Numbers

David A. Dietzler, 2007

Some food for thought.  The Moon's mass is 7.35x10E19 metric tons.  If a space colony for 10,000 people amasses 100 million tons, then there is enough mass in just one percent of the Moon to build 7,350,000,000 colonies, enough to house 73.5 trillion people.  That may seem absurd, but consider the asteroids.  There's alot of easily mined mass.  The smaller moons of the outer planets could also be mined.  We could build colonies like Island 3 to house millions of people rather than millions of small ones.  Only AI robot swarms could do all that work.  Then there are the realities of population growth.  At 1% per year, the human population would reach 5.5x10E22 or 55 billion trillion people in 3000 years!!  A growth rate of 0.1% or 0.01% or less might be sustainable for a space civilization.  Chances are that populations will surge then decline and over the long run there could be an overall decline in human numbers rather than an expansion into space.  Then again, our numbers might remain within reason, and we might spread out in space for many reasons other than overpopulation, which is not a realistic reason for expansion, given the fact that we can over run the solar system in a few millenia.

The lunar mass driver launches 10 ton payload modules consisting of metal drums fitted with compressed oxygen cold gas thrusters to a 100 km. high "storage orbit." Hundreds of modules accumulate in storage orbit as mass driver grinds away. When modules are in the right position to rendesvouz with payload collectors in 120 km. high "collector orbit," computers on the ground tracking all payloads order thrusters to fire. A 15 fps maneuver will propell payload modules from storage orbit to collector orbit where another 15 fps "burn" circularizes their orbits and they flow gently into the Payload Collectors which consist of big Kevlar bags and NEP units. The payloads are disassembled, thrusters sent by rocket back to surface for reuse, and the heavy payloads, mostly Moondust, are processed. The metal drums are cannibalized at the processing space station.      Mass drivers on the Moon could launch millions of tons of material into space every year.  Much of this could be used to supply aluminum, magnesium and LUNOX for rocket propellant.  Pure silicon, zone refined in the vacuum and microgravity of space on a massive scale, could be used for solar power satellites. Iron, titanium and aluminum could be used to build space colonies.  Raw regolith and slag could be used for passive colony radiation shields several meters thick.      Although the Moon represents an enormous amount of mass, it is still at the botton of its own gravity well.  If humanity does expand into outer space, an easier source of materials for colony construction exists-asteroids.  We must also consider the martian moonlets-Deimos and Phobos.  These contain over a trillion tons of material that could be used to build numerous space colonies in Mars orbit.  It will be far easier to mine those moonlets than our Earth's Moon.  The martians may prefer to live in spinning colonies with Earth normal gravity, while cultivating the partially terraformed planet below to provide food.  Beyond Mars, the asteroids of the Main Belt and the smaller moons of the outer planets could supply an immense quantity of mass.  The bodies of the Kuiper Belt and Oort Cloud are also of interest. Eventually, we could extract carbon from the atmosphere of Venus, mine the planet Mercury and larger moons, and harvest huge quantities of hydrogen, carbon and nitrogen from the atmospheres of the Gas Giants for structural plastics and other products.  The keys to doing all this are robots.

Cargo Launching to L5 Space Manufacturing Facilites (Space Colonies) ,  Proceedings of the Princeton/AIAA/NASA Conference held May 7-9, 1974, edited by Jerry Grey, published in 1977 by the AIAA, we find an article by Thomas A.Heppenheimer called "Transport of Lunar Material to the Sites of the Colonies" on page 13. describes a lunar transport system.  My comments are below.  I disagree with mass catcher "Venus Fly Trap" system that uses a spurt of gas to slow incoming payloads of regolith and then piping the slurry to rotary pellet launchers to keep the mass catcher on station.  This will waste about a third of the mass launched. It would be better to launch ten ton modules, about the size of a van, with a large mass driver built on the Moon with lunar materials, that have simple hi pressure oxygen cold gas thrusters for accurate navigation into the mouths of mass catchers made of glass fiber cloth spun on the Moon or at the L5 construction shack(s).  Table 3 from the article shows that fast transfers will take from 7.54 days and reach L5 at a velocity of 442 m/s to 15.29 days and 79.2 m/s at L5.  That's 988 mph to 177 mph.   I think that large modules should be equipped with silane/LUNOX retros to slow down to a snail's pace and gently enter the mass catchers without driving them off station or wasting payload to keep them on station. A 350 sec. Isp SiH4/LOX thruster has an exhaust velocity of 3.43 kps.  Thus a mass ratio of 1.137 is needed to decelerate from 442 m/s to zero relative to the mass catcher.  The module, payload and thrusters/retro would amass about 8.79 tons and the silane/LUNOX about 1.2 tons.  This is only 12% of payload mass rather than 33%.  The modules could be converted to living and work habitat at the construction shack(s) and the small rockets cannibalized for their metals. At 79.2 m/s  a mass ratio of only1.023 would be needed, thus, only 0.225 tons or 225 kg would be retro fuel.  The payload modules would be mass produced in a largely robotic factory, loading the modules up with payloads of finished parts, metals, raw regolith and tanks of oxygen and other gases and fueling them would also be done in largely robotic facilities on the Moon.   Millions of tons of materiel must be launched to L5 every year for an aggressive space industrialization program that includes solar power satellites, large telecommunications platforms, orbital manufacturing stations, asteroid deflection systems,  fleets of asteroid mining ships, fleets of nuclear ships to Mars and even military defensive systems that have no offensive potential and therefore do not qualify as weapons in space, but only shields.

ABOVE)  When industry has progressed on the Moon to the point at which mass drivers large enough to launch 12m by 15m conical aerobraking modules carrying alumina and magnesia can be built, it will be possible to supply rocket propellant directly to LEO from the Moon's surface.