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some miracle, the western nations were to divvy up with everyone else, the Second Report can't challenge one feature of THE LIMITS TO GROWTH: no matter how wildly successful we are in imposing Zero-Growth and population control, in 400 years the game will be over. We will have run out of non-renewable resources. Mankind will have no choice but to give up high-energy civilization and return to some kind of pastoral society.
    Surely this is not a desirable goal? There may be those who dream of the simple life (and a lesser number who will actually choose to live it), but surely only a madman would impose it on everyone else without dire necessity? If there is any alternative, must we not take it?
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    There are alternatives. They aren't even very expensive compared to the MATTP plan. Take, for example, the detailed plans of Princeton professor Gerard K. O'Neill.
    Details of what have come to be called O'Neill Colonies were first widely published in the September 1974 issue of Physics Today. The plan has been modified somewhat since that time, most recently by a week-long NASA sponsored conference of some of the biggest names in space exploration, but the basic concept remains the same: building self-sustaining colonies in space. O'Neill colonies have a major advantage: they are not only self-sustaining, but will be capable of building more colonies without further investment from Earth. Moreover, they will be able to make some important contributions to Earth's economy.
    There's been a great deal of excitement in the science community, and of course among science fiction fans, although oddly enough most SF writers haven't put much about O'Neill colonies into print. I haven't because I assumed others would, and I was waiting for new details. Certainly much of the SF community is aware of the O'Neill concept. "Life In Space" is now a regular program item at science fiction conventions.
    The basic O'Neill plan is for colonies able to support from 10 to 50 thousand people each. They will be located in the L4 and L5 points of the Earth-Moon system. Since not all readers will know what that means, and the location is important to the economics of the concept, let me take a moment to explain Trojan Points.
    The equations of gravitational attraction are so complex that we can't really predict where planets, satellites, moons, etc., will be after long periods of time. Given high-speed computers we can make approximations, but we can't precisely solve problems involving three or more bodies except in special cases. A long time ago LaGrange discovered one of those special cases, namely? that when a system consists of three objects, one extremely massive with respect to the rest, and a third very small with respect to the other two, there are five points of stability: that is, things that get to those points tend to say there. These are often called "LaGrangian Points," and designated by the numbers LI, L2, . . . L5. They are illustrated in Figure 8.
    Of the five, three are not really stable; that is, if an object is perturbed out of LI, L2, or L3, it won't tend to return. The other two, L4 and L5, are dynamically stable, and it takes a special effort to get out of those locations. Left to themselves things put into points L4 and L5 will be there forever.
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    Figure 8

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    Nothing is left to itself, of course: there are more than three bodies in the solar system. Even so, satellites placed at those points would be stable over geological eras.
    Points L4 and L5 are named Trojan Points because in the Sol-Jupiter system these points are occupied by a number of asteroids named after Trojan War heroes. The Trojans trail Jupiter, while the Greeks lead. Unfortunately the custom of naming the Eastern group for Greeks and the Western for Trojans wasn't established before one asteroid in each cluster was named for the wrong class of hero; thus there's a Trojan spy among the Greeks, and vice-versa.
    Because of the perturbing