Friday, March 05, 2004

Applying the Moonbagel

Yesterday I said that the Moonbagel hybrid-inflatable [1] looked like a good design for basing a Moonbase design around. However, as I said, there are a few specifics that I feel should be addressed. Please refer to Kokh et al. so that you know what I'm talking about.

First, dimensions. Consider the floor to ceiling distance of the room you are (probably) seated in now. I expect that you will observe that the ceiling is 8' to 10' above the floor, i.e. 2.5 m to 3 m. This is because that is the amount of vertical space people feel comfortable in, so it would make sense to have that much headroom in a Moonbagel. But remember that the floor of an unmodified Moonbagel would be curved, like the inside of half-pipe. Unless the Moonbagel is decked, it would be difficult to make efficient and comfortable use of the space inside. If the Moonbagel was decked, it would be good place the decking about a third of the way up, so as to get the best trade-off between floorspace and headroom. The lower third of the space available could then be used, for example, for stowage.

But this brings me neatly on to the problem of radiation shielding. In order to get the most efficient possible usage of cargo mass as well as to improve the expansion ratio it would be sensible to have the walls as lightweight as possible. But there is no way that such lightweight walls - for the sake of argument 5 cm thick - would provide sufficient radiation shielding for the Moonbagel's inhabitants. Shielding would have to be provided by a lava tube or by regolith heaped over the inflatable. Assuming there is no accessible lava tube, and that the Moonbagel is 1.5 * 3 = 4.5 m tall, that means digging a hole 2.25 m deep, putting the Moonbagel in and inflating it, and then piling the regolith back over the top. There have been builders at my school recently. It took quite a long time for them to dig a hole 2 m deep, and required some heavy equipment[*].

Back to dimensions. For maximum strength and best unexpanded to expanded volume ratio, a 'slice' of a Moonbagel should be as close to circular as possible. However, the container fills the 'hole' of the torus.

I'm going to need a diagram to be able to elucidate my ideas further. A task for the weekend, maybe.


[*] It's starting to seem inevitable that heavy earthmoving equipment will be needed for the construction of any size of permanent base, so I'm not going to dwell on it.


[1] P. Kokh, D. Armstrong, M.R. Kaehny, and J. Suszynski, 'THE LUNAR "HOSTEL": An Alternate Concept for First Beachhead and Secondary Outposts', The Lunar Reclamation Society, 1991

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