


Mike Eckardt
The use of inflatable habitats may not be as simple as Mr. Mook indicated in his study.
Accepting the structural properties of polyester film (25,000 psi yield), a wall or floor section composed of two layers of 12.5 mil film, separated by polystyrene (negligible strength), will accept a structural bending moment of 625 ftlb/ft. If we assume a floor loading of 10 lb/ft^{2} (Earthly design standards are 100 lb/ft^{2} +), the maximum span we could bridge with this material would be about 22 feet. This maximum can only be attained if we stress our materials to the yield point, which is very poor engineering practice.
Similarly, the bubble structure of the habitat will be subject not only to internal pressure loading, but also to a significant dead load resulting from the cover of lunar soil over the structure. If we assume a weight of 150 lb/ft^{3} (Earth) for typical regolith, a twofoot cover over the dome would weight approximately 50 lb/ft^{2}. As described, the Inflatable would fail.
A modified design of the inflatable bubble could be used, however, that would avoid these flaws, as well as the problems that Mr. Bennett mentioned in his critique. To support a bending moment of 15,000 ftlbs
The loading on floor elements is much less than the bubble. Here, we could get by with about 4,500 ftlb in bending (2), which can be easily supported by a double layer structure as described above, except with a flange spacing of only 12".
The empty space provided by this method of construction is typically used on Earth for utility services. Presumably similar uses could be made of it in a lunar habitat.
Using the above method of construction, the habitat weights that Mr. Mook provided would be changed to the following:
3.75 psi 14.7 psi  Shell 3,187 lb 12,750 lb (3) Air 2,225 lb 8,900 lb Flooring 3,000 lb 3,000 lb Vertical Boom 280 lb 280 lb Horizontal Boom 150 lb 150 lb 3 Airlock Doors 1,440 lb 1,440 lb Airlock Tube 360 lb 360 lb  SUBTOTAL 10,642 lb 26,880 lb
While these figures are substantially higher than those Mr. Mook provided, they probably represent a more stucturally sound habitat. Other factors not included in this summary are materials required to make the habitant livable (utilities, dividing walls, etc.).
Mb = 50lb/ft^{2} * 30ft * 30ft / 2  50lb/ft^{2} * 30ft * 20ft / 2 (approx. triangular section) = 7,500 ftlb * 2 (S.F.) = 15,000 ftlb
Mf = 20lb/ft * 30ft * 30ft / 4 = 4,500 ftlb
NOTE: Neither calculation has considered shear loading on structural member.

