Author Topic: Could a cold sink on the moon work? (Read 13821 times)

dunwich · « **on:** 05/02/2023 05:39 pm »

Some parts of the moon are naturally in a permanent shadow. Resulting in temperatures of l25K-70K .

some equipment like quantum computers and the james webb telescope work at temperature of 50K.

Could a solar sail above the surface cool a region that is suffiently large to cool the underground to the single digit kelvins. Whilst you can place heat sinks deflecting the temperature of the device itself. SO even if your device produces heat the ambiet temperature stays low because the heat get's spread out?
(Because if you ignore the waist heat from the device itself I imagen it would be cheaper to simply do it i space not?)
Would the moon be a ideal body for that and would their be a use for a passively cooled region to a realistic cold temperature, would that temperature be close to 25K as measured naturale or below 10K given a big enough sail reflecting heat back into space.

Alternativly if you place the reflective sail at the equator and let it sag as a parabolic reflector could you focus all that sunlight into a central tower or a stirling engine that is connected with a conductor to the ground? (I imagen it wouldn't work during the lunar night)

whitelancer64 · « **Reply #1 on:** 05/02/2023 05:48 pm »

The coldest crater measured on the Moon is 26 K. You can't get less than that without active cooling. The reason is that heat from the Moon itself is constantly radiating out in all directions, including into the permanently shadowed craters.

For your other idea, it would be a lot easier to use a large amount of small, flat mirrors to reflect solar light to a central hot tower. This is already being done on Earth.

Proponent · « **Reply #2 on:** 05/02/2023 06:18 pm »

Being composed of largely of fine, dry particles, the moon's outermost layer is probably a poor conductor of heat. The story might be different if you could drill down to something rocky. Otherwise, the dark sky probably makes a better (radiative) heat sink than does the lunar surface.

Phil Stooke · « **Reply #3 on:** 05/02/2023 06:34 pm »

"Could a solar sail above the surface cool a region that is suffiently large to cool the underground to the single digit kelvins. "

How would this work? How does a solar sail cast a shadow on one spot long enough to cool anything significantly? You might have a huge sail and cast a shadow that drops temperatures by 200 K or something like that - during the day - but it's moving in orbit, it can't cool for long. If it's in a synchronous orbit - if such is possible at the Moon - the sun shines from a different direction all the time. If it's aligned with the sun vector, the moon rotates under it. You can't cast a shadow on the same spot for very long.

dunwich · « **Reply #4 on:** 05/02/2023 06:41 pm »

Quote from: Phil Stooke on 05/02/2023 06:34 pm

"Could a solar sail above the surface cool a region that is suffiently large to cool the underground to the single digit kelvins. "

How would this work? How does a solar sail cast a shadow on one spot long enough to cool anything significantly? You might have a huge sail and cast a shadow that drops temperatures by 200 K or something like that - during the day - but it's moving in orbit, it can't cool for long. If it's in a synchronous orbit - if such is possible at the Moon - the sun shines from a different direction all the time. If it's aligned with the sun vector, the moon rotates under it. You can't cast a shadow on the same spot for very long.

A solar shade material that is more used like a tarp (its fixed to the surface with the reflective side up)

edzieba · « **Reply #5 on:** 05/03/2023 06:45 am »

Quote from: Phil Stooke on 05/02/2023 06:34 pm

"Could a solar sail above the surface cool a region that is suffiently large to cool the underground to the single digit kelvins. "

How would this work? How does a solar sail cast a shadow on one spot long enough to cool anything significantly? You might have a huge sail and cast a shadow that drops temperatures by 200 K or something like that - during the day - but it's moving in orbit, it can't cool for long. If it's in a synchronous orbit - if such is possible at the Moon - the sun shines from a different direction all the time. If it's aligned with the sun vector, the moon rotates under it. You can't cast a shadow on the same spot for very long.

A steered statite might be able to handle it, but it would make more sense simply to mount the sunshade to the ground. A nice big aluminised mylar cylinder in a high/low latitude location (or angled) such that the Sun can never track inside the cylinder will chill down very effectively. A roll of plastic and some tent poles is logistically simpler, and more reliable, than launching a sunshade.

Vahe231991 · « **Reply #6 on:** 08/26/2023 10:25 pm »

With the Chandrayaan-3 lander having successfully landed on the Moon's south pole to begin investigating whether water is present in this region of this moon, if any water is detected at the lunar south pole, further analysis of the temperature of whatever water could be found is necessary before space colonists ever contemplate developing a cold sink on the moon.

dunwich · « **Reply #7 on:** 09/11/2023 06:05 pm »

Hello Vahe231991
thx for responding.
Chandrayaan sure is interesting no water so far and let's hope it will get out of it's slumber in 2 weeks time.
It is nice they discovered that the martian dust is a better insulator then tought (at least for the local region).

It is surprisingly hard to estimate how much water a mannend lunar program would need.
That said I know that the progress M 28M containend 420 kg of water. but I can't estimate how much of the ISS resupplies are water (by mass). I know some systems consume water like oxygen production, water reclaiment itself isn't 100% efficient and water will simply leak out, but how much?

Having decent thermal insulation is a good thing to know Let's hope the japanese SLIM will bring further discoveries.

Somewhat returning to cold sinks?
could it be used for in situ power generation?

We have seen blue alchemist produce a solar cell (prototype).
If we would have a large sheet covered somewhat over the surface, but make it dark it would start heating up during the day, it would also cast a shadow creating a cold trap, could electricity by won by that at least more easly then building the infrastructure to make solar panels?

(this would be a simplified concept),
I imagen having a heat absorbing sheet on top a (infrared) reflective sheet underneath and some sort of heat sink (perhaps a thermal conductive sheet) just below ground in the cold trap.
Then you connect the warm absorbing sheet with a inported sterling engine.
The temperature difference for the sunlid side would be 106°C, 379K to shaded side potentialy -183°C or 90K.
the heat transfer would generate energy and heat up the shaded heat sink. But then you simply occasionaly move the stirling engine towards a other sheet with cold trap.

Not the best energy source (it does not work during night time) but compared with solar cells?
(stirlings are roughly 40% efficient that is somewhat better then solar cells) It would take more math then I know to figure it out.

But it is potentialy a other usefull use for a cold trap

coupleriding · « **Reply #8 on:** 11/09/2023 12:39 am »

In comparison to the shaded side, which will be -183°C or 90K, the sunny side will have a temperature difference of 106°C or 379K. The hidden radiator will be heated by the process of heat transfer, which also produces energy. Simply transfer the stirring motor, once in a while, to a different plate using a cold trap. A huge piece of fabric covering a portion of the surface that is left in the dark will begin to heat up during the day and cast a shadow, which will result in a cold trap.