Using Concrete to build space ships...

"You need the same mass no matter what you use as
shielding. To get the same level of radiation as sea
level on earth, you need 101kPa/9.8(m/s^2) = 10300kg
of shielding per square meter. The moon
miner's manifesto numbers are for a radiation level
much higher than earth sea level. To reduce it to
sea-level radiation, you would need four or five
meters of regolith or ten meters of water."

Thanks Ed for the detail.

Correct me if I am wrong in this assessment:

In the early stages of human space development life
will be like mice hiding from the radiation/bone loss
cat. Stay out in the open too long and you will get
fried (caught) one way or another.

The best shelters will always be the moon under enough
regiolith to block anything short of an asteroid.
Next best will be in some bulky structure either
inside of an asteroid or on the side of it. Both will
be built in place or the fuel costs will be
extravagant.

Astronauts will need very quick travel to the
moon/asteriods to prevent getting fried. This means
only high impluse propulsion systems and no round
about means of getting there. Mass drivers and ion
engines would not do this. Nuclear would leave wakes
close to home - go have fun with the enviromentalists.

In this model the cheapest oxidizer is oxygen brought
up from the moon and kerosene or hydrogen brought up
from earth. Kerosene is nice since don't need to
pressurize it or worry about boiling off if the sun
shines on it.

- Thor