[ExI] The Moon's Cold Embrace

Keith Henson hkeithhenson at gmail.com
Thu Aug 13 17:45:38 UTC 2020

Rafal Smigrodzki <rafal.smigrodzki at gmail.com> wrote:

On Wed, Aug 12, 2020 at 2:58 PM Keith Henson via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

> Rafal Smigrodzki <rafal.smigrodzki at gmail.com> wrote:
> ###That
> should be easy. Of course you would also need energy storage for the lunar
> nights,
> And how are you going to do that?  Import power walls?
### Molten salt storage driving steam generators?

The salts used on earth include nitrogen.  There is no nitrogen on the moon.

There may be a suitable salt for such storage available but I have
never heard of one.

### Nuclear generators on the
surface, with immediate heat rejection to space and energy transmission to
underground living areas?

The reactor would have to come from the earth.  Same with the steam turbines.

Later it should be possible to mine regolith for the metals in it.
But the regolith is so poor in free metals that some people think the
wear on the mining machines will be more than the metal recovered.

> ### but the area of solar cells needed to harvest this energy (at 1.36
> kW/sq.m) would not be insanely large.
> 5 x for typical solar cell efficiency, times 3 x for storage and
> losses, so it is a considerable area.

### Well, initially surface availability would not be a limiting factor.
The important question would be, how many hours of robotic work would it
take to build the infrastructure needed to support one person.

It's more complicated.  There is a diseconomy of scale for solar
plants and waste heat radiators.  Explained page 6 here:
https://space.nss.org/wp-content/uploads/L5-News-1979-07.pdf  for
solar panels, the mass of the conductors starts to dominate.

### If the ROI
is very low, the doubling time from the initial technology seed would be
too long to make it viable.

When you mention ROI, then you must have a profit model in mind for
what lunar settlers are doing.  Building condos or what?

> ### Yes, maintaining greenhouse
> illumination at night would warm up the greenhouse but active radiative
> cooling at night would be pretty effective.
> It would be.  But getting rid of waste heat is more a daytime problem.
> Not hard to do, costly in materials.

### If you are dug in, you can defer heat rejection until the night comes.
With enough mass between you and the surface you can even out the diurnal

You have to get the heat in and out.  What are you proposing for the
heat transfer fluid?  Oxygen from lunar rock or water is often
considered but it causes a serious fire hazard

> ### Being surrounded by a large mass and having access to practically
> unlimited
> amounts of mass to construct a settlement on the Moon is a big advantage
> over orbital habitats.
> For humans and the industrial process we use, it's a seriously wrong
> selection of elements.  Some students were once given a stack of
> high-temperature fire bricks as regolith simulant.  No carbon, no
> chlorine, no lithium.  The volatiles were all cooked out.  The lunar
> poles, which humans have not yet sampled, might have a better mix
> including water

### How deep do you need to dig to get what you need?

No idea.  Deep as you want and you will still not get carbon on the
vast majority of the lunar surface.  You *might* get a little carbon
from the poles.

###, even if the Moon is not the best source of building materials, it
still beats empty space, where orbitals would have to be built out of 100%
imported materials.

Al Globus thinks a LEO habitat can be constructed for a tiny fraction
of a moon settlement.  I have the same objection, what are they doing
there?  Al's concept of them living in orbit and telecommuting to
earth strikes me as unlikely.

> ### If you need to radiate heat, you just build a bigger
> radiator farm on the surface and run it all night long.
> Storing cold for two weeks takes lots and lots of mass.  And not just
> mass, but fluid to run through it and you don't want leaks.

### Yes, this makes things more expensive. Finding enough water on the Moon
would make it much cheaper.

You still need pipes, lots and lots of pipes.  Import or build a pipe
factory?  What do you make them from?  How much mass for the pipe
> >
> > Free space O"Neill type colonies are a lot less difficult with respect
> > to energy (light) for plants and heat sinks.
> >
> ### How so? The solar constant is the same on the Moon and in orbit.
> For most of the moon, the solar constant is zero for two weeks as a time.

### Conservatively you need 100 m2 of hydroponic surface with 40 W/m2
illumination per person,

A maze field on earth has a peak illumination of about 1 kW/m^2.  Some
plants will grow at 40 W/m^2, but I don't think humans eat any of

### so 4 kW during the night but running at a 12 hour
cycle so 2 kW per person during lunar night to keep your plants alive. This
is not a lot. Having only half the solar energy available would about
triple the amount of photovoltaics needed per person compared to an orbital
habitat, yes, but as I said, having all that lunar mass around you would
more than make up for that in many ways.


> ### Heat sinks are heavy, brittle,
> Why should a heat sink be brittle?  I have been involved with design
> studies since 1977 and that was never a consideration.  The most
> recent ones for power satellites are around a kg/kW.  They are tapered
> plastic tubes filled with low pressure condensing steam at 20 deg C
> and 2.4 kPa.  They depend on zero-g and would not work on the lunar
> surface.

### Good to know! Now, has there any work been done on heat sinks adapted
to lunar gravity?

No.  This kind of radiator depends on the droplets staying entrained
in the steam.  A lunar version would have to cope with water running
down to the low point inside the tubes.

### Is there a reason why such heat sinks would be in
principle less efficient than zero-g ones?

This kind of radiator will not work at all in any gravity field.

> ### Maybe you could mention the problems that don't have recognized
> solutions.
> The worst problem is why?  Why are people needed on the moon at all?

### Why not? If an affluent person can afford the trip, many will. I would,
if the social situation was right.


> None of this is impossible, just expensive.  ISS costs $100 B.  A
> minimal 100 person moon colony might cost one or two trillion.

### Not if we have a 50 ton 90%-self-replicating technology delivered at

I would like to see a proposal for this device even at the block diagram.

The best proposals I know about are $100/lg to LEO.  There is a large
multiplier to put cargo on the lunar surface, perhaps x 40 over LEO.

### Sure, using NASA-level inefficiency would make the whole endeavor
completely useless but I am talking about orders of magnitude improvements
in launch and build efficiency that should be possible with conceivable

I agree if you are talking about nanotechnology. If you are talking
nanotech, landing a coke can sized package is enough to industrialize
the moon.  But this side of the singularity, I don't think it is in
the cards.

> The next worse problem is radiation.  There are solutions, but it is
> not obvious that people can live underground

### People definitely can live underground, deep enough to take care of
cosmic radiation.

Can you think of an example where people live underground for years?
I don't know of any.  Even being inside and able to look out windows
causes serious mental problems for a lot of people if they do it too


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