"But if you are in a lava tube, you might not need much of a heat
source, your problem
is going to be radiating your excess heat out."

You keep ignoring how cold it is there, and how vast these lava tubes
can be. Even assuming you did need some kind of heat rejection, you
have the planet's own surface into which it can be conducted. You
can't do that on a spacecraft.

-michael turner

On Jun 29, 11:31 am, Alain Fournier wrote:
Michael Turner wrote:
Rebooting this discussion:

Let me suggest that the question be turned on its head: given the
likelihood that survival modes on both the Moon and Mars would be very
similar, what technologies would be location-unique?

I think these technologies will mostly be resource-determined, but
with some exceptions. Would you consider "proximity to the Earth" a
"resource"? Well, in a way: close proximity opens up much vaster
*human* resources. Certain operations might be practical to
teleoperate from Earth, in the case of the Moon, that would definitely
NOT be candidates for terrestrial teleoperation in the case of Mars.
However, in general, by "resource", assume that I mean immediately
available minerals, gases, energy sources, etc.

Examples:

Mars lacks:
- strong sunlight
- high daytime temperatures

The Moon is significantly lacking in:
- carbon (CO2 is most of Mars' atmosphere)
- nitrogen (N2 is around 3% of Mars' atmosphere)

Both are problematic for water supply, but Mars has ice caps, at
least.

I think the easiest supply of water for a colony on Mars would be
extracting it from the atmosphere. The colony would more likely
be in equatorial regions than in polar regions and even though
water vapour is only a small fraction of the atmosphere, you don't
need to move your equipment around to extract it. You just set
up a water extractor and let it run continuously, it can run
automatically.

The Moon? Over the long run, the cheapest place from which to
fetch water for a lunar base might actually end up being Phobos, of
all places, via the Interplanetary Transport Network. (That is, IF
Phobos' carbonaceous chondrite content is confirmed, and IF it's the
right H2O-rich type of carbonaceous chondrite.) Actually, mining and
shipping from Phobos might be an area of technology overlap: useful in
the long term for a Moon base, for supplying water and other volatiles
and minerals that are trace on the Moon; but also useful to reduce
short-term costs of Mars base set-up, until Mars surface ISRU can get
into full gear.

Phobos is still quite deep in the Martian gravity well. Why not go
get it in the main asteroid belt?

Mars might still be volcanically active:

http://www.space.com/scienceastronom...sm_041222.html

The Moon? Decidedly dead in this respect.

So on Mars, you might use geothermal sources of energy, conveniently
continuous and proximate to lava tube habitats, instead of two-week
solar heat buffers as you would on the Moon. If you lucked into a
superabundance of heat from geothermal, even if it's low grade heat,
the Mars surface greenhouse idea starts to make sense again, because
keeping it warm through nights and winters wouldn't cost so much.

Geothermal is not so easy on Earth. It would be much more difficult
on Mars. I think it would be easier to bring along a chunk of radioactive
material for a heat source than to do geothermal. But if you are in
a lava tube, you might not need much of a heat source, your problem
is going to be radiating your excess heat out. I'm not saying this
is a difficult problem, just that heating a habitat inside a lava tube
and in what is basically a vacuum is not a problem.

Alain Fournier