Apollo Laser Ranger Retro-Reflector

Side view of a white pallet with raised 100 lens laser reflector, training unit, Apollo 11.

The Laser Ranging Retroreflector experiment consists of a series of corner-cube mirrors designed to reflect an incoming light beam back to its source. Astronauts deployed this experiment on the lunar surface during the Apollo 11, 14, and 15 missions. From Earth, laser beams are aimed through large telescopes at the Retroreflector on the lunar surface, which then reflects the laser beam back to Earth. The Retroreflector provides precise measurements of the distance between the Earth and the Moon, the Moon’s orbit, and the rate at which the Moon is receding from the Earth.