a ship or returning missile fire.

There's also the cleanliness factor of several/many people being in this medium together. Think of the pool again, as well as simply walking past someone's flatulence. A liquid medium will make that odor stick around for a significantly longer period.

And for the same reason you don't like air, I think it's useful. It finds tiny imperfections and escapes through them. This is like having advance warning there's going to be a hull breach. A minor air leak is going to be found quickly and is easily patched. Think "Mission To Mars", where the air leaks were found quickly, but the fuel tanks were overlooked.

Again, with a higher density atmosphere, not only will sound propagate more, but so will concussions. This is how fishing with explosives work. The fish don't have to be hit with debris/fragments to die, they are killed by the concussion alone. What most movies don't show is that people can die simply from being too close to a large explosion.

As for absorbing more heat, that means you're going to have to heat more material to maintain a person's body temp, which means more fuel or more electricity. Without being it at body temp, the human body will be the heater, which will drain the crews energy reserves almost as fast as them having to walk across the Bridge.

A liquid medium might work to protect against high G forces in a small, confined area like a suit, but I have a feeling that it won't work as well in a larger space. That's not science, that's just a gut feeling (no pun intended) and some experience talking. An enclosed space restricts the fluid from moving as much, but a large open space would allow the fluid to move freely, so I don't think you'll be getting what you're wanting, without hand waving something.

So, TL;DR: you've unfortunately cause more problems than you are solving by making most of the problems you're trying to solve worse. Also, the problems you think will come up probably won't.

Answer 3

The advantage of air is that it can be compressed, in order to store it. Liquids are much more difficult to compress, and therefore would be much more difficult to store in order to make up for losses.

The other difference is that air is much less dense than are liquids.

Air locks would be reconfigured to, well, liquid locks. In order to egress from the spaceship for external repairs, cargo doors, etc. the egress lock would have to pump out the liquid. The lock would be replaced by - vacuum? Not sure how this would work, especially in zero gravity. How do liquids respond in a vacuum?

Water pressure increases the deeper you go, in diving. Air, not so much. If you have gravity, liquid pressure would be variable between the outside and deep interior of the ship. If you use rotation for creating gravity, you have an even bigger problem. The liquid would pool towards the furthest points from the spin axis.

If you have no gravity, then perhaps the liquid might be an advantage. You could swim through it.

Once the liquid starts to circulate, forming currents, it would drag everything with it. Since liquid is denser than air, the drag effect would be more pronounced. Like ocean currents. The ship would need some form of dampening for the currents. Simply moving a hand would cause objects much further away to move.

The liquid, being denser, would have a greater buoyancy factor than air. Things would 'float' in the liquid more than they would float in air. This would depend on the gravity, of course.

To revisit a previous point, air is compressible. So when one moves, the air immediately around you is compressed in the direction of travel. With a liquid, this compression would be negligible. The mechanical force would be applied over a greater distance. Movement would be harder.

If the liquid were denser than the humans, then they would constantly float in it, even under high gravity. It would be like astronauts training in deep pools to simulate movements in low gravity, no matter how strong the real gravity was.

The increased density, and thus mass, would greatly increase the inertia of the ship. Maneuvers would require a lot more propulsion energy, and would be slower. However, because of the increased density, the change in direction would be transferred to the humans more directly. They wouldn't have to hit a bulkhead before the change in direction was imparted to them.

Ever spin an uncooked egg, then stop the spinning, then let it go? It starts spinning again. The liquid interior has enough density to retain inertia, and then transfer it to the shell again. Ships spinning out of control would take a lot more to control the spinning. You can't just stop the ship from spinning, you have to stop the liquid contents from spinning. On the other hand, it would be harder to get the ship spinning in the first place.

Answer 4

Liquid life support provides the warship with a number of advantages. No air means no risk of fire or explosive decompression.

Your liquid would probably be flammable as it would probably be oxygen based to support human life. Also decompression would still be a problem but it wouldn't be explosive.

The liquid shields the crew from radiation, absorbs more heat than air, mitigates the harmful effects of high g acceleration and improves the ships structural intergrity.

Radiation shielding would be a slight plus but I don't know if the liquid would help with high acceleration more than air, pretty sure it can help a bit with deceleration but the actual acceleration would still have the same force on your body.

The structural integrity is not likely going to improve as the pressure of keeping the liquid inside the ship while accelerating would probably be much greater than keeping gas inside the ship.

My solution to not wanting air on a ship would be to keep humans inside specific rooms in cryosleep on ships. There should be very little a human need to do while being a ship like this and the travel time around the solar system with near future technology will still take years.

Answer 5

Soo many problems with this.

For a start your ship is gonna mass a metric fun-tonne more than it did. You need more powerful engines, you're slower and a hell of a lot less maneuverable, both of which are prime considerations for combat vessels.

