# can ice crystals be molded into a structural shape in space

I know that water exposed to vacuum space first boils and then turn into vapor (sublimates) . Is it possible re use this vapor say inside a pressurized membrane, to mold it into a solid ice structure, if you put ice inside a thin membrane could you maintain it's particles no matter what state they are in (solid, gas, liquid), what sort of pressure would the membrane have to endure? and would water molecules retain it's radiation insulation properties when in different states. These are basically questions for a spaceship concept.

• Minor note, ice is the solid form of water. There are no vapor crystals, that would be small solid bits floating around. Vapor is the gas phase.
– Jim
May 6, 2015 at 15:38

My educated guess is that a large block of ice, delivered to space somehow, would last quite a while. If we assume it is in Earth orbit, the side facing the sun would sublimate (go directly from solid to gas) and dissipate. The rate of sublimination would depend on the insolation (power per unit area), which is about 400 $W/m^2$ and the absorption coefficient of the ice.

If we take a 1 $m^3$ block of ice, square on to the sun and assume 50% of incident radiation is used for sublimination, we would have about 200W available. If the ice is in equilibrium temperature with space (about -270 C) we have to first heat it to 0C and then melt it. That takes about 400J per gram. We have 200J per second so can subliminate about 2g of ice per second. At that rate, our ton of ice would last about 6 days (so not so long).

In deep space, say out in the Oort Cloud, where the insolation is milliwatts, it'd last a lot longer. This, by the way, is where comets usually live and they are mostly ice...

As a complete aside, Arthur C. Clarke in Songs of a Distant Earth, imagined a starship that uses a shield made of ice as it voyages through interstellar space.

• thank you for your answer. I didn't read distant earth, now I will. But what if our ice is inside a thin membrane? what would happen to the ice/vapor, what would happen to the membrane, would it be possible to contain it no matter what state water is in? I'm sorry for my lack of intellect, I am just an architect trying to understand so that maybe I can do something creative with what I learn. May 11, 2015 at 17:30
• IIRC, in SOADE, they sputter-coat the ice in a film of gold! The purpose of this is to increase the reflectance and so reduce the sublimination. Generally, though, if the ice melts, you've got a giant water-filled balloon. Guess you know what usually happens to those. (You might want to upvote my answer, btw :-) May 13, 2015 at 9:43