On Jun 18, 12:14 pm, Alain Fournier wrote:

"I'm not sure exactly how one would pressurize such lava tubes."

I have not proposed pressurizing lava tubes. I was addressing an
apparent concern of yours: whether they had enough volume for
agriculture. I was merely pointing out that the size of some lunar
lava tubes dwarfs that of any structures (including greenhouses)
currently envisioned for formal Mars missions. The main point of
these lava tubes would be to have a roof over your head that shields
you (and your crops) from CGR, solar storms, dust and temperature
extremes. What you build *inside* them doesn't have to be proof
against those threats -- meaning less mass to take along to Mars, less
time spent in construction of habitats, less maintenance complexity,
more safety in what's otherwise a hostile environment not too
different from that of the Moon.

I don't propose lava tubes as a *substitute* for artificial habitats
or greenhouse, even if they have some speculative potential for that
in colonization scenarios.

Remember, the topic here is "technologies for Moon mission usable for
missions further out".

"... But longer term, using the entire volume of the lava tube is a
very interesting prospect. But then again, longer term, you will
probably have much a bigger population and you might want to use the
entire lava tube for human occupation and let the farming be done in
greenhouse on the ground."

When would that be? When Mars has a population of millions?

Humoring you, for the moment: Look at intermediate stages of economic
development. You seem to be assuming that every inhabited lava tube
must grow its own food. Well, how French of you! ;-)

Why can't some lava tubes become more specialized for food production,
others for habitation, if the initial tube gets too crowded for
farming? There will be no shortage of lava tubes for the time being.

There are major industrialized nations on Earth that get by fine
without 100% food self-sufficiency. I live in densely-populated
Japan. My kiwi fruit comes in from sparsely-populated New Zealand.
Even my "Made in Japan" tofu is mostly soy from the sparsely-populated
United States. I don't buy Japanese wine made from Japanese grapes,
because it's wretchedly awful -- but I do have two bottles of
Australian shiraz at the moment. So if I lived in a lava tube on
Mars, why would I buy my own tube's food, if I could get it cheaper
(or better) by importing from other lava tubes? Or for that matter,
if I could get it shipped down to me from Phobos Farms (TM)? After
all, might be some delicacies that can only be grown in
weightlessness, for all we know.

If Mars starts out a one-tube settlement, and the population grows to
the point where living space is in competition with agricultural
space, eventually somebody will figure out there's a business
opportunity in the higher food prices inevitably resulting. The cost
of space in a neighboring lava tube might be near zero, and the
capital costs of developing that new tube for agriculture, plus the
continuing cost of transporting food back to the old tube, might still
be cheaper than farm-space rent in the old tube. At that "tipping
point", the old tube's farm-spaces turn rapidly toward residential and
commercial uses, the new tube becomes mostly farm-space.

It's a story that's played out for literally thousands of years in
terrestrial economies. Yes, even in France, not so many centuries
ago. It's a story that might play out on the Moon before anybody even
gets to Mars. It's hard to see why the economics of agricultural vs.
residential land use would change dramatically just because you're no
longer on Earth.

In any case, I thought we were talking about lunar mission technology
reusable for Mars missions, in the foreseeable future, not about
colonization.

I think we can solve the technical issues above, it might not be as easy
as it looks, but we have built lots of stuff that can operate in harsh
environments. I see no reason why the above[list of problems with
surface greenhousese] would be impossible to solve.

Engineering is not about what's possible. Lots of things are
possible.

But what gets done? The things that are feasible.

If agricultural equipment engineered for lunar lava tubes ends up over-
engineered in some ways for Mars, at least it's already been
engineered. It might require only slight adaptation for Mars. That
reduces mission development costs and gives you a margin of safety,
with proven equipment, upon arrival. Setting up agriculture on Mars
would take time, during which you might be relying on food drops from
the mothership's closed-cycle (no longer!) garden operations in Mars
orbit. Afterward, if some mission staff happen to have some time to
spare and can afford to take the risks involved, they might
*experiment* with growing stuff in greenhouses on the surface of Mars,
on a small scale, to see if it might be made *feasible* for future
missions. However, even if it turns out to be possible, it will
probably be inferior to growing food in lava tubes in terms of what
matters: price/performance. What you end up using to grow food will
probably be more like what you used on the ship that brought you, in
an environment more like the ship's. Remember: even Martian "dirt"
might not be free: you might have to detoxify it.

If what you're talking about is colonization, that's a different
topic, and a future none of us is likely to see. I thought the topic
was "technologies for Moon mission useable for missions further out".

But even in the colonization scenario: if I lived on Mars, I wouldn't
buy food from surface farms if I could get the same quality at a
better price from farms hosted more cheaply in lava tubes. So even if
the surface greenhouse problem is solvable *technically*, such
greenhouses will end up being only scientific curiosities if they
can't produce food more *economically*.

To repeat: greenhouses on the Martian surface will get exactly one
benefit from being on the surface: direct daytime pass-through of
sunlight at frequencies useful for photosynthesis. That's IT.
Everything else about being on the surface is just a source of added
problems. Solving problems costs money. Money that nobody will pay
if there are cheaper solutions that are just as good.

If some multi-billionaire just HAS to see a beautiful dome with
greenery in it, sparkling under the Martian sky, before he dies, to
fulfill his SF-illustration-fired boyhood dreams of what a Mars base
was *supposed* to look like, with cost no object, well ... then maybe
it'll happen. Where costs matter, it probably won't. Stuff in space
never ends up looking like the "artist's rendition". It always looks
like it was custom-engineered for a highly unusual environment by the
lowest bidder. Funny how that works, eh?

Throw out the SF illustrations. Throw out your old intuitions. On
Earth, the only agricultural product grown in caves is the truffle, an
expensive delicacy. On Mars, maybe tequila will be the drink of
choice for those who feel compelled to consume conspicuously, but only
if it's distilled from those expensive *surface-grown* greenhouse
cacti, with a bottle costing a month's average pay packet.
Connoisseurs will claim to be able to tell the difference. Blind
taste-testing will reveal that they are deceiving themselves, but they
will be undeterred.

-michael turner