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How to build railguns and coilguns, continued...
 
   How to build colonies in space -- we hope...

This turned out to be way off. Today the shuttle costs around $11,000/kg ($5000/lb) to ship payload into low Earth orbit, which is the cheapest of all orbits.

 

Figure: Exterior and interior views of O’Neill space colonies, designed to be four miles in diameter and twenty miles long. Artwork courtesy NASA

But back then, in the early 70s, few researchers outside Fair’s team doubted these cost projections.

O’Neill saw NASA’s launch cost projections, watched men walking the Moon, and he dreamed of building cities in orbit. However, even at $25/lb, it was clear that building them from materials launched from Earth would be staggeringly expensive.

O’Neill’s solution was to ship lunar rock to a manufacturing plant in orbit and convert it into space colony components. Just a matter of engineering, he and his fellow physicists liked to say. (I’m an engineer, and I cringe when I hear people say “just a matter of engineering.”)

To a physicist like O’Neill, he could crunch the physics numbers and the answer seemed obvious. The Earth lies within a deep gravity well, ~9 km/s below low Earth orbit. That means an object on Earth must be speeded up by at least 9 km/s and at the right times and in the right directions to keep it from crashing back to the ground.  To take off from Earth and make a soft landing on the Moon takes over 12 km/s even with the fanciest, time consuming celestial navigation tricks. By contrast, a launcher on the Moon need only accelerate a payload to a little over 2.2 km/s to reach a stable orbit like LaGrangian Libration Point Number Five.

However, rocket launch from the Moon was a no starter. First you had to ship fuel from Earth It would cost too much to ship fuel from Earth. It wasn’t possible to make anything for fuel on the Moon except oxygen, and then only with enormous effort. O’Neill figured out, though, that the Moon had plenty of solar energy. He could use this to power an EM launcher.

Just point the gun on a trajectory to Lagrangian Libration Point Five, located 60 deg ahead of the Moon in its orbit, and a bucket of lunar raw material could coast into the construction shack, slowing almost to a stop thanks to the orbital peculiarities of that location. Just set up a soccer goal and let the incoming material pile up, no rockets needed.

O’Neill went public with his idea in the Aug. 1974 Physics Today magazine. He described cylinders four miles wide by sixteen miles long, gravity simulated by rotation, and inside of them, cities, meadows, lakes, sunshine and clouds. In his Physics Today article, O’Neill concluded that these colonies could be built “with existing technology.”

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       © 2013 Carolyn Meinel