Taxi Fuel Masses
To fuel taxis for hauling 30 million tourists per year we need 187,500,000 tons of Al and LUNOX. See Taxi Propellant 1 & 2. That's 75,000 flights with 400 passengers per flight from LEEO to the cycler and then from the cycler to L2. With a mass ratio of just 6:1 and an ISP of 285 seconds the taxi uses 1250 tons of Al and LUNOX per flight with an estimated delta V of 5 kps.
Another 75,000 flights are made from L2 to cycler with 400 people returning to Earth and from the cycler when nearing Earth to a taxiport space station in LEEO. A total of 150,000 flights times 1250 tons per flight equals 187,500,000 tons of propellant. The taxis are much lighter than the Moon Shuttles because they only operate in weightless space and they refuel at L2 with propellant sent up from the lunar surface by mass drivers to LLO and hauled over to L2 by NEP freighters that use very little reaction mass so they use less propellant to haul more people.
Moon Shuttle Fuel Masses
The big Moon Shuttles must use about 9234 tons per two way flight and haul only 200 people at a time to get people from the surface to L2 and from L2 to the surface in 12 hours or less. They must make 150,000 roundtrips per year with 200 people returning to Earth from the lunar surface to L2 and 200 new people from L2 to the lunar surface.
The Moon Shuttles will use 1.385 billion tons of monopropellant every year. The total for Taxi and Moon Shuttle propellants will be 1.573 billion tons of propellants every year. We will mine 2.145 billion tons of regolith to provide this. This is less than the approximately 4 billion tons of coal we mine on Earth every year.
Since the Moon has a mass of 7.35E19 tons it would take 46.7 billion years to use the whole Moon or just 46.7 million years to use 0.1% of it! The Moon will not be turned into Swiss cheese as immature thinkers might believe, but how much damage will be done to the natural beauty of the Moon?
Preserving the Moon
If we use Al and LUNOX propulsion for 200 years beginning in the 22nd century before developing more advanced space propulsion systems for large scale space tourism we will need a total of 315 billion tons of monopropellant. If we use aluminum which constitutes 15% of the highland regolith along with silicon at 21% and a corresponding amount of oxygen we will use 73.3% of the regolith mined. See Stochiometry and Rocket Math.
We need to mine 429 billion tons of regolith over this 200 years. We will produce plenty of oxygen for pressurizing lava tubes, iron and ceramics at the same time. With a density of about three times that of water for regolith and hard rock mined we will move about 143 billion cubic meters of material. That's just 143 cubic kilometers or one hundred pits each 10 km. square to a depth of 14 meters over the course of 200 years!
These would not even be noticeable amongst the thousands of lunar craters. We could dig some passes through crater rims for monorail ways and excavate tunnels or enlarge and deepen lava tubes. The pristine environment of the Moon will not be destroyed. We need not destroy lunar mountains. Deep shaft mining and tunneling will preserve the lunar surface and create habitable volume for humans when the old mines are pressurized.
About a fourth of the material mined will not provide rocket fuel but might find other uses; otherwise these mine tailings or slag will be returned to the pits. Leftover material from new pits will be used to fill in old pits. We will not create mounds or pyramids of discarded material that deface the lunar surface nor will we pock mark the Moon with man made craters. Rejected material from underground mines can also be used to fill in the pits. Some old pits could even be domed and turned into habitations.
Robot Workers Wanted
This is a job for nuclear powered replicating robots that can work night and day underground in the vacuum without pay, rest, recreation, air, food or water. The AI machines will need some human supervision but this can be done in real time by teleoperation crews on the Moon. Without robots this task will probably be impossible and unaffordable. I have a great deal of faith in robotics, so I am certain we can conquer the Moon with robots and build enormous industries there. We probably won't use nuclear explosives because this would contaminate tunnels that could someday serve as habitat for humans.
Vast Energy Demanded
Refining regolith will require vast amounts of energy when we consider that it takes about 13,000 kWhrs. to produce a ton of aluminum. If we need about 800 million tons of aluminum ( about half of 1.573 billion tons, without considering Si production for the sake of simplicity) per year we must generate about 10 trillion kilowatt hours! That's a constant load of 1141 GWe. We'd need 5.6 billion square meters of 15% efficient solar panels or a square 75 kilometers on a side or 100 farms 7.5 kilometers on a side. That is not too farfetched for engineers of the future!
