The 100 displacement ton sphere will have a hull surface area of
615 m^2. At a (sphere wt= x 0.8?) normal hull, it would weigh
1320 tons. That's 2.15 tons/m^2. Or 215 g/cm^2.
Now, I don't know how much you all know about real
spacecraft design, but 200 g/cm^2 is at the low end of what's healthy
for long-term radiation exposure in deep space*. Permanent facilities
ought to be more. (about a factor of two more, maybe three. But
200 g/cm^2 is in the right ballpark).
WHat do current spacecraft weigh? about 2 g/cm^2, ranging up
to 3. Why do they get away with this? They stay within earth's magnetic
field (which deflects both solar radiation and Galactic Cosmic Radiation or
GCR) and out of the high-radiation Van Allen belts.
So, to answer the 'why' of 'why are they that thick' we can plead
crew safety 8-), and the 'how can i make it less'; if it's for near-orbit use,
and you don't mind a (lightly) irradited crew, it can be a lot less.
- - -george william herbert
[email removed]
* deep space radiation falls under two sections; that produced by the sun
in solar flares (intermittent) and the cosmic ray background, constant
in the galaxy. Generally, the same amount of shielding will keep
flare doses at safe short-exposure levels and the continuous GCR at
safe long-exposure levels. I can copy some NASA info on this for anyone
that wants it.