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How the L5 Society Tried to Use a Quirk of Physics to Colonize Space

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The 1970s weren't just the dark ages of paisley and bell-bottoms. Some people were trying to rise above their tragic circumstances - and go to space. And they wanted to use a quirk of physics to help them live there.

Right now we're looking to the moon or to Mars to set up a settlement, but it wasn't always so. Forty years ago, a group called the L5 Society was looking for something a little less substantial to set up camp on. The "L" in L5 refers to a Lagrange Point, or Lagrangian Point, which in turn gets its name from Joseph-Louis Lagrange. He realized that in any two-body system, like the moon orbiting the Earth, or the Earth orbiting the sun, there are points of equilibrium. These points take into account three forces.


The first force is the pull of gravity from the central body. In this case, it would be the Earth, tugging at whatever is near it. The second force is still gravity, but the gravity of the orbiting object. Plunk an object down between the moon and the Earth at just the right point, and the two gravitational pulls will balance out. If the two bodies were stationary, that would be that.

But the Earth and moon aren't stationary. They move, and that brings into account centrifugal force, which arises solely due to the motion of the objects. It's the difference between being connected to by a string to a parked car and being connected by a string to a car doing donuts. The car may turn and change direction, but your body will attempt to keep going in the same direction as before. You'll feel something like an outward tug, away from the car. It's the same tug that flattens you against the outside wall of a moving vehicle as it goes around the corner. As the Earth and moon move, objects around them feel the same tug, and that shifts the points of equilibrium slightly. The Lagrangian Points are were all the forces cancel out, and the object will travel along with the two bodies using no power of its own.


It's easy to imagine the Lagrange Point between the Earth and the moon, but there's more than just one point of equilibrium in a two body system. There's also one Lagrange Point to the far side of the Earth, away from the moon. And there's one to the far side of the moon, away from the Earth. These three are Lagrange Points are called L1, L2, and L3. Although you can balance something there, it's hard to do. If the objects shifts slightly further away or closer, it will fall out of equilibrium and needs to correct it course.

But then there are Lagrange Points 4, and 5, known as L4 and L5. These are off to the side of the two objects. If something is placed exactly there, and shifts a little, the gravitational and centrifugal forces will tug it back into place. These areas can be extremely large, allowing for many colonies to be built, at a stationary distance from Earth, and to stay there without any expenditure of fuel.

The L5 Society was put together because people wanted to do exactly that. They wanted to start building at L5, and eventually create space colonies filled with plants, animals, and people. From there, new colonies could be built at different Lagrange points. And not just L4. The Earth and the sun have Lagrange Points as well, as do the sun and all the other planets. Overall, the L5 Society calculated that in about half a century, colonies could be built that housed a population equal to that of Earth.


The L5 idea has some merits. Neil deGrasse Tyson points out in his book, Death By Black Hole, that staying at the Lagrange points requires no fuel for space ships, and so Lagrange points throughout the solar system could be used as fueling stations for interplanetary travel. The points would also be a lot nearer than Mars. But there's something comfortingly substantial about being on an actual planet, instead of an area in space. Would you colonize a Lagrange Point? And if so, what would your address be?

Top Image: NASA

LaGrange Image: NASA

Via: NASA,, Death By Black Hole, Hyperphysics, and The National Space Society.