serious error (re. radiation shielding) in 1975 Summer Study?

On 6/26/14 5:01 PM, GARY ANSORGE dead_naked_drummer@... [ssi_list]

> As I recall, we put several men on luna w/o any significant shielding
> against cosmic radiation and most survived for a normal
> lifespan...

Yes, astronauts are allowed 50 rem/yr, or a career limit of 400 rem if I
recall correctly. This is quite a lot more than the 0.5 rem/yr
considered acceptable for the general population.

> still, for really long term exposure, several meters of rock
> have been indicated as adequate protection by nasa...and Gerard
> O'Neille...

Yes, and that's the figure I'm calling into question. On what basis was
this claim made? Does anyone know?

> as far as the planet sized mag field is concerned, the
> average strength of that field is only .05 gauss.

That's the strength 5000 km from the inner core. Show me an artificial
magnet that reads 0.05 gauss 5000 km away, and I'll be happy to use it
for shielding a colony. :)

> For space colonies,
> passive shielding that is outside the rotating portion of the colony is
> fine and could be as thick as you want...after all, it's just slag left
> over from the extraction of metals for the constructed portion of the
> colony.

If you put it outside the rotating portion, yes. Of course some modern
designs (like Kalpana One) make it part of the shell, or put it inside,
to eliminate the disastrous failure mode of collision between shield and
shell.

But anyway, I've never claimed that this problem makes space colonies
impossible. Obviously it doesn't, but it does impact HOW we design
space colonies quite a bit.

> Still, if you just have to have a mag shield, make it large
> enough to cover several cubic km...it doesn't have to be much more than
> a tesla at the source... if the windings extend over the entire surface
> of the colony...

Maybe. I'd like to see some actual references.

Thanks,
- Joe