Page:Advanced Automation for Space Missions.djvu/303

 plaster fuses at 1720 K - very near the melting point of basalt - and loses its water of crystallization around 475 K, it cannot be used to make basalt castings. Iron molds cast from refractory templates are required; they may be reused or recycled as necessary.

Another principal application for basalt is as an insulating fiber. Spun basalt threads can be used to wrap electrical conductors to provide insulation, woven to produce "mineral fabrics" as filler to strengthen cements, shock-absorbing resilient packing material, filters and strainers for materials processing, or as thermal insulation or to prevent cold welding of metals (Green, unpublished Summer Study document, 1980). The technology for producing spun basalt products (Kopecky and Voldan, 1965; Subramanian and Kuang-Huah, 1979), basalt wool, and drawn basalt fibers (Subramanian et al., 1975) is well established commercially and customarily involves extrusion or simple mechanical pulling from a melt (see sec. 4.2 2).

Ho and Sobon (1979) have suggested a design for a fiberglass production plant for the lunar surface using a solar furnace and materials obtained from lunar soil (anorthite, silica, alumina, magnesia, and lime). The entire production facility has a mass of 111 metric tons and a power consumption of 1.88 MW, and produces 9100 metric tons of spun fiberglass per year. Assuming linear scaling, the production for the replicating LMF of even as much as 10 tons of fiberglass thread would require a production plant of mass 122 kg and a power consumption of 2.1 kW (a 2-m solar collector dish).

A small number of LMF parts will also be made of iron (from refractory molds) and refractory cements (carved directly from ceramic clay by the casting robot) in order to take advantage of the special properties of these substances. The total mass of such items is expected to be relatively low. Used refractory molds may be fed to the ball mill and recycled if necessary.

5F.4 Laser Machining and Finishing

The plaster casting parts manufacturing technique was chosen in part because of its ability to produce ready to use "as-cast" components. Thus, it is expected that the majority of parts will require little reworking, machining, or finishing. A small fraction, perhaps 10%, of all lunar SRS parts may require more extensive machining. A laser machining system was selected for this function in the LMF. The characteristic circumference of the typical part is 3.14(0.1/3000)1/3 or about 10 cm. If surface articulations cause an increase by a factor of ten in the total average path length that must be machined, then the mean operating speed of the laser system must be (106 parts/year)(10% machinables)(0.1 m/part)(10 m path/m circum.)(1 year/8722 hr) = 11.5 m/hr. Table 5.16 compares the performances of several different types of lasers, and table 5.17 gives specific performance parameters for high-power gas lasers used in industry for welding (butt, lap, comer, and edge) and for cutting. Inspection of these values suggests that a 5-10-kW continuous-wave (CW) carbon dioxide laser should be able to weld and cut "typical parts" with characteristic dimensions up to 3 cm at the required throughput rate.

aMaximum thickness given here is for Type 304 stainless steel.