Is internal dirt counted among radiation shielding?

> The problem here is that dirt is not "under foot" when you are talking
> about large habitats. Yes gardens, flower beds and growing area may have
> that much dirt, but you are not going to want to put soil under a house,
> office or other building. Adding that extra soil and spinning it up would
> mean constructing the habitat to much higher torsional strength than
> would be necessary. You would only want to add that weight to the places
> you really need it.

Thanks for your insight. However, artist's illustrations always show lots of trees, hills, streams, and other geographic features, mixed right in with the houses and other buildings. I suppose the hills and houses could be supported underneath by an empty steel shell, but it's certainly not an approach I've heard advocated before. I assumed those would be dirt all the way down to the shell.

As for required torsional strength, you'd have the same (or at least, a similar) issue for any design that uses integrated shielding (as opposed to separate, non-rotating or counter-rotating shielding). I realize that many of the later designs had the shielding separate, for exactly the reason you mention. Still... I can't shake the feeling that if you think of your shielding as something to plant trees in, sculpt into hills and valleys, sink foundations for tall buildings into, etc. -- and realize that you're going to want to do all those things anyway -- then it seems much simpler to have no "shielding" at all, build the shell a bit stronger, and add more dirt. (The dirt could be mostly lunar regolith, with extra nutrients added only in the top layers as needed.)

But I'm sure it ultimately comes down to the numbers, and the relative cost of various materials. I'll look into it further. But it's very helpful to know that the chief objection to this approach is the weight of the dirt, and not some fundamental reason why dirt can't be used as radiation shielding.

Thank you,
- Joe

Joe Strout -- joe@...