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

--- In spacesettlers@egroups.com, "Dr. Omni" wrote:
Hope you enjoyed your travel,

>> --------------------. The normal levels of radiation are not your
>> main problem. What you would have to guard against is a Mass
Coronal
>> Ejection. This will spread as it moves but is more like a torch
beam
>> than a candle flame. As such it can do more damage at a greater
>> distance. You would need to protect yourself out there.
>>
>
>Yes, I know that Mass Coronal Ejection (MCE) can go far away and
still keep
>power, but I still don't know *how far* away. The orbit of Jupiter?
Neptune?
>I would like to see a function describing MCE power x distance or
something.
>Occasionally, I'll browse through some papers on the subject and see
if I
>can get more detailed information.

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).

>> Of course if you can get enough equipment out that far you have all
>> the mass you would need, sitting around in nice handy sized lumps.
>> In fact with a large mirror, a big bomb and a lot of ice (pick it
up
>> from a passing comet) you have all you need to make your own
habitat. You
>> just use the mirror to heat up a local rock to a soft half melt (
>> lots of metal if you please), insert bomb and pack with ice, set
off bomb
>> to boil ice and expand the rock. Wait to cool, insert dirt, people
>> and settle back to watch.
>>
>
>That's one of the ideas regarding small-scale terraformation on
asteroids.
>I've thought of another one that would consist in simply cutting a
>cylindrical hole some kilometers in diameter through a rocky or
metallic
>asteroid. An extremely powerful laser could be used to cut the
cylindrical
>section of this hole, and the hole section could be moved away using
mass
>drivers, leaving behind an asteroid with a hollow cylinder. The ends
of the

The laser would need to be able to vaporise the rock and not just a
small patch but a huge amount. Even just cutting a plug out of the
centre of the rock it would still need to be far more powerful than
anything existing today, makes a handy weapon. Then you need move
the
plug out of the middle, that would be the easy part. First you would
need a power source for the laser, a large mirror with a generator at
the focus would do. Then the laser, with the kind of power it would
be using it can't be small. Something to dump the heat from the
laser, they aren't all that efficient and even a few percent (and it
would be more than a few percent) means you'll have a lot of heat to
get rid of or bake your crew. Then you need to either stop the rock
from rotating/tumbling ( a lot of propellent and power ) or you will
need to match exactly in order to be certain the cut was in line and
going where you wanted. Once the plug was cut you then need to move
it, this is in fact the easy part, just use a small/large (depending
on the size of the plug) rocket motor and push, you could even use
the
laser to vaporise part of the rock and act like a rocket exhaust and
let Newton do the rest. You will also have to use the laser or some
large explosives to shape the outside of the rock or you'll end up
with a very odd wobble to your habitats rotation and the
consequential
variable centripetal acceleration giving you a changing sense of
gravity.

>cylinder could be covered with transparent domes (or
yet-to-be-invented
>super-resistant polymer sheets) and the hollow could be filled with
an
>atmosphere; and finally the internal surface could be covered with a
>biosphere, powered by mirrors strategically put near the ends of the
>cylindrical hollow, reflecting sunlight into the inside of the
asteroid.
>Finally, the rotation axis of the structure could be tilted in order
to make
>it perfectly perpendicular to the orbital plane of the asteroid, thus
>shielding the internal biosphere against solar activity.

This would shield against solar radiation but not cosmic radiation a
better idea is to enclose the entire habitat and then to pipe
sunlight
in through dome and mirror arrangement and sent through a tube
running
down the axis of rotation. This is then could be used in the manner
of a florescent light tube. Not as pretty but safer.

>However, although they're very beautiful and elegant, those asteroid
>terraformation projects have a lot of unknowns. First, if I remember
well,
>rocky and metallic asteroids are rarer than carbonaceous ones, and
they get
>rarer as you go far from the sun. Perhaps they're not a viable
alternative,
>let say, in the Kuipier Belt or in the Oort Cloud. Second, even
though

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).

>they're made of rock and/or metals, it is not clear if they have
mechanical
>resistance enough to withstand a centrifugal effect simulating 1.0 g
>gravity. At that point, solar-powered melting of the asteroid enters
into
>scene in order to give the rock the necessary mechanical strength.
But it is
>not clear to me if radiation-driven heat would work properly to melt
an
>asteroid until a depth of several hundreds of meters. Are there any
>civil/metallurgic engineers here who could give their opinion on
that?

Currently we think that many of the metal asteroids are pure (or near
pure) metal (Nickel / Iron with traces of other metals) and as such
should have the ability to stand up to the stress of spinning fast
enough to provide a 1g environment inside. Rock on the other hand
has
very little tensile strength (but huge compressional strength) and
would not be able to stand up to this. As for heating the rock (I'll
call it a rock because calling it a metal sounds a little odd) it
could even turn out to be easier than at first it seemed. If you
have
a look at http://near.jhuapl.edu/ the near project you will see that
the latest reading show that EROS is;

Quote "Findings from NASA's Near Earth Asteroid Rendezvous (NEAR)
mission - appearing in a special section of the Sept. 22 issue of the
journal Science - confirm that asteroid 433 Eros is a consolidated,
primitive sample from the solar system's beginning" END QUOTE

The important part being the word consolidated, this shows that EROS
has some structure (there was a time when it was thought it was just
a
huge pile of rubble and indeed it could still be in places or other
asteroids could be). In some ways it would be easier if it was just
a
rubble pile (easier to shape) but being consolidated it should
conduct
heat well making it simple to bring to a melt.

>Due to all those unknowns, I still envision completely artificial
habitats,
>build with industrialized steel, plastic and glass, as the most
generic
>solution when it comes to space habitats. They could be built
anywhere using
>raw materials gathered basically from anywhere. Also, they would be
much
>lighter and could be more easily moved on demand. But asteroid
habitats will
>always be the most charming solution, I think... ;-)

Lighter is not always better, if a modest but largish hunk of rock
was
heading my way I would like to have a nice thick skin thank you. But
if you are going to build your habitat in orbit (and it would be the
cheapest way) then you will need a lot of equipment and people to do
it. Not only do they have to turn iron in to steel (not easy) they
will most likely get the raw martials from the same place that I
would
get my rock. Your laser would need a power source, the same mirror I
want to use to heat up my rock? Of course there is one technology on
the horizon that could make all of this out of date and pointless.
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.

By the way I added a couple of links to the eGroups site.

Darren Brown