“I really want to see a mass driver on the moon that is shooting AI satellites into deep space,” Elon Musk said last week when he announced his plan to go to the moon. “It’s going to be incredibly exciting to see it happen.” He’s right. I want to see it too, although probably we will both be dead before his vision is realized.

The lunar mass driver—essentially a cannon that uses magnetic power to accelerate an object—is a key component to launch the million satellites Musk wants to put in orbit around the Earth. But Musk wasn’t the first person to come up with the idea. Smarter people than him thought about this in the 1970s as the solution to a key problem for human exploration.

Launching spacecraft from Earth is extremely expensive. Every pound lifted from Cape Canaveral to low Earth orbit costs thousands of dollars in fuel, hardware, and operational........

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