shielding

>From Roy Lent 17 Mar 2001, (on the engineering issues mailing list of
the L.U.F. www.luf.org)
> I read that a colony must be shielded from high energy
>solar radiation coming from all directions... I spent
>some 5 hours pursuing the subject of shielding from
>solar flares, on the Web. I have found statements that
>the "near Earth radiation environment is drastically
>different from that in deep space", but without
>explaining in any detail just how it is different.

The geomagnetic field distorts things in 'near-Earth space', while
anywhere more than 50,000km out, the solar wind is dominant. Around
other planets, their magnetic field is important. Jupiter's magnetic
fields, if visible, would appear from here as about the same size as
our Moon, and it's magnetotail sweeps out past Saturn. Most of its
moons are uninhabitable without extensive shielding due to the
ionization belts. (A colony would fare well, but EVA would be
impossible, and anything would need heavy shielding -On the other
hand, ED tethers would work wonderfully)

>I also find statements that there are no significant
>magnetic fields in deep space, i.e. far from the Sun
>or planetary bodies.

The heliopause (where the solar magnetosphere is effectively bounded
by the overall galactic fields) is at about 200 AU. (We seem to be
near the center of a huge interstellar bubble of rarified space;
remnant of an ancient supernova.)
Beyond the heliopause, solar events are negligible, and cosmic rays
are the main threat. These themselves may not seem to be too much of a
threat (~20-50 rem/year), but then again, we are designing for a long
term city, with fetuses, babies, and children. We'll need the full
~5tonne/sq meter (2 meter) cosmic ray shielding for anything beyond
this (not to mention big mirrors, but then again, it's only aluiminum.
Out this far, the Sun is only a particularly bright star, and others
may be as good to aim the mirrors at, and cometary bodies this far out
are juicy, with lots of volatiles).
As well, if we don't have 2 meter shielding to deal with cosmic ray
secondaries, anything in the path of the particle will throw off a
spray of secondaries; internal structure, soil, whatever. Anything
less than ~5t/m^2, and you're getting a lot of secondaries.

>So, I am perplexed. What is it that diverts, distorts
>or deflects the paths of the particles coming from
>the Sun so that they will come at the colony structure
>from all angles making it necessary to have heavy
>solar flare shielding on all sides of the colony?

Maybe I can't answer satisfactorily, other than to say that the solar
magnetosphere is highly active, with swirls & gusts all over.
A prominence is a massive blast of ionized gasses bent into an arch
to fall back into the Sun. A coronal mass ejection is one of these
which escapes the Sun, and is blown out at 300-600km/sec. The solar
magnetic field definately affects arching movements out well past 1AU,
with the arch formation easily being 2+ light minutes across, sweeping
throughout interplanetary space.
http://sohowww.nascom.nasa.gov/bestofsoho/bestofmenu.html
Shows some of the violence & how energetic this space weather can be.
(I was hoping to find an animation of a CME blasting past Earth)

> This is, of course, assuming that the colony is
>in deep space and not in a near Earth orbit.
> And ignoring, for the moment, cosmic radiation. The
>colony in question would be in a solar orbit, even
>out of the plane of the ecliptic.

Either way, there's no easy way out. The equivalent of ~2 meters of
sand, all over, or cosmic ray secondaries get you.
A bit of hope appears in the Magsail. It effectively blocks the solar
wind from the ship, as it transfers the momentum of the wind to the
ship. If the superconductors are obtainable, we've got
station-keeping, and even some tiny propulsion to a colony. Amazing
maneuvers are possible to a ship within a planetary magnetosphere.
The cosmic rays are still blasting through, so it seems you're still
stuck with a lot of rock (or something) around anything meant for
long-term habitation.