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In the Reference Mission, we are waiting until after the crew leaves on the first mission to worry about burying the habitat. That's where the robots come in. Since the robots should be able to handle the job without on-site human presence, we can save crew time for doing things that are best done with human hands and eyes. Besides, saving the shielding job for later extends the commercial value of the mission because it moves some of the fun back down to Earth.
For a two-week stay, radiation shielding isn't a major problem for the crew. Our thermal problem during that time will be rejecting heat from a fully powered habitat, so waiting to snuggle under a blanket of regolith will be an advantage.
Insulation works by slowing heat flow. When the habitat is fully blanketed it does this by using the regolith covering as a thermal capacitor. Until then, we can smooth out heat flow using multi-layer insulation (MLI) to reflect infrared radiation (that is, heat) back into and away from the spacecraft. Most spacecraft today use MLI thermal blankets to control heat flow.
We assume it's obvious that since the moon rotates a great deal of the habitat will be exposed the Sun, so let's consider what happens if we only shield that part. There might be considerable advantage to the idea of not shielding the other parts. There is still a lot geometry around the module that would not be exposed to direct sunlight.
Most of the nasty radiation comes from the sun, so we might get away with less shielding in the permanently skyward directions. The MLI (see above) and mass of the pressure vessel might be sufficient. Who's a radiation expert? We need some serious analysis of this one -- how much shielding do we really need to subdue ionizing radiation from deep space? If you can help with this technical problem, please contact us at artemis@asi.org.
The only problem with putting the windows on the ends away from direct sunlight is that the really boffo view will be toward Earth; and that view periodically will be on a direct line with the Sun. (Think of eclipses and how things line up.) Nevertheless, if we left the north and south directions open, the crew would have a nice view of moon and sky all the time.
Thermal control is another area where we'd need detailed analysis. If the habitat were inside an open-ended garage -- like a quonset hut -- infrared reflection from the shielding and surrounding lunar terrain might be enough to keep warm at night. Picture a half cylinder with no end caps, covered with moon dust.
Access to the habitat and external equipment would really be enhanced by having an open-ended regolith shield. It makes providing a garage for robots much easier, since they can just snuggle up to the habitat at night.
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