The panel farms would be located at various mining and refining sites around the Moon and they would be connected by calcium or actual LN2 cooled super conducting cables to the night side. To keep operations going night and day we'd need twice as many so make it 200 farms about 8 km by 8 km. Since the Moon's surface area is over 38 million square kilometers we would only cover 0.0003 or 0.03% of the Moon's surface with these 200 solar panel farms. Nobody would even notice.
We would also use nuclear fission with uranium and thorium mined from KREEP and helium 3 fusion to generate energy. In the process of magma electrolysis we will generate oxygen. Oxygen will be liquefied easily in shaded radiators. The biggest energy consumer on the Moon will be the rocketfuel industry rather than life support and farming. Despite these enormous masses of propellant for moving millions of people to and from the Moon every year we will barely make a scratch on that beautiful nearest neighbor in space.
Other Fuel Sources
Underground mining could go on for centuries. Most of the tailings would become rocket fuel or material launched into space by mass drivers for space colony and habitat construction, so heaps of material not usable for rocket fuel won't build up even in a thousand years. After extracting aluminum and silicon there will be iron, titanium, magnesium, calcium and trace metals left over. Iron can be burned in sub-orbital "Moon Hoppers" and magnesium could be used for reaction mass in the electric drives of interplanetary ships. Calcium oxide is the active ingredient in cement. Iron reinforced cement might make huge skyscrapers on the Moon. There won't be any slag heaps and the tunnels of the Moon could allow subway travel and habitat for millions of Lunans and visitors. But what if we find another fuel source?
Eventually, huge masses of ice could be mined on the moons of Jupiter; Europa, Callisto and Ganymede. A series of LH2 barges or a "pipeline" from the ice moons could fuel the ships of the solar system. Hydrogen could be combined with silicon to make silane, an excellent rocket fuel. Moon Shuttles would fuel up at L2 with silane made from imported LH2 and mass driver launched lunar silicon and oxygen. Aluminum could be used for construction purposes. Moon Shuttles could even use straight LH2 and NTR (Nuclear Thermal Rocket) propulsion. Moon mining for rocket fuel would end, or be reduced greatly if oxygen was extracted from regolith and sub-surface rock for use in LANTRs (Liquid oxygen Augmented Nuclear Thermal Rockets) to extend hydrogen supplies.
Space Elevators
When space elevators are built from L1 and L2 down to the lunar surface we won't need to mine for monopropellant anymore. Space elevators above Earth will also be able to fling taxis from the upper ends onto trajectories for rendezvous with cyclers without using any propellants at all! Space elevators will be monumental engineering achievements but there is no reason to believe they cannot be built with the super materials based on C60 nanofibers that are predicted in the future. In a matter of centuries we will have space elevators and interplanetary beam riders propelled by particle beams generated by solar powered stations in space and all this mining will become unnecessary except for creation of sub-selene habitat, industry and space colony construction.
Advanced Propulsion
We will have nuclear electric propulsion that consumes very little propellant using high specific mass vapor core reactors (<1 kg./kWe) with MHD like those being researched at INSPI and low mass ceramic turbogenerators to energize electric drives like VASIMR in coming decades but NEP ships will not travel to and from the Moon as this requires to much time spiraling through the Van Allen Belts.
Ships using NEP will leave high orbit for Mars and beyond. NEP could also be used for slow unmanned freighters to deliver cargo to the Moon. Fusion drives will probably be to massive for spacecraft propulsion but "stationary" (they'd actually be in solar orbit and fire opposing beams) massive fusion powerplants in the outer solar system could power beams for beamrider ships. We might even build mammoth solar powered microwave beam stations on Earth and the Moon to propel beamrider ships with huge sails of C60 nanofiber mesh to the Moon and beyond in the 21st century if we can get enough thrust to drive them through the Van Allen Belts fast enough. The beauty of a beamrider ship is that you can make your powerplants located on a planetary surface or in space as huge as you want because the ship doesn't have to drag its powerplant along with it, thus beamriders can be very low mass and efficient.
