Page:Advanced Automation for Space Missions.djvu/294

 scale almost linearly down as low as 1 ton. The equivalents for a scaled-down 2.5-ton HF leach system are 90 kg F2 and 100 kg of H2 and Na. Sodium is about an order of magnitude more abundant than required, and fluorine does not appear to be a limiting factor even if recovery losses and spillages permit only 50% utilization of available stock. The supply of hydrogen, however, is crucial in achieving quantitative materials closure (see below). The 2.5-ton plant described above can output about 91 tons/year, which should be adequate to replicate a 100-ton seed once per year.

The primary use of nitrogen is in making NH3 for the recovery of silica and as N2 and HNO3 for the production of microelectronic chips. The 400 kg N2 given in table 5.13 is sufficient to prepare a maximum of 490 kg NH3, or 1800 kg HNO3</SUB>. (These applications would require a maximum of 86 kg and 29 kg of H, respectively, hence are not seriously hydrogen-limited.) The amount of nitric acid seems more than sufficient, and the NH<SUB>3</SUB> can produce 100 to 1000 kg of silica, which should be adequate with recycling and provided losses can be held to a minimum.

Chlorine appears in the boron- and phosphorus-production cycles - in the former it is consumed and must be recycled; in the latter it is incorporated in a deliquescent compound and should not incur serious losses or require chemical recycling. The preparation of 1 mole of boron requires recycling 0.25 mole of Cl, hence (0.5)(4 kg)(35.45/10.8) = 6.6 kg of chlorine are needed to produce 4 kg of boron. As for the phosphorus cycle, 80 kg Cl produces 125 kg of deliquescent CaCl<SUB>2</SUB> which is capable of absorbing roughly its own weight in water. This should be sufficient with recycling (by simple heating) no more often than once a month on a T = 1 year schedule.

Sulfur is used primarily in the casting subsystem in the fabrication sector (about 600 kg required) and in the manufacture of sulfuric acid. This product is mass-limited about equally by the amounts of S and H available. The 4000 kg of sulfur can be used to prepare 12,000 kg H<SUB>2</SUB>SO<SUB>4</SUB>, and the 200 kg of hydrogen can make up 9800 kg of the acid. Since hydrogen also has many other uses, available S will be underutilized and perhaps 1 or 2 tons of H<SUB>2</SUB>SO<SUB>4</SUB> reasonably can be produced. Is this enough? The main uses of sulfuric acid are in the recovery processes for B, P, F,and Cl, and in the preparation of silanes. The ratio of B:H<SUB>2</SUB>SO<SUB>4</SUB> is about 4:1 moles, so to extract 4 kg B requires 9.1 kg acid. For phosphorus extraction, P:H<SUB>2</SUB>SO<SUB>4</SUB> :: 2:3 moles, so (3/2)(98.1/31)(40 kg) = 190 kg H<SUB>2</SUB>SO<SUB>4</SUB>. For fluorine extraction, F:H<SUB>2</SUB>SO<SUB>4</SUB> :: 2:1 moles, which requires (1/2)(98.1/19)(200 kg) = 516 kg acid. For chlorine extraction, Cl:H<SUB>2</SUB>SO<SUB>4</SUB> :: 2:1 moles, which requires (1/2)(98.1/35.45)(80 kg) = 110 kg H<SUB>2</SUB>SO<SUB>4</SUB>. The quantity of silane needed for microelectronics processing is expected to be minimal, so it appears that adequate supplies of sulfuric acid can be made available with reasonable loss factors to sustain the growth of a fully autonomous LMF on a sulfur budget of about 1500 kg.

The only critical element appears to be hydrogen. This criticality is not especially peculiar to the present design, but rather stems from the relative scarcity of the element in lunar materials and the many chemical processing applications to which it may be put. Any hydrogen-chemistry-based materials processing system will encounter similar difficulties. The 200 kg of available hydrogen could make the maximum quantities of H-bearing compounds listed in table 5.14, although the available hydrogen must be spread ired with lower masses in among these applications as required with lower masses in