Author Topic: Redirecting Sunlight on the Moon  (Read 3562 times)

Offline sanman

  • Senior Member
  • *****
  • Posts: 5974
  • Liked: 1312
  • Likes Given: 8
Redirecting Sunlight on the Moon
« on: 10/20/2018 05:49 am »
The lunar night is about 2 of our weeks in length, with temperatures plummeting as low as -173 C (some permanently shadowed areas are said to be a few tens of degrees above Absolute Zero). Certain elevated areas near the poles are said to be good candidates for lunar bases, because they are nearly permanently lit by sunlight.

What scope is there for redirecting sunlight on the Moon? Can benefit be obtained from this, perhaps for expanding the areas of settlement or operations? To what extent could such redirection of sunlight reduce the need for other energy sources such as nuclear reactors? Could redirection of sunlight be useful for mining of water from permanently shadowed craters?

What would be the best methods to redirect sunlight, for maximum practical benefit? Could redirection be done through orbital mirrors, or perhaps mirrors mounted on very tall towers?

Offline Lunadyne

  • Member
  • Posts: 56
  • EML-1. the crossroads of cislunar space
  • Liked: 50
  • Likes Given: 0
Re: Redirecting Sunlight on the Moon
« Reply #1 on: 10/20/2018 07:38 am »
Oh, this one is easy!

You're on the right path with going to the poles and thinking about towers.  It's been a while since I did the calculations, but IIRC, to permanently peek over the horizon you would need a tower three kilometers above the geodetic mean.  Given the weird, kinda egg-y shape of the Moon (bulgy on the Earth side, hunch on the backside, and a chunk out of the rear end) that's not so easy to calculate for any particular location, but the lunar poles are good real estate to start out with.

So how do you re-direct the sunlight you're perpetually peeking at?  Parabolic mirrors, which can serve industrial purposes, although I do have concerns about shining concentrated sunlight into <40°K everdark craters and the potentially explosive results.  You can use lightpipes to direct natural light into base facilities, especially underground, or work sites.

Outside of the everdark craters it is thought that there is a general low level of ambient light resulting from the low incidence angle of the incoming sunlight, and that temperatures will average around -40° (C or F; can't remember which ;)).  Regular mirrors on top of power towers (which should also be draped with solar cells) can help give area lighting.

This is all existing technology here on Earth.  Scientists have used parabolic mirrors to sinter regolith, and can achieve temps in excess of 10,000° (C or F; does it matter?  If it does I'm pretty sure that's F).  Lightpipes are used in modern 'green' construction.  Which means that NASA will probably come up with some kind of exotic, hyper-technical solution...

I'm not so big on orbiting objects around the Moon, as I want to give the radio astronomers on the far side as much of an advantage as possible before we start polluting their work.  I guess pole-sitting solar sails might be able to provide some functionality in regards to redirecting sunlight, but haven't really cogitated on it.  They're definitely perfect for comms into the everdark craters and the polar regions.

There's more on this topic in Schrunk, Cooper, Thangavelu and Sharpe's "The Moon:Resources, Future Development and Settlement", which is a good overview of the Moon development topics.  Although Eckart's "Lunar Base Handbook" remains one of my favorites.

Offline sanman

  • Senior Member
  • *****
  • Posts: 5974
  • Liked: 1312
  • Likes Given: 8
Re: Redirecting Sunlight on the Moon
« Reply #2 on: 10/21/2018 01:10 am »
You can use lightpipes to direct natural light into base facilities, especially underground, or work sites.

What advantage would light pipes have over electric transmission lines from solar arrays? Aren't light pipes perhaps an overly complicated solution?

Quote
Scientists have used parabolic mirrors to sinter regolith, and can achieve temps in excess of 10,000°

What's the purpose of trying to sinter regolith? Would this be for construction purposes, or oxygen extraction?

Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 1427
  • Liked: 727
  • Likes Given: 676
Re: Redirecting Sunlight on the Moon
« Reply #3 on: 10/21/2018 01:17 am »
Sintered regolith is good for roads and other construction.

Offline sanman

  • Senior Member
  • *****
  • Posts: 5974
  • Liked: 1312
  • Likes Given: 8
Re: Redirecting Sunlight on the Moon
« Reply #4 on: 10/21/2018 06:06 am »
Sintered regolith is good for roads and other construction.

