Kalpana one

--- In spacesettlers@yahoogroups.com, Al Globus wrote:

> > Also, your design doubles the shielding accepted for the NASA
> > Summer Studies; ~10tons per sq meter. I live near Denver, at about
> > 1.6km ASL, where they settled on the shielding requirements (while
> > I'm not at 1/2 atmospheric pressure, I am above half of the
> > atmosphere's mass, so about 5tons/m^2).

> Actually, the NASA summer studies called for 4.5 tons/m^2. But
> remember that in Denver you are only exposed to cosmic radiation
> coming from the sky. Everything coming from the other side of the
> Earth is blocked.

> That said, I think 4.5 - 5 tons per m^2 is probably reasonable,
> subject to further study. It doesn't really change much about
> Kalpana One, but it does cut that mass in half and make everything
> about two times easier.

Al, we went through this very issue almost 3 years ago:

You're positing that the shielding requirement needs to be doubled
because the Earth is blocking half of the radiation. No. Imagine that
you are standing with a radiation meter in Denver. You take a reading.
The source of the radiation is coming from the sky above you (let's
discount sources in the Earth itself. The radiation reading is the sum
total of radiation that you have to address, not double the amount.

Now, imagine that instead of standing in Denver, we could erase the
mass of the Earth but leave atmosphere in place as an outer sphere
that enveloped the Earth. You're positing that the radiation level
would suddenly double because the mass of the Earth has been removed.
However, you're neglecting the role of the atmosphere on the other
side of the sphere - it would have attenuated the radiation level to
the same degree as the atmosphere above Denver, therefore there would
be little residual radiation left for the bulk of the Earth's mass to
block.

Therefore, the model for shielding should only account for a radiation
intensity that comes from one direction. In any Habitat, there will be
shielding all around the circumference which will envelop the Habitat
in the same fashion that the atmosphere envelops Earth.

Your shielding requirements can be halved back to the orginal Summer
Study requirements.

TangoMan