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Even in the earliest stages of lunar tourism and settlement, we'll need a passenger bus to shuttle people between the facilities and the spacecraft. Soon after we get there, we'll also want to be able to travel between cities on the moon, as well as getting to the observatories on the limb and the far side. If the ice at the south pole turns out to be a significant resource, the lunar community will surely want to establish a permanent installation there, so that's another place to go.
The moon has a surface area approximately the size of the continent of Africa. We have a lot of territory to cover.
Moonbus Artemis
A pressurized, electrically powered bus will probably be the primary way of getting around on the moon for a long time to come. As with automobiles, buses, and trucks on Earth, nothing else gives us the flexibility we need for transportation.
Railroad
There are a number of concepts for a lunar surface railroad, such as magnetic levitation railways, monorails, and ordinary dual-rail systems. A rail system requires an extensive infrastructure and can only travel on established road beds, but we should keep this option in mind once we've beaten the paths and know where people want to go.
These concepts are discussed in some lengthy in articles you'll find in back issues of Moon Miners' Manifesto. We hope to get those articles on line in the Artemis Data Book soon.
(If you can help with this project, please join the Electronic Communication Technical Committee and volunteer. We need your help! A few back issues of Moon Miners' Manifesto are already on line in section 6.9.3.2 of the Artemis Data Book. You can also get there via http://www.asi.org/mmm/.)
Cable Lifts
One of the more intriguing proposals for transportation is the cable lift, a system like a ski lift with pressurized cars running along overhead cables. Instead of moving the cable, the car would be powered with wheels that run along the cable. This system might have some advantages over rigid rails on the surface: less expensive to build, primary structure (the supporting poles) made from lunar concrete, easier to accommodate changes in temperature.
Rocket Bus
In long run, we'll have some high-speed surface transportation systems. Surface-to-surface rocket travel might be an option, but with a lot of associated development costs, supporting infrastructure, and hazards.
An electromagnetically launched surface-to-surface rocket bus would be more efficient than pure rockets, but only if we're throwing the thing between two launch sites. The bus has to be able to get back home.
The rocket bus concepts have vehicles following a ballistic trajectory from point to point. Near the surface of the moon, that means they're moving at speeds around 2,000 miles per hour. To make them work, we'll have to put a lot of energy into the system at launch. So the passengers will experience very high acceleration at the beginning and end of the flights, and zero g for the cruise phase. This might not be very popular for day-tripping on the moon.
Now, from science fiction, we have some ideas that don't work out too well. In the movie 2001: A Space Odyssey, people used a bus that traveled over the lunar surface, kept aloft by rocket engines. The 2001 bus would be notoriously inefficient because we would be burning rocket fuel continuously just to support the weight of the vehicle. The cost of the fuel and all those rocket engines is a trade-off against the speed of transportation; it's wasteful, but it sure beats crawling along in a rover at 10 miles per hour.
In his science fiction novels, Robert A. Heinlein decribed mass transportation subway systems. One of these was a ballistic flight from point to point beneath the surface of the moon. For long-distance transportation between cities in the moon, this will probably never happen.
On Earth, we use subways only when we have to find a way to get around inside existing cities; as soon as the rail system moves outside the industrialized area, it moves to the surface. Tunneling is expensive, compared to laying out a roadbed on the surface. On the moon, it will be even more difficult because we will be boring through solid rock. So I doubt that we will see long-distance tunnels until the lunar community has developed to the point that it has fully autonomous tunnel-borers sitting around with nothing better to do.
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