Now you've got to make sure that all the equipment in the liquidified area still operates at 100% efficiency, does your liquid conduct electricity ? That's a whole new set of birthdays right there. To get conventional electronic equipment operating continuously "underwater" is gonna require them to be waterproofed, adding yet more mass to the ship. But assuming you can deal with all that, how do you change a hard drive or a graphics card underwater, reassemble the computer and get it to work without shorting out ??

Your airlocks, or liquidlocks, now require plumbing equipment instead of just vents.

How do you move the liquid around the cabin ? Air flows pretty easily but liquid needs pumps (heavy) which need maintenance and power.

How do you eat ? How do you cook food ? I'd love see how the bathrooms are plumbed :) And how do you clean up a trivial mess ? If my bag of chips bursts open on my desk it's no big deal to sweep them up and vacuum them away. Now try it underwater...

How would your crew members talk to each other ??

That was fun, thanks :)

Answer 6

Tl;dr - Bad idea, with serious health risks and repurcussions, plus additional equipment expense/risk. Both people and electronics operate better in air than in water.

1. Your skin will pretty much start disintegrating
2. You'd have to make every tool that the crew used water-tight or non-electrical, and wiring failures could be catastrophic.

I mean, it's possible to breathe liquids: https://biology.stackexchange.com/questions/23074/what-are-the-side-effects-of-long-term-liquid-breathing

However, this video reveals additional concerns, mostly with regard to skin condition. Human skin is designed to operate in air, not water, and many of its protective features will fail after extended exposure to liquid. For additional discomfort, just imagine the chafing. Even being a little sweaty can cause serious chafing for people... imagine being totally soaked 24-7.

Additionally, such a liquid environment would probably be a great conductor for electricity. You know how ridiculous it is for StarTrademark to show battle damage by having giant arcs of electricity injure/kill bridge crew? You've basically just made that reality - except now a single plug breaks its water-tight casing and you fry the entire mess hall. And now all your on-board electronics and crew tools have to be water-tight... the expense would be incredible.

Answer 7

The liquid will be confined to suits as many have explained, but I think even that is challenging. Imagine all the tedious process of going to the restrooms, eating, speaking and maneuvering in cramped places...

Answer 8

Possible see https://en.wikipedia.org/wiki/Liquid_breathing

Possible doesn't mean good idea.

Also something I read somewhere (may be fiction) indicated there was some psycho-physiological resistance to breathing fluid, and some people just couldn't do it.

One thing not noted so far that air is highly compressible, so when something goes BANG inside the ship the compression wave dissipates rather quickly. In water (or most fluids) not so much--they don't absorb ANYTHING they just transmit it.

Unless it's critical to the story, a MUCH Better idea is along the lines of a ship-suit that is designed to resist decompression that is "always" worn, and then when moving to "battle stations" one dons a helmet with a built in re-breather and a short term supply of oxygen, and a connection to air hoses. Then the ship decompresses internal spaces and then (possibly) floods them with pure nitrogen or pure helium (depending on how expensive the latter is in that world).

Having lots of fluid on board also dramatically increases your inertia and makes direction and speed changes take longer and/or cost more.

Answer 9

We all know space suits is suggested in mostly all sci-fi media around, but you have to face the fact that you still need oxygen for your space travel.

Given that your crew has space suits, there would be a time when they would exhaust their oxygen levels to the maximum, mostly during space fights, can you even imagine a ship firing head on at you, then realizing that you're out of oxygen?

Lets just say that your spacesuit comes with a oxygen generator, that would be so bulky It would only be usable under zero G.

I propose two things, one would be, remove the ship completely and use your suits for space combat, that way, you will not worry of any air or whatsoever for a ship in combat. Your ships will just become transports and your men will be the battle ships.

the second would be changing the crew itself, either biologically or anatomically.

Your main problem is oxygen which is required by your Human crew, and humans do need oxygen in order to live, just as you humans need your ship to fight. Having no oxygen negates that, I do agree that having a ship filled with water really makes matters worst, and having a crew under a spacesuit is only possible if your journey is just linear, having them their free will to fill up their space suits with oxygen if it requires them.

you may have your spacesuits bulky, then supersize everything.

or you may want to use Androids or Robots as replacement for your humans.

Since we are talking about Space wars, during those time I am presume that such technologies are possible.

1) Robots - you wont have any humans anymore, mechanized infantry would be the one to fight your battles on space, that way your ship will not require any oxygen of some sort.

2) Android - You first train your humans for space battle, then when they are ready for deployment, you transfer the organs that are required for battle. The lungs would also be removed due to its the one reason why your crew needs oxygen (and so is blood) you would be producing a part man, part machine type of soldier.