Hmm, so would that kind of use of focused sunlight be best done directly on site on the ground, or could it be done from focused mirrors in orbit? At least with the latter you could be sintering nearly all the time, with less infringement from the lunar night. You might also be able to supply solar heating to keep equipment from freezing during the lunar night.

Offline TrevorMonty

Re: Redirecting Sunlight on the Moon
« Reply #5 on: 10/21/2018 08:23 am »
George Sowers(exULA) and School of Mines have been working on extraction methods. One of their preferred methods is to use inflatable dome (inflatable skin) with 2 attached rovers. Mirrors on crater rim would focus sunlight on dome on crater floor, the heated water is collected by rovers.
The sunlight also powers rovers and keeps them warm.

No information on how mirrors are deployed. My preferred method is lander with 3D printer and robotic arm printing a mast to which mirrors are attached, a mask of 10s metres should  be possible in low gravity. May need a few landers to give good coverage, the other mirror landers could direct sunlight on landers in shadow a few hours a day to help them survive lunar nite.

Checkout G Sowers twitter for more info.
« Last Edit: 10/21/2018 08:25 am by TrevorMonty »

Offline Eer

  • Full Member
  • ****
  • Posts: 624
  • Liked: 466
  • Likes Given: 913
Redirecting Sunlight on the Moon
« Reply #6 on: 10/21/2018 03:12 pm »
Clarifying ... that’s the Colorado School of Mines, yes? Appears that’s where George Sowers is at these days.
« Last Edit: 10/21/2018 03:13 pm by Eer »
From "The Rhetoric of Interstellar Flight", by Paul Gilster, March 10, 2011: We’ll build a future in space one dogged step at a time, and when asked how long humanity will struggle before reaching the stars, we’ll respond, “As long as it takes.”

Offline Coastal Ron

  • Senior Member
  • *****
  • Posts: 8860
  • I live... along the coast
  • Liked: 10199
  • Likes Given: 11929
Re: Redirecting Sunlight on the Moon
« Reply #7 on: 10/21/2018 03:34 pm »
Mirrors on crater rim would focus sunlight on dome on crater floor, the heated water is collected by rovers.
The sunlight also powers rovers and keeps them warm.

That certainly simplifies the energy issue, since mirrors are pretty simple tech compared to nuclear and other high-power energy systems.

Quote
No information on how mirrors are deployed. My preferred method is lander with 3D printer and robotic arm printing a mast to which mirrors are attached, a mask of 10s metres should  be possible in low gravity.

The Moon is not that far away that you can't ship in the fully-built masts and assemble on-site. Hauling a 3D printer to do some short-term work wouldn't make sense, plus the assumption at that point in time is that if you need all that water then there must be a robust transportation system in place to use it - so use it to set up operations.

Quote
Checkout G Sowers twitter for more info.

You didn't add the link...   :o
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Lunadyne

  • Member
  • Posts: 56
  • EML-1. the crossroads of cislunar space
  • Liked: 50
  • Likes Given: 0
Re: Redirecting Sunlight on the Moon
« Reply #8 on: 10/21/2018 10:33 pm »
Quote
What advantage would light pipes have over electric transmission lines from solar arrays?

Simplicity is one advantage.  Electric transmission lines would require equipment to convert sunlight into electricity and condition that electricity, the lines themselves, as well as equipment to re-convert that electricity back into visible light.  Light pipes are shiny metal tubes that direct raw sunlight.  There's some basic info at wikipedia: https://en.wikipedia.org/wiki/Light_tube

Quote
What's the purpose of trying to sinter regolith?  Would this be for construction purposes, or oxygen extraction?

Yes.  The point is that through the use of parabolic mirrors one can redirect (the original question) and focus sunlight to create high temperatures.  These high temperatures can be used for industrial purposes, including sintering materials for construction purposes (q.v. cinder blocks: https://en.wikipedia.org/wiki/Concrete_masonry_unit).  These high temperatures can also be used for pyrolitic oxygen extraction techniques.  And a bunch of other things as well.

Quote
would that kind of use of focused sunlight be best done directly on site on the ground, or could it be done from focused mirrors in orbit?

If you're at the Lunar poles, then tower-mounted mirrors should allow for near-permanent operations.

Quote
At least with the latter [in orbit] you could be sintering nearly all the time, with less infringement from the lunar night.

