# When estimating radiation doses inside a lunar habitat, what assumptions are made as to shape?

The current estimate for how much shielding is needed for a long-term habitat on the Moon is a minimum of 700 g/cm2 of regolith, and 1000 g/cm2 for the levels at sea level on Earth. (The radiation dose on the lunar surface is not really known, so this is an estimate based on highly complex modelling.) That same estimate is mentioned in this video on civil engineering on the Moon:

I've been designing such habitats for a project to create a virtual lunar colony online. One area uses a configuration designed to allow in lots of natural light from above while still keeping the overall radiation low enough that a person can spend lots of time there. In that process I've been using the assumption that what they mean is that at least 700 g/cm2 in all directions yields this result. Today it occurred to me that it could instead mean that case over a hemisphere. At any rate, the only scenario where exactly the same amount of material stands between you and the outside environment is when you are standing dead center in an empty sphere with walls of uniform thickness, all of the same material (and you are also a dimensionless point, if one is especially a stickler about it).

Up to now I have been subtracting directions in which there is material of greater than 1000 g/cm2 from the total radiation dose, and I have been adding on higher radiation doses for the directions where there is less, as a proportion of all directions. It seems to be the best way to estimate dose within a given design. I also consider the proportion of time that a person might spend in an area with a given dose.

If these estimates aren't based on that simplification of a sphere, those results are off. If it is a model of a half-sphere, then I need to double the numbers. Or maybe it is modeled on something much more complex, like a point under a plane of that much material.

Does anyone know what assumption is used?

• You may be overthinking this. If you build a box with walls thick enough to give 700 g/cm2 of material, the radiation dose will be acceptable anywhere in this box. Commented May 2, 2016 at 7:52
• @Hobbes Yes, but a box doesn't have windows, or places where natural sunlight enters. If people are ever to live on the moon, they will need those things, preferably lots of them. Living in a box is no fun, especially when you can't go outside without a very bulky and clumsy spacesuit. For instance, a series of beams laid east-west across a large trench, with a direct view of the sky in between, lets in enough sunlight for plants to grow, and gives something of a feeling of being outside. But what would the dose be there? How do you size the beams to lower it? Commented May 2, 2016 at 14:28
• A bunch of beams with space between would reduce the exposure by the % of the roof that was beams. You're starting from .25 Sv/yr, you're not getting a reasonable amount of light through without letting in a lot of radiation. Commented Jun 2, 2016 at 0:04
• You can have windows without radiation, though--don't let the windows see the sky. Rather, the windows look upon mirrors. Since the radiation can't turn a corner you can build a path light goes through but which provides shielding. Commented Jun 2, 2016 at 0:05
• @LorenPechtel - Yes, i've used that concept in different areas, but feel there is value to a space where lots of natural sunlight comes in from above over a large area, so it feels a bit like the outdoors. I added a link in the question to a description in the project's forum, it hasn't yet been added to the main page. Here it is again. Commented Jun 2, 2016 at 1:27