Some discussion around the existing question What is the largest naturally occurring body that could be hollowed and safely lived in? has lead me to post this question. I think the solution revolves around the strength of water ice in a vacuum, but I may be mistaken.

Assuming 100% pure water ice is used to create a hollow structure could it be pressurized to support human life suitable for a space station or transportation device (spaceship)? If yes, what is the largest structure that could be safely constructed?

There are of course many variables

  • The structure is 100% pure ice, insulating materials inside the structure are anchored to the sphere/structure without providing structural integrity
  • A naturally existing body may be hollowed
  • A structure may be created from pure water
  • A sphere is imagined but not required
  • At least half the radius of the structure must be hollow (no building caves on Europa)
  • Sublimation may be addressed without providing structural integrity
  • Spin to create gravity is desirable but not required
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    $\begingroup$ The hard sci-fi book "The Next Continent" wrote about lunar igloos near the moon's south pole. They argued it with physical principles and referenced some NASA architectures that used a similar method. Adhesion between blocks of ice was achieved by spraying water which then froze. I think that answers to the title of this question, but the full question may have broadened a little bit too much... $\endgroup$
    – AlanSE
    Mar 6, 2015 at 20:08
  • $\begingroup$ I was trying to keep the title simple, do you think it needs to be edited to more closely match the body of the question? $\endgroup$ Mar 6, 2015 at 20:19
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    $\begingroup$ Not sure what you mean by "Sublimation may be addressed without providing structural integrity" At 90k, ice in a vacuum starts sublimating at a good rate. I suppose with ice you could have a nice reflective surface, say a 90% albedo. To get a 90 k black body temp, 3 A.U. is sufficient. However the humans within would generate heat. $\endgroup$
    – HopDavid
    Mar 6, 2015 at 23:07
  • $\begingroup$ Are we assuming the inside to be directly connected to the outside, or would it be pressurized and/heated? $\endgroup$ Mar 7, 2015 at 14:06
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    $\begingroup$ My first glance Googling seems to indicate ice is a crumby material so far as tensile strength goes. But most ice balls aren't pure ices. There's often some metal, alumina, silica as well carbon and nitrogen compounds. There's science fiction where people just hollow out an asteroid and -- Voila! -- A living space! I don't think that's plausible. But building a hab from asteroidal materials is doable (in my opinion). Metals and materials for a supporting structure would need to be extracted and then the beams, mesh, etc., manufactured $\endgroup$
    – HopDavid
    Mar 10, 2015 at 17:13

1 Answer 1


Ice tensile strength is 0.7-3.1 MPa (100-450psi) and varies little with temperature. It decreases with increasing size due to the high Weibull modulus (which quantitates the variability of brittle materials). https://link.springer.com/article/10.1023/A:1021134128038#:~:text=The%20tensile%20strength%20of%20ice,relatively%20insensitive%20to%20these%20variables but this difficulty can be handled with ice composites.

100% ice strength is about half that of concrete. You have to launch concrete into orbit, but you can get water from asteroids. This is sounding pretty good.

The OP limits the proposal to “100% ice”. I think this is unfair. Ice composites like Pykrete https://en.wikipedia.org/wiki/Pykrete have about 4X the tensile strength of ice, significantly higher than concrete. Although Pykrete, by definition, uses sawdust, modern “hip” versions use hemp. All those greenhouses proposed for Mars…. I see possibilities for an export industry.

Refrigeration may be required to keep Pykrete frozen. But, with a microwave background temperature of 2.7*K I don’t think that would be a big challenge outside Venus orbit.

To answer the OP, YES. Position a water-rich asteroid or comet core using a solar powered steam rocket tug. Mine it for water using a reactor-powered heat-pipe probe. Mix water with solar greenhouse hemp and build a space habitat of your dreams.

  • $\begingroup$ Larry Niven proposed an interesting water-based construction technique in his Belter stories. everything2.com/title/Confinement+Asteroid "A hole was drilled down the axis of the asteroid and it was filled with plastic bags of water, then re-sealed. Jets were mounted to spin it on its axis. As it spun, solar mirrors heated it and the expanding water transformed the nickel-iron-composite, turning it into a bubble 12 miles long and 6 wide". $\endgroup$
    – PM 2Ring
    Nov 29, 2022 at 9:07

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