Radiation shielding - is it necessary in the Outer Solar System?

From: "Darren Brown"
To:
Sent: Tera-feira, 10 de Outubro de 2000 01:25
Subject: [spacesettlers] Re: Radiation shielding - is it necessary in the
Outer Solar System?

[snikt]
> I don't know exactly how much it would thin out by that far but I
> think you have other things to worry about . The problem has a
> number
> of parts. Consider; first, why are you all the way out at the orbit
> of the gas giants, any habitat would need power and just about the
> best way to get that (given a space based location) is solar and the
> further out you are the harder you have to work. Placing yourself in
> an extended orbit will lower the radiation count you get from the sun
> but not the background cosmic radiation. That can be an even bigger
> problem. Low Earth orbit can use the Earths magnetosphere as a
> cosmic
> ray shield but above that you have to take/make your own. The
> primary
> radiation hitting a dense solid causes secondary radiation that can
> be
> even more damaging that the first. This means you need a very thick
> barrier, to that end several metres of metal/rock is a good idea.
> This can stop just about all the radiation or give you protection
> better than you have on the ground at sea level. With that kind of
> barrier you can put a habitat in just about any orbit you like (not
> too far in or you will have a huge heat problem, in fact you will
> have
> a heat problem anyway but too close in and you will make it
> unmanageable).
>

Yes, I addressed the issue of cosmic radiation in the first message of this
thread. The question is: according to a statistic that I have seen, the risk
of getting cancer due to exposition to cosmic radiation is much like the
risk of developing a cancer due to smoking. That is, while a solar flare can
actually kill everyone in an unprotected spaceship or in a settlement by
exposing them to lethal levels of radiation, cosmic radiation seems to take
decades to kill someone - *if* the person is ever killed. That seems to be
the reason for the presence of a shelter against solar storms in basically
any manned spaceship designed for a Mars mission; but they never have a
shelter against cosmic radiation.

Of course cosmic radiation could be greatly worsened in the case of a nearby
supernova or something like that, but such cosmic catastrophes are unlikely.
Therefore, I think that probably earlier space habitats will be shieldless,
having just shelters against MCEs and stuff. And, supposing that a growing
space population lives some decades in such "exposed" space cities (and with
correspondingly lower life expectancies), I think that perhaps they can
simply get culturally used to that and never bother to build a habitat with
the heavy shielding necessary for protection against CR. (Given much time,
perhaps 20 or 40 thousand years, they would even adapt to this harsher
environment developing some genetically coded resistance; and perhaps that
would take much less time in the case of using genetic engineering to
speedup the process.)

However, there are *no* experiments involving prolonged permanence of humans
outside Earth's magnetosphere (Mir and ISS are deep inside it), and we will
have to wait for a Mars mission or a Moon Base to see if in practice cosmic
radiation is really so "harmless" as those estimates say...

[snikt]
> Yes very true, they are rarer but that is a relative term, rarer is
> not the same as non-existent, a large number of such asteroids are
> known and of course you can move them to where ever you want. Again
> I
> don't understand why you would want to be as far from the sun as the
> Oort cloud the Kuipier belt or even the outer gas giants, this just
> makes it hard to collect power (if you use solar). If the problem is
> radiation then all you need to do put enough mass between you and it,
> far more mass than you would be able to lift from the Earth (at a
> reasonable cost).
>

It is better to say how much rare they're expected to be. Current computer
simulations used to understand how the Oort Cloud was developed show that
something around 5% of the rocks out there are not comets, but rock or metal
asteroids. This region was formed by the ejection of planetesimals from the
Solar System due to the gravitational pull and push of the gas giants, and
some planetesimals formed closer to the Sun were also "used" on that. So,
provided that you explore a lot of tiny worlds, you can find rocky and
metallic bodies in the Oort Cloud.

I mentioned the transneptunian regions (Oort and Kuipier) just wondering if
settlements there would use *any* kind of radiation shielding at all. And of
course I don't think that habitats in those places would use solar power;
colonization of the transneptunian world will be viable only if
gain-effective fusion reactors are invented. (An that maybe not that hard in
space. Although I don't have the knowledge to make the correct calculations,
I strongly suspect that one could adapt the idea of the magnetic mass driver
to make a viable fusion reactor in space. Imagine two patches of magnetic
acceleration a few tens of kilometers long and a few centimeters thick. This
device would magnetically accelerate deuterium droplets - perhaps encased in
an iron capsule - and make them collide against it other at the center of
the structure at a speed of hundreds of kilometers/second, making them enter
in fusion. Such a structure would be very expensive and difficult to build
on Earth due to gravity, atmosphere and environmental heat, but in space it
would be comparatively much cheaper and easier to construct.)

[snikt]
> Nano-technology. Instead of all the work we were just talking about,
> you simply throw a handful of nano-bots on to a rock sit back and
> wait. They self replicate, using the material around them and then
> rebuild your rock to taste, kind of makes what we are talking about
> look like steam age stuff. Just recently a team at .I believe
> MIT,
> designed a self replicating/designing robot, add the ability to
> manipulate matter at the atomic scale and you have all you need.
>

I am extremely skeptical about nanotechnology as envisioned in many sci-fi
books, and as far as I know no one has yet developed a nanorobot, just
*micro*robots. However, I think that self-replicating robots are very
promising, and self-replication robot *factories* even more promising. They
would have the same effect of cutting costs that nanorobots would have, but
would instead use "macroscopical", standard robotic technology. (Though, of
course, with great enhancements in the fields of cooperative robotics, swarm
intelligence and artificial intelligence as a whole.)

If we are going to fantasy and speculation, another alternative to
nanotechnology would be biotechnology. (After all, living beings *are*
nanomachinery - all our biochemical and biomechanical process rely on the
action of proteins and other organic molecules, that is, pieces of machinery
of nano-scale size.) Would it be possible to create biological organisms
adapted to space that could transform an asteroid into something more useful
for humans? For example, a hollow "space tree" that would "eat" an asteroid
along some decades, growing all the time until becoming a giant vegetable
many kilometers long and with a hollow filled with oxygen? (And, of course,
it would have to be made of some kind of "superwood" to have enough tensile
strength.) At the present point of our bio and space technology, that seems
very unlikely. But recently I have heard news about fungae and bacteria
colonies that developed at Mir's hull - in the *outside*; that gives me some
hope that someday, many centuries in the future, habitable space organisms
may be true... ;-)

[snikt]
> Darren Brown

Dr. Omni
ICQ# 53853815
Frum Ctico Brasileiro - http://www.egroups.com/group/fcb