I'm curious as to how you envision this happening.  The lunar equivalent of geosynchronous orbit (selenesynchronous?) is at Earth distance.  So unless you're talking about a train of satellites that allow for mirrors to always be above the horizon, I'm not sure how orbiting mirrors would be an advantage.  Especially given the weird nature of the few stable lunar orbits; essentially long molniyas where you spend most of your time way out away from the Moon.  So you'd need tracking capability built into either the orbital platform or the ground facility or both.  I'm just not seeing it.

Quote
You might also be able to supply solar heating to keep equipment from freezing during the lunar night.

Things like lunar wadis (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120008795.pdf) have also been proposed to the same ends.

Quote
Hauling a 3D printer to do some short-term work wouldn't make sense

I tend to agree if it is specifucally a tower-pieces-forming 3D printer, but if it can serve more general purposes then a 3D printer is going to find lots of use on the Moon.  After all, how do you think they're going to get the parts for a vacuum still?

In the initial stages of lunar development the key strategy is going to be low-tech.  Simple machines, simple process, stuff that can be fixed or rigged relatively simply.  Things like slusher buckets for collecting regolith (basically ropes and pulleys), mirrors for focusing sunlight, pits for creating cold traps, thermocouples in the everdark craters, and other simple applications of technology that don't need to wait for a fix from Earth.

Offline TrevorMonty

Re: Redirecting Sunlight on the Moon
« Reply #9 on: 10/22/2018 09:15 am »
In regards to 3ad printing masts, see Tethers Unlimited and Made In Space both companies have demonstrated this. The alternative is trying to stack sections from 10s meters of boom on small lander (100-200kg).


Offline Nomadd

  • Senior Member
  • *****
  • Posts: 8840
  • Lower 48
  • Liked: 60430
  • Likes Given: 1305
Re: Redirecting Sunlight on the Moon
« Reply #10 on: 10/22/2018 09:21 am »
 There's Earth/Moon L1, but it might be too unstable for large, flimsy structures.
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
Re: Redirecting Sunlight on the Moon
« Reply #11 on: 10/22/2018 09:48 am »
Quote
What advantage would light pipes have over electric transmission lines from solar arrays?

Simplicity is one advantage.  Electric transmission lines would require equipment to convert sunlight into electricity and condition that electricity, the lines themselves, as well as equipment to re-convert that electricity back into visible light.  Light pipes are shiny metal tubes that direct raw sunlight.  There's some basic info at wikipedia: https://en.wikipedia.org/wiki/Light_tube

Over short distances.

Quote from: wikipedia
Light transmission efficiency is greatest if the tube is short and straight. In longer, angled, or flexible tubes, part of the light intensity is lost. To minimize losses, a high reflectivity of the tube lining is crucial; manufacturers claim reflectivities of their materials, in the visible range, of up to almost 99.5 percent
This means that if the light bounces a hundred and fifty times, you've lost half of it.

Geometry means that as the sun is half a degree wide in the sky, you can get at most half the brightness of the sun per unit area (concentrating mirrors do not help) after 15000 times the tubes length. (the light of a source with the tube pointed at it will bounce on average once every hundred lengths for a straight tube for a source the diameter of the sun).
You cannot improve this with any systems of lenses or mirrors due to conservation of etendu.
Wikipedia has a somewhat confusing page on this.

To put numbers on this, a 1m diameter tube can move 500W of light or so 15km.

This also means you cannot relay light with mirrors without the mirrors growing a lot.
If you have a 10m mirror, the absolute hard minimum spot it can create at a distance is 10m. It's not as good as this.
If you shine a beam from a 10m mirror 10km, due to the finite size of the sun, and then want to reflect it, you need a mirror 10m+sin(0.5 degrees)*10000m, or 100m wide, as the beam at that point is 100m wide.

Any system of light pipes or mirrors doesn't get round this, this is why we don't see light pipes more commonly - the losses are massive in real systems for solar input. Notice that there is an obvious engineering reason why you'd make a solar guide light pipe 5cm in diameter, not 50. That it's 50, with all of the structural problems is due to the above.

Offline TrevorMonty

Re: Redirecting Sunlight on the Moon
« Reply #12 on: 10/22/2018 01:27 pm »
For redirecting light from orbit, lasers work better. Solar to electricity to laser to concentrated light on lunar surface.

There is good FISO presentration on this,
http://fiso.spiritastro.net/telecon13-15/Schier_10-14-15/

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1