Lunar Laser Reflectors

The ongoing lunar laser ranging experiment or apollo landing mirror measures the distance between surfaces of earth and the moon using laser ranging.

Lunar laser reflectors.

The close up here shows the apollo 15 landing site. 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. Five were left at five sites on the moon by three crews of the apollo program and two remote landers of the lunokhod program.

Ringed by footprints sitting in the moondust lies a 2 foot wide panel studded with 100 mirrors pointing at earth. An epic lunar laser experiment is still going strong five decades after the apollo astronauts set it up on the surface. 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 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.

Laser light pulses are transmitted and reflected back to earth and the round trip. For 50 years and counting scientists have been pinging laser pulses off these reflectors to measure the moon earth distance to high precision. The picture at right of the lunokhod rover shows the reflector jutting out in front left. The apollo 15 lunar laser ranging retroreflector lrrr array is one of four such working arrays on the surface of the moon.

Each reflector is 11 cm on a side for a total package 44 cm long and 19 cm across. 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. Retroreflectors are devices which reflect light back to its source. Lunar reflectors have enabled precise measurement of the earth moon distance since 1969.

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. The moonwalking crew of apollo 11 which landed on the moon 50 years ago. The purpose was to calculate distance between earth and the moon.