#89 October 1995
Section 188.8.131.52.089.of the Artemis Data Book
This month we return to the points of the first article, what achievements a first outpost on the Moon should strive to achieve, only this time delving into the many "technology" questions of realizing all this. There are lots of choices to make, and, as usual, some of the options will solve problems for the moment but lead nowhere, and other, more challenging options will be pregnant with the future. Enjoy!
Relevant Readings from Back Issues of MMM:
MMM # 1 DEC '86, p 2, "M is for Mole"
MMM # 5 MAY '87, "Weather"
MMM # 25 MAY '89, p 4, "Lava Tubes"
MMM # 37 JUL '90, p 3, "Ramadas"
MMM # 55 MAY '92, p 7, "Moon Roofs"
"Lunar Base Design" by Peter Land, Illinois Institute of Technology, College of Architecture, Chicago, in "Lunar Bases and Space Activities of the 21st Century" pp. 363-73, Ed. Wendel Mendell, Lunar and Planetary Institute, Houston 1984, ISBN 0-942862-02-3
If an Apollo LM [pronounced Lehm] had remained on the Moon, it could not serve as the nucleus for a true lunar outpost. Its thin armor protected from vacuum only, useless against threats potentially just as fatal over the long term. A second much thicker layer of "firmament" is needed.
If human crews are to make extended stays on the Moon, they have the choice of being cavalier about the dangers and flippantly heroic. Or they can make sure their outpost is a true shelter and place of refuge from those characteristic lunar conditions that would inexorably work to do them in:
They can do this by covering their habitat complex with 2-4 meters (yards) of loose regolith soil. The amount or depth of desired cover depends on the longest crews are likely to stay during the lifetime of the outpost. Two meters will do for short durations of a few months. Four meters is better if you might stay the rest of your life.
The direct method is undoubtedly easiest and the most simple, requiring only soil moving equipment which will be needed in any case. If you want to keep the costs and weight of the first return mission down, you might consider this method.
It does have drawbacks! How do you add on later to an already buried complex? Leave the expansion end uncovered? One way, proposed by the University of Houston's Sasakawa International Center for Space Architecture, would be to first fill "sandbags" presumably brought along from Earth, with lunar soil, and then stack these around and over the complex. [See pictures on page 1.] When you need to uncover a section for maintenance or expansion purposes, you just remove the bags in that area and replace them later. An elegant solution.
There is a cost, of course: (a) the bagging equipment, (b) the extra weight of the bags themselves. Eventually such bags might be woven locally of lunar fiberglass - would bringing along the equipment to do all that that be more of an expense than just bringing along ready made bags? If you would break even the next time, or the third time, you brought up an expansion module, would that be worth it? That's a question worth looking into. Certainly, we must always look beyond the needs of the mission of the moment!
But there are other disadvantages of direct shielding, in any form. These are not clear, however, until we look into indirect shielding and learn what fringe benefits it allows.
As a bonus, there is extra radiation-free, UV-free, micrometeorite-free, and flare-proof unpressurized lee "service" space for storing tankage and other routinely needed, frequently tended equipment that does not need to be exposed to the sky. This in turn allows the wearing of lighter weight pressure suits for these kinds of "exterior" housekeeping chores.
The hangar shed makes sense if there is firm, review-proof commitment to phased expansion of the base beyond the original bare minimum habitat structure. For while its construction adds an original base-deployment "delaying" mission or two, the time- and effort-saving dividends down the road are considerable. If our commitment is scaled back to putting a toe in the water, rather than to a wholesale plunge, then, of course, the hangar will be seen as unnecessary.
A hangar can be built in many ways. A pole and "canvas" tent structure can be covered with loose regolith. Alternately, an arched space frame structure can be built, covered with a fabric, then over-filled. A less dead-end, more pregnant approach, at least with a view towards incipient lunar industrialization, would be afforded by brining along molds and a solar concentrator to make sintered arch component blocks out of regolith soil. These could be stacked over an inflatable semi-cylindrical bag. With the completion of an arch section, the bag "slip-form" would be partially deflated, enough to move it over a bit, reinflate it, and support the building of the next arch section. In this way, a little bit of equipment from Earth would allow indefinite expansion of lee space shelter using lunar resources entirely.
This slip-form sintered arch-block approach is well-developed in the paper "Lunar Base Design" by Peter Land of the Illinois Institute of Technology, pages 363-73, in "Lunar Bases and Space Activities of the 21st Century", Ed. W.W. Mendel, Lunar and Planetary Institute, Houston, 1984.
