For any assembly or structure, whether an isolated bunker or a self sustaining space colony, to be able to function perpetually, the ability to manufacture any of the parts necessary to maintain, or expand, the structure is an obvious necessity. Conventional metal working techniques, consisting of forming, cutting, casting or welding present extreme difficulties in size and complexity that would be difficult to integrate into a self sustaining structure.
Forming requires heavy high powered machinery to press metals into their final desired shapes. Cutting procedures, such as milling and lathing, also require large, heavy, complex machinery, but also waste tremendous amounts of material as large bulk shapes are cut away emerging the final part. Casting metal parts requires a complex mold construction and preparation procedures, not only does a negative mold of the final part need to be constructed, but the mold needs to be prepared, usually by coating in ceramic slurries, before the molten metal is applied. Unless thousands of parts are required, the molds are a waste of energy, resources, and effort. Joining is a flexible process, and usually achieved by welding or brazing and works by melting metal between two fixed parts in order to join them — but the fixed parts present the same manufacturing problems.
Ideally then, in any self sustaining structure, metal parts should be constructed only in the final desired shape but without the need of a mold and very limited need for cutting or joining. In a salient progressive step toward this necessary goal, NASA demonstrates the innovative Electron Beam Free Forming Fabrication (http://www.aeronautics.nasa.gov/electron_beam.htm) Process. A rapid metal fabrication process essentially it “prints” a complex three dimensional object by feeding a molten wire through a computer controlled gun, building the part, layer by layer, and adding metal only where you desire it. It requires no molds and little or no tooling, and material properties are similar to other forming techniques. The complexity of the part is limited only by the imagination of the programmer and the dexterity of the wire feed and heating device.
According to NASA materials research engineer Karen Taminger, who is involved in developing the EBF3 process, extensive simulations and modeling by NASA of long duration space flights found no discernable pattern to the types of parts which failed, but the mass of the failed parts remained remarkably consistent throughout the studies done. This is a favorable finding to in-situe parts manufacturing and because of this the EBF³ team at NASA has been developing a desktop version. Taminger writes:
“Electron beam freeform fabrication (EBF³) is a cross-cutting technology for producing structural metal parts…The promise of this technology extends far beyond its applicability to low-cost manufacturing and aircraft structural designs. EBF³ could provide a way for astronauts to fabricate structural spare parts and new tools aboard the International Space Station or on the surface of the moon or Mars”
NASA’s Langley group working on the EBF3 process took their prototype desktop model for a ride on the microgravity simulating NASA flight and found the process works just fine even in micro gravity, or even against gravity.
The advantages this system offers are significant. Near net shape parts can be manufactured, significantly reducing scrap parts. Unitized parts can be made — instead of multiple parts that need riveting or bolting, final complex integral structures can be made. An entire spacecraft frame could be ‘printed’ in one sitting. The process also creates minimal waste products and is highly energy and feed stock efficient, critical to self sustaining structures. Metals can be placed only where they are desired and the material and chemistry properties can be tailored through the structure. The technical seminar features a structure with a smooth transitional gradient from one alloy to another. Also, structures can be designed specifically for their intended purposes, without needing to be tailored to manufacturing process, for example, stiffening ridges can be curvilinear, in response to the applied forces, instead of typical grid patterns which facilitate easy conventional manufacturing techniques. Manufactures, such as Sciaky Inc, (http://www.sciaky.com/64.html) are all ready jumping on the process
In combination with similar 3D part ‘printing’ innovations in plastics and other materials, the required complexity for sustaining all the mechanical and structural components of a self sustaining structure is plummeting drastically. Isolated structures could survive on a feed stock of scrap that is perpetually recycled as worn parts are replaced by free form manufacturing and the old ones melted to make new feed stock. Space colonies could combine such manufacturing technologies and scrap feedstock with resource collection creating a viable minimal volume and energy consuming system that could perpetually repair the structure – or even build more. Technologies like these show that the atomic level control that nanotechnology manufacturing proposals offer are not necessary to create self sustaining structure, and that with minor developments of modern technology, self sustaining structures could be built and operated successfully.