3) Genetic Mutation - You will still be a human, just mutated perhaps. Making the human lungs produce carbon dioxide and convert it to oxygen in one go. With this way, you retain your human form, but you don't require external oxygen to breath. This also keeps your ship "Air free".

You can also mate a human and an alien from an unknown planet which does not require oxygen to achieve a Genetically mutated soldier, but that would be another story.

Answer 10

One of the benefits of liquid would be a dampening of rotational effects (assuming you were at the centre of the rotation). However as pointed out in almost all the other answers conventional liquids have some significant issues: increased mass of ship, transmission of shock waves, some of the answers assume a liquid similar to water (such as boiling if the pressure drops to 0 psi) which would result in the water being expelled and the boiling would reduce visibility until the water froze as it boiled... sort of an interesting effect but certainly not a useful one.

Another possibility then is not a liquid but some form of exotic solid. There is considerable research in this area, however a much simpler answer which addresses some issues of acceleration, rotation is the use of suspended gyroscopes, which have the ability to be moved freely about) and are equipped with mechanically augmented suites (allowing you to work against high g forces).

How the proposed suites would work:

• Each crew member would have an unobstructed 3d view of space.
• The suites would be equipped with haptic feedback (you can feel the approach of multiple projectiles from different directions, other tactile features can let you know if another crew member is handling the projectile, the speed of the projectile and its distance, all of which without needing it to be in your visual field)
• the mechanical augmentation isn't to allow you to move freely (although at low g this may be the case) but rather to forcibly guide the limbs into positions which would create the least cardiovascular stress), the gyroscope is also working towards this end.
• visual rotation, and all other inputs are controlled though tactile interfaces which the computer interprets from pressure changes in the suit; that is, you don't have to physically move the suit to register the change but merely exerting your muscles against the force would be enough for the suit to acknowledge the input. The computer will calculate expected pressures within the suite and any variations detected are the will of the user. This is important because under very high g, actual movement might be virtually impossible.
• if these gyro units are allowed to move within the ship they can absorb some degree of shock (rather than if they were rigidly fixed), also if the rigging can allow them to move to the inside edge of the ships turn, it can reduce the g-forces experienced by the pilots, allowing even more aggressive turning maneuvers.
• a high degree of training would be required as there would be a significant difference between what people would perceive from tactile input vs what they perceive due to visual input.

I feel this sort of device would address the benefits of a liquid environment without its many failings. It may be possible that some future solid composite material which can behave like a liquid, may be able to perform all the above functions, including flowing in such a way as to move people into the inside edge of turns. Also simply because it is a solid does not mean it needs to have a density greater than most liquids as solids can assume porous structures. If such a nano-technology backed solid were available to your ships, they would be able to self heal and repair breaches, it could also react to explosive forces to absorb shock waves, both by changing its internal structure to dissipate shock away from undesired regions and by generating contra-shock waves, to cancel the force of shock in very narrow but critical regions. Also with such a complex material, you would have certain areas of the ship serving certain functions, but the underlying material would be more akin to stem-cells. That is any major system on the ship could be rebuilt, with time.

Answer 11

Another downside of liquid is mass. Water is about 800 times as dense as air. This results in a much more massive ship just for the water, then more extra mass to make it strong enough, then more extra mass for bigger engines to move it, then more extra mass for the fuel.

That said: A liquid filled acceleration couch make make it possible to for the crew to withstand greater accelerations. Consider a skin tight pressure suit with a helmut with inflatable air bags filling the space between it and your head; a couch that is gimbled so that you are always accelerating 'up'. You are nearly horizontal so that g's don't suck blood into your feet, and black you out. The couch is a loose membrane that will wrap around you in your suit. The liquid isn't water, but rather a silicone oil that is non conductive. If a couch is damaged, you have a mess to clean up, but you aren't going to short out circuits. The oil may have modified viscosity characteristics. Merit in having it like cornstarch and turning rigid under shock.

There are advantages to having most of the ship airless at least in combat. Air transmits shock waves quite well. Hit a ship hard (high speed rock, gamma burst, laser, bouquet of electrons at .999999c, whatever) and the shock wave can turn the air white hot. This is tough on anyone who needs to breathe.

High G combat would mean that during combat there would be no damage control parties. If you can't isolate, reroute, backup, etc from an acceleration console, you either have to ease off on maneuvers, or risk losing crew.

Answer 12

This was covered in "The Expanse"

During combat, the crew wear space suits because they know the ship will end up with holes in it.

If a ship gets shot while full of air, you have the immediate problem of no atmosphere for the crew but you also have the problem of the air escaping acting like a jet causing the ship to shoot off and/or spin in unknown directions like a balloon being let go.

Once combat is over, the crew can patch the holes and re-pressurize and then remove their suits.