The 'ground' under the arch (the floor of the hangar) can be graded smooth, compacted and sintered to provide a relatively dust-free apron for the sheltered outpost. As we will see in a later article, "site management", dust control, and good housekeeping habits must be in place from the gitgo if our attempt to establish an interface beachhead is not to fall flat on its face. (Inner and Outer "Yard" Managers or yardmasters will be critical job slots.) The hangar approach favors the early adoption and rigorous pursuit of good homesteading habits.
The hangar interior can be naturally lit, during dayspan, by providing intermittent broken-path sun-wells or direct path sun-dows made of bundled optic fibers which double as shielding. Electric lighting for nightspan can be separately suspended from the ceiling or placed above the exterior surface, to use the in-place sun-well or sun-dow light delivery system.
Visual access can be accommodated by broken-path (radiation-proofed) mirrored shafts from the habitat modules underneath through the hangar roof. With proper planning, such ready-access observation ports can be provided ahead of time as the hangar is expanded section by section. Alternately, a pressurized vertical ladder-shaft can lead from habitat below to pressurized observation dome on the hangar roof.
KEY: (1) Space Frame Arch, Fabric Cover; (2) 20 cm or more regolith dust shielding; (3) exposed vacuum, radiation, micro-meteorites, UV, solar flares; (4) protected lee vacuum service area; (5) observation cupola with ladder shaft to habitat space below (7, 8, 9); (6) broken-path solar access via heliostat and fresnel lens diffuser; (10) compacted, sintered hangar apron
Arch-Block Hanger KEY: (1) compacted, sintered hangar apron; (2) "Weather"-Exposed Vacuum; (3) Shielded "Lee" vacuum; (4) self supporting arch made of blocks produced from sintered regolith in simple single shape mold, applied over an Inflatable Slip Form.
Hangars can be open for expansion at just one end or at both ends. The latter ploy makes more sense and provides greater expansion-vector flexibility.
The hangar approach can be called the twin or "Two Firmament Strategy". Sheltering from exposure to the "weather" of the naked lunar skies is handled separately from sheltering from vacuum. An initial "umbrella" firmament is built first and allows a wide range of architectural freedom and plan revision for subsequent base expansion underneath.
In contrast, indirectly shielding individual habitat structures can be called the single, or more aptly, the Joint or Laminated Firmament approach. As usual, impatience quickly proves to have resulted in an unfortunate, option-preempting choice. The Two Firmament approach better embodies the philosophy of the base serving as an "interface" between Moon and Man.
Hangar alternatives If there is no firm commitment to phased expansion, but merely a concession to "leaving the door open" to further expansion, a half-measure would be to directly shield a habitat structure with an attached side or front "carport"/service area. This approach provides the benefits of attached lee vacuum. As to future expansion, the docking port for parking an added module can be included under the carport or under a separate shielding "retaining collar". Obviously, this is a "consolation prize" approach and not the way we should be planning.
Directly Shielded Habitat with Carport/Service Area Shed: KEY: (1) Exposed Vacuum; (2) Sheltered Vacuum of Carport; (4) compacted and sintered floor of carport, part of dust-control strategy.
At the other end, much more ambitious than the hangar, is to place the outpost in a pre-located lavatube. This may involve major up front costs of brining along boring equipment for elevator shafts, and personnel/freight elevators themselves. Lavatubes have great promise, but they seem dauntingly challenging for an initial beachhead establishment venture, posing problems of easy access, floor rubble clearance, and possibly ceiling reinforcement.
In all this discussion, NASA preparation earns a C grade. Johnson SC has looked into both bagged shielding and inflatable structures. And through its space architecture university support programs has furthered studies of lavatube utilization. But much more needs to be done to isolate and identify the most promising alternatives for hangar architecture, weighing heavily those methods that give the biggest and earliest boost to lunar industrialization and use of local resources for further expansion.
NSS could apply some remedial assistance with a sequel to its '99-'89 Space Habitat Design Competition. The design constraints and objectives would have to be clearly defined, looking for maximum use of local materials, minimum need for one-use only import materials, low weight import capital equipment, and adapatability to automated or teleconstruction methods. We'd need a donor/donors of prize incentives sufficient to attract suitable talent. And follow up publication of results (not like last time!).
Apollo left no occupiable structure on the Moon. There is no 'friendly' place to return to, no place where we can go and pick up where we left off.
Contents of this issue of Moon Miners' Manifesto