Robert Dicke was an experimental physicist at Princeton University. He liked to build things with his own hands. When NASA began making plans for landing astronauts on the moon, he thought of a scheme that would allow the astronauts to make a serious contribution to science. This would be good for science and also good for the astronauts. The scheme was to measure accurately the distance between two objects, one fixed on Earth and the other fixed on the moon. The measurements would give us improved understanding of the dynamics of the Earth-moon system.

The object on Earth would be a laser emitting very short pulses of light. The object on the moon would be a tray holding a hundred corner-cube glass reflectors. A corner cube is a piece of solid glass cut so as to reflect light efficiently. The corner cubes would reflect the laser pulses back to the laser. The timing of the reflected pulses would measure the distance between the laser and the tray. The astronauts would plant the tray on a firm piece of ground on the moon facing Earth. Because the corner cubes reflect light straight back to its source, the small variations in the orientation of the moon as it moves in its orbit do not disturb the measurement.

Dicke was a practical person. He went to the Edmonds Scientific Company toy store down the road from Princeton and bought a hundred high-quality glass corner-cube reflectors for $25 each. He asked the machine shop at the Princeton University physics department to attach the cubes to a metal tray with a stand to support it. The complete package, including materials and labor, cost a total of $5,000. Then…