Most studies I've seen always put a great deal of emphasis on an external (usually non-rotating) radiation shield. Yet inside the rotating habitat, we have landscaping, which implies at least a meter or two of dirt. Elsewhere, I've seen that a meter or two of dirt provides robust radiation shielding.

So, it would seem to me that you could forego the external radiation shield, at least for the areas of the habitat which are "underfoot." A person might have to take precautions (e.g. wear a radiation monitor) when digging holes, but at most times the dirt should provide sufficient shielding by itself. If an extra safety factor is wanted, then add more dirt -- this only enables the planting of bigger or more varied trees, and deeper foundations for tall structures.

What am I missing here?

Thanks,
- Joe

P.S. Is there a Wiki anywhere dedicated to space habitat topics? It seems like that would be an ideal place to collect information like this, along with primary references. Wikipedia is a bit too general for the level of detail I'd like to see.

Joe Strout -- joe@...

Most studies I've seen always put a great deal of emphasis on an external (usually non-rotating) radiation shield. Yet inside the rotating habitat, we have landscaping, which implies at least a meter or two of dirt. Elsewhere, I've seen that a meter or two of dirt provides robust radiation shielding.

So, it would seem to me that you could forego the external radiation shield, at least for the areas of the habitat which are "underfoot." A person might have to take precautions (e.g. wear a radiation monitor) when digging holes, but at most times the dirt should provide sufficient shielding by itself. If an extra safety factor is wanted, then add more dirt -- this only enables the planting of bigger or more varied trees, and deeper foundations for tall structures.

What am I missing here?

Thanks,
- Joe

P.S. Is there a Wiki anywhere dedicated to space habitat topics? It seems like that would be an ideal place to collect information like this, along with primary references. Wikipedia is a bit too general for the level of detail I'd like to see.

Joe Strout -- joe@...
http://www.verex. com/

> 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@...

"Is there a Wiki anywhere dedicated to space habitat topics? It seems like that would be an ideal place to collect information like this, along with primary references. Wikipedia is a bit too general for the level of detail I'd like to see."

I've just started a new wiki and will have a section for space habitats very soon.

http://www.cygo.com/wiki

George
cygo.com

> I've just started a new wiki and will have a section for space habitats
> very soon.
>
> http://www.cygo.com/wiki

Thanks George, this is a useful service. I would suggest that, whenever one of us goes to the trouble of looking up some habitat-related references or doing some calculations, that we enter it on the above wiki, so that everyone can find and benefit from it. I'll start doing this today (I'm currently looking into issues related to radiation shielding).

Best,
- Joe

Joe Strout -- joe@...

> So, it would seem to me that you could forego the external radiation shield,
> at least for the areas of the habitat which are "underfoot."

Sorry, to follow up my own post here, but I've just found the Kalpana habitat design by Al Globus et al., described first in 2000 [1] and just presented again at the 25th ISDC [2]. This design does exactly what I was thinking: the radiation shielding is all inside the pressure shell, in the form of lunar regolith which doubles as soil for plants. The authors argue (correctly, I think) that having an external non-rotating shield introduces an unnecessary risk of catastrophic failure (i.e., collision with the shield).

The also happen to mirror some other design decisions I'd been favoring, such as having nested internal cylinders (which I call "decks") and the use of artificial lighting for agriculture. It's satisfying to see that people smarter than myself have come to these conclusions as well! Of course they also thought of some things I had not, such as the rotational instability of a long cylinder.

This is a very interesting design, and if you haven't seen it already, I highly recommend a read of the references below.

Best,
- Joe

[1] http://alglobus.net/NASAwork/papers/KalpanaOneASCE2006/KalpanaOneASCE2006.pdf
[2] http://alglobus.net/NASAwork/papers/NSS2006KalpanaOne.pdf

Joe Strout -- joe@...