In science fiction, you often see people walking around on atmosphere-less planets and in space in spacesuits that look like armor, without the huge oxygen tanks that astronauts have to carry around today. So I’m wondering, can it ever be like that in reality? What’s the most volume efficient way to contain oxygen? Pressurized oxygen, or perhaps by extracting it from another substance like water, that is stored instead? Assuming that any technology to extract the oxygen from said substance isn’t a problem. What about liquid oxygen?
How much can you pressurize oxygen anyway? Could you technically pressurize any amount of oxygen into a tiny space, as long as you had the technology to pressurize and convert it to something usable inside the spacesuit? What are the limiting factors in this?
What’s preventing days worth of oxygen being pressurized into something the size of a matchstick box? (and it then being used?)
I think that they did that in order to have the characters walking around unencumbered.
In reality, I see problems. Oxygen takes up a lot less space if you condense it into a liquid. Unlike propane, though, it won’t stay that way without refrigeration, which is going to add to the stuff you have to carry, and burden you with a heat disposal problem in addition to the one you already have. If you could store oxygen in a solid material chemically ( Hydrogen storage - Wikipedia), you’d have something, but I don’t think you can store oxygen that way.
Rebreathers let you more efficiently use the oxygen you’ve got (and scrub out carbon dioxide), but don’t store extra ( Rebreather - Wikipedia ), so I don’t think they solve your problem, except maybe for short hauls.
The laws of physics. You can’t compress a liquid and all gasses become liquids at specific pressures and temperatures.
How about some sort of “rebreather” technology that converts exhaled CO2 back into breathable oxygen? That way you limit the amount of liquid O2 your astronauts have to carry around.
I got the “extract oxygen from water” thing from the ISS (international space station) their oxygen supply works by electrolyzing oxygen from water, which made me think that somehow water is a more volume/mass efficient “container” than pressured oxygen somehow, otherwise they could just use that.
Not even at really extreme pressure? It’s my understanding that this temperature simply rises the more pressurized it is, thus if it is pressurized enough it should be able to stay liquid at 0C, or however cold it is in space (without an atmosphere).
You also have the problem of exhaled gases going into a sealed space.
Current spacesuits scrub CO2 out into an umbilical cord (attached to vessel/ISS) or stored in cannisters. Unless you have a compression mechanism for the CO2, you still have a gas storage problem.
I suppose you can vent the CO2 outside the suit, but that may be a bit of a problem in environments where it will instantly freeze upon leaving the suit. Also a bit of an engineering challenge if you want the astronaut completely isolated from the local environment.
Liquids are usually pretty incompressible. Ignoring the engineering challenges of such a thing, a match stick sized box of liquid oxygen isn’t going to provide as much oxygen as you hope.
I suppose some combination of rebreather and highly compressed oxygen tank would do. Releasing the compressed oxygen would also help cool the spacesuit. It shouldn’t be hard to work that out in the universe where anti-gravity and warp drive are well established.
It’s “hard” science-fiction. I just want to know if its physically possible to have an oxygen supply of a few days in a spacesuit that isn’t bulky (oxygen container should be hardly noticeable), that can last days (with a rebreather).
Well, it’s going to depend on your rebreather technology. If you assume the membranes and absorbents, or whatever other technology is in use, is distributed throughout the suit, it might be feasible to get a couple of days. New technology that could seperate CO2 and leave all the oxygen behind might do it. But there’s a minimum oxygen consumption by a human being, so unless you can seperate the oxygen from CO2 you’ll be hard pressed to get there. I don’t know what the current state for water rebreathers is, but in the olden days those were pretty bulky units. I don’t know how dense oxygen can get in solid chemical compound, but I’d guess it’s not as good as gas compressed to nearly liquid state. And in the liquid state, IIRC, which I may not, it’s not much denser than the maximum pressure in gaseous form.
This is an especially difficult problem for female astronauts who are required to wear skin tight suits.
It’s the traditional sci-fi thing. Go back far enough and cover art would depict the guy wearing a bulky pressure suit, and the girl in a space bikini.
I was wondering about that. I know less than nothing about chemistry, but it seems unlikely the densest form of oxygen would be in a compound. The Russian’s emergency oxygen supply was special candles that were burned to produce oxygen. I forget the compound, but it’s been used in an old welding system. Great for long term storage I guess, but seems unlikely as most compact way to store oxygen.
That’s not necessarily true. My wife was on supplemental oxygen from a device that used liquid oxygen, and it had no refrigeration. She used it 24 hours a day, and it only had to be filled twice a day, from a 37 liter Dewar flask storage tank in our garage. There was no refrigeration apparatus on the storage tank either, and it was only refilled once a month.
It is true that if left indefinitely, the liquid oxygen will eventually boil away, but a Dewar flask can extend that to a very usable period.
If you had some way of extracting oxygen from the CO2 in some sort of rebreather setup, you could get by with very little additional oxygen.
Furthermore, if you were able to reprocess all human wastes (gases, liquids, solids) into their consituent elements, you could probably do away with supplemental oxygen altogether.
Electrolysis of carbon dioxide into carbon monoxide and oxygen has been demonstrated. It’s quite energy-hungry and requires some complex machinery and high temperatures, but if your story is assuming high-density power sources and miniaturization of the appropriate technology it won’t be too implausible. That gets you half of the oxygen back. Getting the other half back will be more difficult.
It is also possible to combine carbon dioxide with hydrogen to get methane and water. You can then split the water to get all of the oxygen back, and some of the hydrogen. There’s not much you can do about the hydrogen bound up in the methane, so you’re trading carrying an oxygen tank around for carrying a methane tank around.
Your best bet might be to assume a water tank, high-density power sources, and some really miniaturized catalytic and electrolysis cells. Split the water for oxygen for your main resupply. Scrub the carbon dioxide out of the suit air and combine it with the hydrogen from the water to get methane, which you vent, and more water, which goes back into the tank. While you’re at it, you can also condense some water out of the suit air from exhalation and perspiration. This won’t completely close the loop, but if you can assume the required technologies exist it will keep you going a while.
I think this is the way to go. Given sufficient energy sources and engineering, you could potentially have a very small machine that would just take waste (solid, liquid, exhalation), and recombine it into the necessary human inputs. The fundamental physical constraints on energy storage and chemical processing allow for much more compactness than hauling raw materials around and throwing away the waste, although obviously the engineering required to get there is substantial.
If we’re assuming sufficient technology to fit the power supply in a suit, we might as well also assume sufficient technology to recover all of the oxygen from carbon dioxide. And, for that matter, technology to recycle all the rest of the matter in the space suit, and if you stay out of combat, you could die of old age in there
Chemical oxygen generators are used already when space is at a premium. Personal breathing equipment for aircraft have O2 generators. They pack down into a box the size of a couple of volumes of an encyclopedia, provide O2 for about 20 minutes, and the vast majority of the space is taken by the hood itself. O2 generators are also used for supplemental oxygen for the passengers. The ISS uses O2 generators as a back up supply of oxygen for the astronauts, with one canister providing 24 hours of oxygen for one person. The downside to these things is the heat they generate.
There is a concept called respirocytes which are manmade, theoretical artificial red blood cells that exchange oxygen and carbon dioxide at 236x the efficiency of human red blood cells. Ray Kurzweil has said if you replaced your bloodstream with them you could go 4 hours without breathing.
So there is that as a potential method too.
I assume if/when devices like that are made their major impact will be on helping people who are victims of heart attack or stroke from avoiding organ damage before they can get proper medical care.