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

From: "Darren Brown"
To:
Sent: Quinta-feira, 28 de Setembro de 2000 09:48
Subject: [spacesettlers] Re: Radiation shielding - is it necessary in the
Outer Solar System?

> Dr Omni,
>

Hi Darren, sorry for taking so long to reply your message, but I was
traveling off-country... I'll soon move to a more reliable free POP3 server
for receiving my E-group messages regardless of where I am.

> Hello from Australia. 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.

> 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
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.

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
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?

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... ;-)

>
> Darren Brown
[snikt]

Dr. Omni
ICQ# 53853815