Inflatable habitats

When thinking about the practical design of a Moonbase, the thing that always bothers me is the need for space. Unlike the ISS, a Moonbase would be under the influence of gravity, and so the usage of volume would be very different.

Reasons for needing the extra space apart (having provided it, it's certain that activities would expand to fill it) inflatable modules seem the best way to go about creating it. Why?

The shuttle has a limited volume in its main bay - hence the relatively small size of the ISS modules, but inflatables could provide a much more efficient use of the volume. Consider a balloon and a matchbox. Uninflated, you can fit the balloon inside the matchbox, but when inflated, the volume of the balloon is much, much larger than that of the matchbox. This isn't the best analogy - the anticipated inflation ratio is smaller, and the inflatable module would unfold rather than stretch to its inflated size, but it provides the necessary example.

The original proponents of inflatables for a Moonbase were Kokh et al. [1], who suggested several designs. One of their most important points is that pure inflatable designs are impractical because they require a lot of outfitting - they can have no built in furnishings, and because pure inflatables only come in spherical, cylindrical and toroidical configurations, there is always an inconvenient curved surface underfoot which needs to be decked over for comfort.

Kokh et al. suggest a 'hybrid inflatable', which consists of some hard elements which have inflatable volume expanding between them or out of them. Their favourite design was dubbed the 'Moonbagel': a hard cylinder containing equipment and inflatable walls that expanded out into a torus, the original cylinder filling the 'hole' of the torus.

As meritous as their work was, I personally disagree with the main purpose of their paper, and I will discuss that at a later date.

NASA later took an interest in the Moonbagel design with respect to providing living space for astronauts on the way to and from Mars. Their adaptation, called TransHab, incorporated foot-thick walls for radiation shielding and a central structure fabricated from a lightweight honeycomb material [2].

The Moonbagel concept seems very promising to me, with a few adaptations. I will discuss these tomorrow.

References:

[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

[2] P. Kokh, 'TransHab and the Prehistory of its Architecture', The Lunar Reclamation Society, 1999