| MadSci Network: Engineering |
Hello, David: I think the idea of the Gravity Train is fascinating! http://digg.com/general_sciences/Isaac_Newton_s_gravity_powered_train_throu A tunnel, driven in a straight line (a chord of the planet's surface) into which one drops a capsule. Gravity acclerates the capsule, then slows it to arrive at the opposite end of the tunnel. The mathmatics work out that one can travel anywhere to anywhere, even right through the center of the planet, always taking 42 minutes, 12 seconds for the trip. http://www.math.purdue.edu/~eremenko/dvi/gravsol.pdf The size of the planet drops out of the equation, so the time is the same for any planet made of the same materials as the Earth. The Moon is actually a bit lighter: http://www.windows.ucar.edu/tour/link=/earth/moon/lunar_interior_structure. The technology to construct a gravity train exists, in the form of Tunnel Boring Machines (TBM) http://en.wikipedia.org/wiki/Tunnel_boring_machine They were invented in their current form back in the '80's, used first in Europe and to drive the Channel Tunnel. http://www.theotherside.co.uk/tm-heritage/background/tunnel.htm From an Engineering standpoint, it wouldn't be too hard to point one in the right direction and just start drilling. And of course there would be no problems evacuating the air from a tunnel on an airless body. Even in the Moon, though, there would be difficulties with faults, varying types and densities of rock, plastic flow of "solid" rock under tremendous pressure, and so forth. Energy to drive the TBM would have to be generated -- football-sized fields of solar cells, or nuclear power plants. Emergency rescue would be a problem, also, although not insurmountable. The real drawback would be that there would have to be a reason to go from one end of the tunnel to the other. Enough people would have to be living on the Moon to make the trip worthwhile. It will be a few hundred years before the Moon is populated enough to justify such a big project. And while operating costs would be low (no expense for power!) the initial construction costs would still be very high. The chunnel is 31 miles long, and cost 10 billion pounds -- a gravity tunnel going longer and deeper would cost much more. Still, I wonder what the trip would be like, especially one right through the core, where the passengers would be weightless for the entire trip!
Try the links in the MadSci Library for more information on Engineering.