Fuel mining costs must be considered. Since there's about a gallon of water (as ice) per cubic yard of regolith (?) or about 4 kg., we must mine 250 cubic yards or about 500-750 tons of moondust to get one metric ton of water. So we need 132,000 cubic yards (about 300 kilotons) with LH2/LOX rockets and 82,000 cu.yds. (200 ktons) with silane/LOX rockets to fuel just one taxi flight. If we did that much mining for water that was to be recycled forever it would be worth the cost; but for one rocket flight and out into the vacuum forever with water as precious as gold? We aren't afraid of big mining jobs with only one ton of 3He per 100 million tons of moondust, but just a few tons of 3He can run a small country for a year! The cost/benefit ratio must be considered. With Al/LUNOX rockets we need 1250 tons of propellant per taxi flight or 660 tons of Al. That much Al can come from 4400 tons or 1700 cubic yards of anorthositic highland regolith with 15% Al in it Compare that to 82,000-132,000 cubic yards or 200,000-300,000 tons of icy moondust.
The next objection is going to be,"well, you don't have to mine nearly as much moondust to get Al+LUNOX, but you have to use so much more energy to process the metals and oxygen out of it when you just have to roast the water out in a solar furnace..." I can only say yes, but then you have to electrolyze the water and liquefy the gases, and you have to mine in the coldest parts of the Moon...etc. etc. |
