FLASH! - New Report says plants love SPS, why not environmentalists

Martian atmosphere? IIRC that's about 1% of earth...doubt that would shield
much, and even if it does, than a earth like atmosphere inside an inflatable
greenhouse would protect as much as 100 times as an equivalent amount of
Martian atmosphere. Plants developed on earth when the atmosphere was much
denser and rich in Co2 than it is now, so all plants can use a much greater
amount of it than it is present today in the air (this is why commercial
greenhouses use co2 generators to get accelerated growth rates), so it is
certainly possible to grow plants in a much denser atmosphere than earth
one. Add the two things together and you probably need only sixty-seventy
meters of dense greenhouse air to have the same protection given by 10000
meters of Martian atmosphere.
But the point is moot IMHO, because the whole idea of inflatable greenhouses
seems something straight out of a sixties movie to me... :) why inflatable?
If you want to build greenhouses on the moon, or in orbit using moon
materials, you got abundance of raw materials to make glass. I'm pretty sure
that would be enormously cheaper than any flexible transparent cover that
can hardly be manufactured with local raw material... glass can be made
cheaply and used as building material itself, can be meters thick, and still
let pass plenty of light while providing an efficient shielding from
micrometeorites as well as radiations. Can be easily manufactured and as
easily maintained, replacing any damaged slab and re-melting it to produce
spares. It can be made including an amount of impurities that helps shield
radiations. This assuming you want to "build" greenhouses which is a daft
idea in itself, always IMHO, because would be much better dig them instead.
Then you'll have a really nice solid rock and lunar concrete shielding all
around, and all you need is a mean to get light in. This can be better
achieved with large mirrors that reflect the light down through apposite
"windows", and both these components can be made so that the mirror coat
will reflect only a minimum of radiation if any at all and the window itself
shield from the rest.
Using water for shielding is another nonsense as far as I can tell because
to begin with how you keep it liquid, without using even more power to heat
it than it would be required to generate artificial light? Incidentally
solid and even better underground greenhouse would also be much more
efficient at thermal insulation, how exactly an inflatable greenhouse is
supposed to keep 30 or 40 C^ inside when the outside temperature goes down
near the absolute zero? And what happens if it's pierced by an accident?
Kaboom.
Even for orbital structures I would imagine a very thick walled box of
concrete with an as much thick transparent wall at the end facing away from
the sun, and a mirror to reflect the light in, is a much cheaper, safer,
easier to maintain, flexible and solid design than any inflatable
transparent structure, which are not very reliable even on earth, go figure
in space... ;)
IIRC Zubrin "plan" was based on the existence of hot pools of water
underground on Mars, which is like to say if the planet is habitable we can
inhabit it. Great. AFAIK though, there are no such pools, and Mars remain a
frozen airless hellish inhabitable ball of rock. For all we know there may
not be water at all either, as the recent about-face about water on the moon
shows. If we can't tell for sure if it's water what we see on the moon I
tend to be cautious about it existing on mars. Polar caps are mostly frozen
Co2 anyway if I'm not grossly mistaken.
Bottom line, there is no need to travel all the way to Mars to find
unbelievably cold, low gravity, un-pressurized sterile mountains of dust,
there is plenty much closer. Anything you could maybe theoretically possibly
if maybe perhaps do on mars you can at least as probably do it on the moon,
and for sure it would be a lot cheaper and safer. Probably a thousand times
cheaper and safer.
As for "terraforming" a planet, apart the immense scale of the project that
makes it as realistic and probable a possibility as that you win the lottery
without playing, for the pure pleasure of the speculation why mars? Why not
Venus? At least it has an atmosphere, and is able to retain it. You "only"
need to break the greenhouse effect to cool it down, and then clean up some
sulphuric acid, a kids game... :)
Beside we could colonize Venus as it is, without terraforming it. Venus is
usually thought as impossibly inhospitable, but conditions in the atmosphere
at an altitude of around 50 kilometres are relatively mild: the temperature
is about 70 C, with a pressure of about 1 atmosphere. A paradise compared
to Mars, even without considering that there is water (albeit admittedly in
the unpleasant form of sulphuric acid), plenty of metal and life essential
gases (apart oxygen) and that the gravity is nearly the same as earth. There
have been already interesting ideas about colonising Venus using aerostatic
habitats, since the atmosphere is so dense, breathable air is a lifting gas
on Venus, so a shell of some kind full of breathing air and with a ballast
of soil would elegantly float at the right height. It won't even need to be
particularly strong as at the right height the pressure is conveniently
balanced at about 1 bar.
Access to the surface is relatively simple from an aerostatic base, since
the thick atmosphere allows flight by airplanes and balloons.
IIRC Venus is also closer, in terms of flight time, to the asteroid belt
than either the Earth or Mars, so makes a better starting point even for
asteroid mining operations.