# Can various human-like aliens live together on a space station with a common atmosphere?

My idea is to build a universe with various alien species. There are dozens of different species and every species evolved differently on a different planet. The problem arises when they want to meet each other on space stations. It is very uncomfortable to wear an environmental space suit, which regulates your own atmosphere, at a bar or club during your visit. So it was decided to set the atmospheric conditions of the space stations to 'fit' most of the species. The big question is: Does this work (on a long visit/for the staff)?

Let me give you some further constraints:

• The temperature does not matter. There are cooler and hotter places, but the differences of those temperature is fairly low, like walking into an AC-cooled building. The aliens can deal with it.
• The aliens have a human-like respiratory sytem. They all breathe in oxygen and exhale carbon dioxide, but are used to different oxygen levels in the air at different atmospherical pressures.
• The rest of the atmosphere is non-toxic (and not very reactive). It consists mainly of nitrogen and some trace gases, like our air.
• The atmospheric pressure is fixed, so there is no decompression needed between visiting different section of a space station. There might be decompression required when visiting or leaving the space station.

The problem is that oxygen is toxic if the atmospheric pressure exceeds certain limits, like shown here:

The easiest solution is that every alien is required to wear a mask covering mouth and nose (like Bane in Batman, but more stylish), which regulates the amount of breathable oxygen to stay in the safe zone. If an alien species requires more oxygen at the given atmospheric pressure, ventilators in the mask accumulate more air volume per breath, extract the additional oxygen, expel the rest and thus enriche the oxygen level. For lower levels of oxygen the mask just recycles exhaled air.

The thing is how to deal with the pressure. Too low pressure causes blood to boil or cells to swell (like the accident of Joe Kittinger). Too high pressure can cause nitrogen narcosis, but might be prefered due to lower overall oxygen requirements. It would seem that mild symptoms of nitrogen narcosis start to appear above 2 bar, so a safe pressure would be around 1.5 - 2 bar, assumed that the internal structure of the space station can support that pressure against vacuum.

But what about long term effects (like weeks/months on humans) of high (around 1.5 - 2 bars) or low pressures? And what about the effects of increased oxygen levels on the human skin? It is the biggest organ and houses a very complex microbiome, which is (intentionally) not protected from higher oxygen levels.

Can aliens (or humans) live on such a space station or under such atmospheric conditions just wearing a mask instead of a full environmental space suite?

• Let's confirm a few points: 1. All species breathe oxygen, but require different partial pressures of it; 2. All species don't require more than trace levels of other gases for comfort, and at trace concentrations those gases are not toxic to any other species; 3. All species can be comfortable at one certain temperature level. Jul 16 '20 at 16:53
• Read Larry Niven's "Draco Tavern" stories. Jul 16 '20 at 17:44
• @Alexander 1) yes 2) have not thought about that in detail, thanks for pointing out...but let's just assume the mask also filters out hazardous amounts of other trace gases 3) yes Jul 16 '20 at 18:08
• Jul 16 '20 at 20:42

We can get a greater variety by adding another factor--this is a truly massive station with spin "gravity". The farther out on the station you go the higher the gravity--but also the higher the atmospheric pressure. You can have a common atmosphere even though the inner aliens and the outer aliens can't breathe each other's atmospheres.

If you want even more variety, consider oxygen concentrators. They're misnamed, they're really nitrogen concentrators (they concentrate the nitrogen out of the atmosphere, the "waste" can be 90% oxygen.) Your life support systems contain something of the sort on a large scale--extract nitrogen from the air feeding the habitat of the humans that like an 80/20 atmosphere and send it to the air feeding the habitat of the aliens that like a 90/10 mix. You have no air seals between the areas, it's just you keep separating it out. A human can walk into the 90/10 area (assuming the total pressure is Earth-like) with some difficulty.

• Thank you for that idea. When factoring in artificial gravity by rotation it would solve the pressure problem in a natural way. And with that life support system the other problem is also solved. Jul 27 '20 at 15:17

Low pressure. Supplemental O2 if you need it. And done.

https://www.boldmethod.com/learn-to-fly/aircraft-systems/oxygen-systems/?fb_comment_id=807177082667975_2232740406778295

On earth, people operate in unpressurized environments by using supplemental oxygen. The amount depends on how low the pressure is - lower pressure / higher altitude = need more O2 to meet metabolic needs.

Of course there needs to be enough O2 to prevent your blood from boiling. But low pressure and supplemental oxygen should be a solution for most of your aliens, and it sidesteps issues with high O2 toxicity for some individuals as well as things like N2 toxicity / CO2 toxicity etc.

It is not a big deal to walk around with a device that supplies supplemental O2. Many people do. There are portable battery powered concentrators that take it from the air and supply it.

Synthetic implants

This is one option than simply an external mask that fits over the entry of the respiratory systems. This could be temporary or long-term which would no doubt offer different types and for different purposes.

There could be external implants such as this:

Copyright: CBS All Access, CBS Interactive, Star Trek Discovery, 2017


This alien female has visible implants to help her breath because her homeworld has a much more toxic environment. The implants provide her with componants in the immediate area of her nose and mouth with each breath. Theses are permanent and graphed into her skin in at least two places. When forcibly removed it leave her unable to breathe and would damage her skin in the process.

Or

Internal Implants that could be installed into the chest (or anywhere) that helps deal with the pressure differences and would help attribute to adding or removing oxygen.

This would be both permanent which in considering you are also know how to maintain theses devices or short term which means they'd have to be in places that could be easily removable and not damaging to external or internal systems.

If everyone knows the risks in sharing a common atmosphere and the options of implants for keeping long-term in an unfamiliar atmosphere, then no one would be too worried until the technology is removed from the factor or environmental settled are out of control.