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I'm reading all kinds of things about mining water from the Permanently Shadowed Regions of the moon -- the bottoms of craters near the poles -- and I'm thinking Um, guys? It's 30 degrees Kelvin down there! That's 10 degrees colder than a bad night on Pluto!

What battery will function at that temperature? What material will not shatter? What lubricant works at thirty degrees from Absolute Zero?!? I have looked around for research and found nothing -- except an article about a bipedal robot in Ann Arbor (Go Blue!) that set a new record by walking for more than an hour at 8 below zero Fahrenheit before it died.

OK, terrific. Two hundred and twenty degrees to go.

Does anyone know of any research that has been done in this area? Any reason to believe we could ever do anything at all in such places?

michael_goulish
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    It's also a vacuum - many space vehicles have to actively get rid of internal heat. Where that is not enough, they can use radioisotope heaters (basically a lump of plutonium). How are these robots being powered in the first place? Likely RTGs. – IronEagle Nov 21 '20 at 20:30
  • Somewhat related: https://space.stackexchange.com/questions/30744/what-are-the-technical-challenges-in-building-a-titan-rover-that-didnt-need-hea – Steve Linton Nov 23 '20 at 09:48

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No, hold on. I don't believe I'm thinking about this the right way. IronEagle's comment helps. I'm thinking too much like an Earth guy.

If you go down into those PSRs, you are not in a 30 degree Kelvin environment. You are in vacuum. Vacuum does not have a temperature. In vacuum you can only lose heat by radiating it away, which is not at all like being immersed in cold air or water.

The only actual cold stuff down there is the regolith. Whatever parts of the robot come into contact with the regolith are the only parts that need to be engineered to not shatter in the cold.

And maybe you don't have to dig it up at all. Maybe you are only down there to build a dome to contain the water vapor that you are going to release with optical mining. The working machines are probably not even robots -- they are remotely operated devices being driven by humans who are just a few miles away on the crater rim -- up in the sunlight.

Maybe nothing will come into contact with the regolith except the vehicles' treads. I think we can figure out something that can survive thirty degrees Kelvin if all it has to do is give good traction and not break.

michael_goulish
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  • Good answer. If there are treads there will be thermal gradients and cycling with sunshine (sometimes) on the upper side of the tread and regolith on the lower, and of course the tread circles back not touching the surface. So materials need to take this into account in terms of repeated strain and thermal expansion/contraction. Also, on several of the cold solar system bodies there is concern that heating from astronaut boots or robotic parts will boil frozen gases in the surface and make the surface slippery when moving on an incline or even launch the spacecraft on very low gravity bodies. – uhoh Apr 19 '21 at 01:38