Lunar Laser Reflector

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.

Lunar laser reflector.

The close up here shows the apollo 15 landing site. Laser light pulses are transmitted and reflected back to earth and the round trip. Retroreflectors are devices which reflect light back to its source. An epic lunar laser experiment is still going strong five decades after the apollo astronauts set it up on the surface.

The experiment consists of an instrument called the lunar laser ranging reflector designed to reflect pulses of laser light fired from the earth. The mcdonald observatory in texas usa the apache point observatory new mexico usa and the observatoire de la côte d azur france are the only currently operational llr sites. Five were left at five sites on the moon by three crews of the apollo program and two remote landers of the lunokhod program. 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.

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 idea was to determine the round trip travel time of a laser pulse from the earth to the moon and back again thereby calculating the distance between the two bodies to unprecedented accuracy. Each reflector is 11 cm on a side for a total package 44 cm long and 19 cm across. The ongoing lunar laser ranging experiment or apollo landing mirror measures the distance between surfaces of earth and the moon using laser ranging.

The picture at right of the lunokhod rover shows the reflector jutting out in front left. The latter has. 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. Ilrs observatories carrying out lunar laser ranging llr to retro reflector arrays on the surface of the moon.

Ringed by footprints sitting in the moondust lies a 2 foot wide panel studded with 100 mirrors pointing at earth. The apollo 15 lunar laser ranging retroreflector lrrr array is one of four such working arrays on the surface of the moon.