jacob navia wrote:

Le 11/10/2016 à 12:29, Fred J. McCall a écrit :
However, shielding is not that difficult.

In principle.

In practice we just do not know.


Of course we do. We know what the radiation environment looks like.


No shielding has been tested in
interplanetary space till now.


But we know the radiation environment and the shielding properties of
various materials. This is NOT a hard problem. It just takes mass.


The crew needs to be shielded on Mars
too, but that could be easier if they went underground. A deep cave and
you should be OK.


Also a shallow cave. Or a trench with a few meters of dirt mounded
over it. Or...


But you shouldn't go out for extended periods since Mars offers no
shielding from radiation from cosmic rays. The ultra thin atmosphere is
no protection at all, and there is no planetary magnetic field.


The "ultra thin atmosphere" is quite a lot of protection, actually,
and eliminates over 60% of the radiation.


You have to stay as much as possible in the cave.


Not so much.


Planet too small, gravity is one third of what is on earth. Consequences
in terms of bone loss are unknown but probably not very good.


You can't equate total ignorance and then assume bad news.


Look, I am not at all against humans going out of the earth, to the
contrary. But I see no need to sacrifice people just... for what?

What can humans do that they couldn't do safely from earth?

OK, driving rovers without a 15-30 minute time lag is a reason, maybe a
valuable reason. But in that case is better to live in orbit rather than
in a cave...


But 'in orbit' gives you a much worse radiation environment to deal
with, you have no hope of in situ use of resources, etc.


Artificial gravity is easier to do in space than on the surface of mars.
Better conditions are easier to realize in a station orbiting Mars than
trying to scrap a living in the surface. Short trips to the surface
could be done of course, but for the bulk of exploration just staying in
orbit would be easier.


No, because you want PEOPLE doing the exploring. A couple humans on
the surface with a small vehicle can explore more than a rover can do
in years.


Induced radioactivity because of cosmic rays bombardement during eons
makes the surface of Mars slightly radioactive,


Not enough to care about.


and besides, it is stock
full of substances that are very toxic for humans.


So is Earth.


Mars dust is very
sticky, probably electrically charged. All those problems are avoided in
orbit. Machines do not care about those hazards, resist very well
decades of Mars conditions without any problems.


Well, no. Your 'sticky dust' problem, if it exists, is a problem for
MACHINES, not people.


Humans have a machine roving around in Mars since January 2004 and it is
*still roving around*. Only problems are a stuck wheel and the flash
memory that gave up the ghost some months ago.


And humans on site with a vehicle could accomplish more in a matter of
weeks than the toaster has in its whole existence.


TWELVE YEARS!

That proves that toasters have quite a good price/science ratio. Humans
are very fragile, as you know.


It proves no such thing. If humans cost 100x but return 1,000x data,
humans are a better deal.


But it would be nice to go there, of course. As a thrill, or for
scientific reasons, to study a planet and the biology there.


Or just to live. You know, like we do in North America.


All NASA missions point to a biology in Mars, and that will be surely
one of the big discoveries of this century. But humans in Mars could
swamp what that subterranean microbial life could tell us about
ourselves. It is a second ecology.

It seems that life in Mars was very similar to life on Earth since a
microbiologist discovered formations that are identical to fossil
formations in Earth. When Mars was wet and had an atmosphere, the
microbes were very similar since they produced similar fossils.


So nothing new, then. You can't argue it both ways. Either there's
something new, in which case we'll be able to tell it from Earth life
when we find it, or there's nothing new and we don't need to worry
about contaminating it.


Mars is full of secrets, let's explore it wisely. Developing a
technology that carries people to Mars will be done, but it will take
decades.


For some value of 'decades' that's approximately equal to between one
and two.


Biology will give us the solution. Genetic engineering of a space suit
skin, redesigning the DNA repair machinery so that radioactivity and
cosmic ray damage doesn't affect us as much would allow for less shielding.

To design a body that can live in Mars easily.

That will take some time.


Which is why we won't wait for any such silly thing.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn