Why NASA put the first big colony at L5

Why did NASA’s 1977 study put the first big habitat at L5 instead of on the Moon? Because it wanted a place that stayed in a stable Earth-Moon position, got sunlight, and sat where moving material cost less propellant than fighting a deep gravity well.^[1]

1) Libration-point logic: the study says L4 and L5 are stable, while L1, L2, and L3 are unstable and would need much more station-keeping, so L5 was the low-maintenance choice.^[1]

2) Continuous sunlight: in free space the colony could use full sunshine, while a lunar surface site would only get the Sun directly part of the time. That matters because the design tied agriculture and power to steady solar input.^[1]

3) Logistics to Moon and GEO: the study chose L5 because it was reasonably accessible from both Earth and Moon, and because lunar materials could be shipped there to build solar power stations for geosynchronous orbit.^[1]

4) Eclipse avoidance and trade-offs: locations near Earth or the Moon were rejected because eclipses would cut off light and energy. L2 was chosen for the lunar mass stream, but L5 stayed the habitat site; the study also says lunar orbit, Earth or Moon orbits, and other points were considered and set aside.^[1]