Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Underground Mars Habitat?

This site may earn commission on affiliate links.

Skotty

2014 S P85 | 2023 F-150L
Jun 27, 2013
2,685
2,255
Kansas City, MO
So, I was playing around with some calculations, in particular air pressure calculations. If Mars has a very deep molten core, and given that it's pretty cold there, then it's arguable that you could dig to some really deep depths with boring machines. Pressure should increase as you go down, just like it decreases as you go up. So could you dig deep enough to reach a depth where the atmospheric pressure would be suitable to human survival (assuming the temperature doesn't get too high and you have a breathing system)?

The height on Earth where supplemental Oxygen is needed is generally considered to be around 26,000 feet. I put this into an atmospheric calculator and it came out at about 5 psi (down from 14.7 at see level). I then played with the calculator to see how deep you would need to go to reach 5 psi on Mars starting from surface level pressure of 0.095 psi (assuming the calculator still reflects close to reality on such a calculation). Assuming I did this all correctly, you would reach 5 psi on Mars at a depth of about 150K feet, which is about 28 miles. Open question is what would the temperature be at this depth? And what would the material at this depth be? And will using the calculator in this manner, something it was probably not intended for, actually provide a close to realistic result?

Regardless of these questions, it seems at least viable for examination whether or not you could create a reasonable habitat by digging deep into the depths of Mars. A cave system at the right depth would provide increased pressure, increased temperature, and increased protection from radiation.
 
So, I was playing around with some calculations, in particular air pressure calculations. If Mars has a very deep molten core, and given that it's pretty cold there, then it's arguable that you could dig to some really deep depths with boring machines. Pressure should increase as you go down, just like it decreases as you go up. So could you dig deep enough to reach a depth where the atmospheric pressure would be suitable to human survival (assuming the temperature doesn't get too high and you have a breathing system)?

The height on Earth where supplemental Oxygen is needed is generally considered to be around 26,000 feet. I put this into an atmospheric calculator and it came out at about 5 psi (down from 14.7 at see level). I then played with the calculator to see how deep you would need to go to reach 5 psi on Mars starting from surface level pressure of 0.095 psi (assuming the calculator still reflects close to reality on such a calculation). Assuming I did this all correctly, you would reach 5 psi on Mars at a depth of about 150K feet, which is about 28 miles. Open question is what would the temperature be at this depth? And what would the material at this depth be? And will using the calculator in this manner, something it was probably not intended for, actually provide a close to realistic result?

Regardless of these questions, it seems at least viable for examination whether or not you could create a reasonable habitat by digging deep into the depths of Mars. A cave system at the right depth would provide increased pressure, increased temperature, and increased protection from radiation.
150k feet deep cave system. I like big thinking :)
 
Yup, To get to that level of pressure, because of lower gravity you may have to go deeper.
Good point. I found an alternate calculator that was intended for interplanetary and I also looked for more information on what the lower pressure limit is for humans to live comfortably (with breathing support), as my prior 5 psi baseline was just a rough guess based on when humans need supplemental Oxygen on Earth. I found information suggesting humans can live comfortably at about 1/5 normal Earth atmospheric pressure with breathing support, which should be about 3 psi. Recalculated for Mars gravity and assuming 3 psi is a viable pressure, that put the depth at 230K feet below surface level, or about 43 miles. That doesn't sound nearly as good as 28 miles, but still might be doable.
 
Good point. I found an alternate calculator that was intended for interplanetary and I also looked for more information on what the lower pressure limit is for humans to live comfortably (with breathing support), as my prior 5 psi baseline was just a rough guess based on when humans need supplemental Oxygen on Earth. I found information suggesting humans can live comfortably at about 1/5 normal Earth atmospheric pressure with breathing support, which should be about 3 psi. Recalculated for Mars gravity and assuming 3 psi is a viable pressure, that put the depth at 230K feet below surface level, or about 43 miles. That doesn't sound nearly as good as 28 miles, but still might be doable.
When we start talking about miles underground, it's all big in my book.

As a point of comparison, and some incremental information about drilling deep into the Earth:

44k feet or about 8 miles? I expect that the heat / pressure / seismic activity they talk about here that constrains first human ability to survive at these depths in a mine, and then for the equipment to continue to function, will be less restrictive on Mars.

And then a better article explaining that the infographic etc.. is false:

The gist being that you can't add horizontal distance to vertical distance to get to depth of well. Still an impressive well that first one, but there are others that are deeper vertically. Deepwater Horizon shows up on the list :)
 
Last edited:
Agreed.

Underground makes sense for sure, but pressure really isn't the driving variable--its radiation. Once you can get down low enough for have a comfortable level of radiation protection, the technology required to maintain habitable pressure its pretty basic.
Can the martian rock contain pressure? If so, a shallow cave (could still be hundreds of feet deep, so shallow as compared to miles) with a redundant pressure hatch would probably make more sense.

I guess my primary concern, if I was to be a Martian myself, would to have a habitat that I don't fear is always one small crack away from causing everyone to die in short order, so you can rest and sleep easy when off duty from any above ground work. Pressure would be my primary concern, as a sudden loss of pressure will probably kill faster than anything else. Most other stuff there will be time to try to fix if it goes wrong.
 
Can the martian rock contain pressure? If so, a shallow cave (could still be hundreds of feet deep, so shallow as compared to miles) with a redundant pressure hatch would probably make more sense.

Given that we humans were designed to operate at ~1atm, especially for long periods of time, it is a near certainty that any mars habitat will have a similar environment. Good news is that a pretty minimal enclosure can easily contain 15psi of pressure (canvas, sheet metal, etc.). If the rock walls of an underground habitat are too porous, the chamber can be lined with something similar.

Yes, there would be airlocks for an underground habitat to ensure the [relative] safety of the team, but any martian habitat would have them given the need to control atmospheric concentration within the habitable spaces, even one that's way below the surface

FWIW, ISS is a great case study here--unlike the ~5psi vessels of space past, it maintains ~1atm of pressure and still can pretty safely work around small leaks.
 
An interesting idea I remember hearing about is a "waterlock": a U-shaped tunnel that goes _down_ from the pressurized underground habitat, then sideways, then up to the surface, all filled with water, which astronauts would swim through (while spacesuited) to get to and from the surface. Conveniently washes off the Mars dust along the way, and balances/maintains the habitat pressure through gravity, rather than using a traditional airlock.

Such a system could easily be prototyped and tested on Earth by making a really large rigid straw (say 2m diameter, 20m long) sealed at one end, immersing it in water to flood it, then lifting the sealed end ~15m out of the water. The water will rise up ~10m above "sea level" inside the tube through vacuum pressure, and the top ~5m of the tube will be in near-vacuum. Just don't try to swim up it without a spacesuit!
 
  • Informative
Reactions: adiggs