| Reality Check: He3 vs. SPS David A. Dietzler, 2007 To mine 33 tons of helium 3 every year, enough to power the USA for a year, we will need 1000 of Kulckinski's Mark 3 miners or 10,000 tons of them (1). The value of this helium 3 will be about $100 billion based on energy content of about 19MWyrs./kg.. To build 1000 SPS rated at 10 GWe each (enough to supply about 20% of our world's total energy use in 2050) amassing 125,000 tons apiece we will need 125 milion tons of steel, aluminum, glass foam, glass-glass composites, titanium, aluminum, calcium and silicon. A reasonable guess is that about 250 million tons of regolith must be mined to get these materials. If we want to get the job done in 50 years and reduce fossil fuel burning simultaneously, with the hope that global energy demand and population growth levels off in the mid-21st century, we will need to mine five million tons of regolith every year. A fleet of about 100 mining machines that can mine 1000 tons and hour, with down time for maintanence, could mine this much. The challlenge appears when we must smelt all this material to metals and ceramics, maunfacture everything from steel tubes to solar panels, and generate enough power to do this work and launch the metals etc. to L5 by mass driver. Substantial industrial development must occur on the Moon for decades preceeding this level of activity. To make about three million tons of steel every year we will need to produce 16,500 tons a day during dayspan. We will need 165 DRI "blast" furnaces capable of 100 tons every 24 hours during day span when solar energy is abundant. One hundred tons of iron is 13 cubic meters or a box 7.7 feet on a side. Each DRI furnace of this size will amass several thousand tons, mostly in the form of large basalt, ceramic and stone blocks. We can envision steel jacketed furnaces with refractory linings and inert gas cooling, but the stone furnaces, seemingly primitive, will be cheap to build and act as massive heat sinks that don't need cooling and they won't get so hot that they crack or melt either. While the best place to put the first Moon base is on the Mare Frigoris coast, the biggest industrial center may be the Marius Hills where over 200 low volcanic domes exist and perhaps pockets of trapped volcanic gas rich in carbon monoxide and other gases, even water and hydrogen sulfide. Volcanic glasses have small amounts of chlorine on their surfaces. Perhaps significant amounts of chlorine gas exist in the hypothetical volcanic gas pockets of the Marius Hills. Tubular steel will be the main material for circular SPS frames. The frame will be prestressed with steel or titianium cables so that when the SPS rotates slowly the tension on the frame comes down nearly to zero. The cables will help "pull' the swedged and joined tubes together. Thin film silicon solar panels with aluminum backings doped with Al and P toasted out of KREEP will be mounted on the frame. Tubular steel will be used because it is easy to make in large qtys. compared to other metals and has a higher strength to weight ratio than pure aluminum since we won't have copper or lithium to alloy aluminum and make high strength alloys. Steel is easier to weld also. Aluminum must be welded with tungsten electrode hi temp arcs because it conducts heat away from the weld zone so rapidly. At least we won't need a shield gas in the vacuum. SPS will use amorphous silicon panels unless new space manufacturing processes are developed to make more efficient monocrystalline panels. Solar thermal SPS might be more efficient but more complex and have higher maintenance requirments. Experience in the future will decide. Apparently, helium 3 mining is a smaller job than SPS construction, but a respectable job nonetheless. It could reap profits to finance SPS construction and these power sats could extend the Moon's helium 3 supplies for centuries as well as supply cheap electricity, in our vision of things. So helium 3 mining will come first even though solar panel technology is here and now. We must achieve helium 3 fusion soon. Fusion will also provide waste heat for building steam loops of great value to northern cities in the cold seasons. In the tropical zones plain electricity will be deisred for air conditioning. The use of he3 and SPS keeps us from putting all our eggs in one basket should something happen to cut off either supply of energy. There will also be extensive ground based energy systems like winds and roof top solar as well as conservation that will become very popular as fossil fuel prices rise in the 21st century as they have been doing for decades. |
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| 1) http://www.nasa-academy.org/soffen/travelgrant/gadja.pdf and http://fti.neep.wisc.edu/pdf/wcsar9311-2.pdf |