Lunar Laser Reflectors

The reflectors are too small to be seen from earth so even when the beam is correctly aligned in the telescope actually hitting a lunar reflector is quite challenging.

Lunar laser reflectors.

Five were left at five sites on the moon by three crews of the apollo program and two remote landers of the lunokhod program. At the moon s surface the beam is a few kilometers or miles wide and scientists liken the task of properly aiming the beam to using a rifle to hit a moving dime 3 2 kilometers. Science experiments laser ranging retroreflector the laser ranging retroreflector experiment was deployed on apollo 11 14 and 15. The lunar laser ranging retroreflector array apollo 11 astronauts buzz aldrin and neil armstrong put it there on july 21 1969 about an hour before the end of their final moonwalk.

Lunokhod 1 was successfully ranged during its maneuvering phase but then was not seen for almost 40 years until our project with the help of the lunar reconnaissance. The ongoing lunar laser ranging experiment or apollo landing mirror measures the distance between surfaces of earth and the moon using laser ranging. The apollo 15 lunar laser ranging retroreflector lrrr array is one of four such working arrays on the surface of the moon. Retroreflectors are devices which reflect light back to its source.

Lunar reflectors have enabled precise measurement of the earth moon distance since 1969. It consists of a series of corner cube reflectors which are a special type of mirror with the property of always reflecting an incoming light beam back in the direction it came from. Laser light pulses are transmitted and reflected back to earth and the round trip. The purpose was to calculate distance between earth and the moon.

Part of the apollo program specifically the apollo 11 14 and 15 missions involved something called the lunar laser ranging experiment where astronauts set up retroreflectors that can reflect a laser beam sent from earth. An epic lunar laser experiment is still going strong five decades after the apollo astronauts set it up on the surface. The moonwalking crew of apollo 11 which landed on the moon 50 years ago. The picture at right of the lunokhod rover shows the reflector jutting out in front left.

Each reflector is 11 cm on a side for a total package 44 cm long and 19 cm across. Lasers at observatories on earth are aimed at retroreflectors planted on the moon during the apollo program 11 14 and 15 and the two lunokhod missions. For the physics community the biggest payoff from the apollo science program has come from the reflector arrays which are part of the lunar laser ranging llr experiment.