Laser Ranging Retro-Reflector. Also called LR-3, is an experiment installed on the ALSEP three of the Apollo missions (Apollo 11, 14 and 15), but not part of it, intended to reflect a beam of laser fired from our planet, in order to measure with high accuracy the distance that at a given moment is the Moon .

This experiment has been used for over 35 years and is still active. The reflector of Apollo 15 is three times larger than the other two reflectors previous missions, so this reflector was the target of 75% of the measurements made ​​in the first 25 years of the experiment. The improvement in technology since then has resulted in increased use of the first two reflectors, from different observatories in the world, as the McDonald Observatory ( United States ) and the Côte d'Azur Observatory ( France ).

Some results of this experiment are:

• The orbit of the Moon is moving away from Earth at a rate of 3.8 centimeters per year, due to the tidal land.
• The moon probably has a liquid core.
• It has limited the measurement error of Newton's gravitational constant, so that the force of gravity is very stable.
• The orbit of the moon as far with reflectors is within the limits predicted by the theory of relativity of Einstein .

The two rovers Soviet program automatic Lunokhod Moon also led to similar small mirrors. Were received laser signals bounced off the Lunokhod 1, but contact was lost since 1971, due to the final orientation of the reflector and uncertainty about its location on the Moon. In April 2010, an observatory of the University of California at San Diego, used the images of the Lunar Reconnaissance Orbiter to locate. The April 22, 2010 and subsequent days measured the distance the rover, with success, reaching to within 1 meter. To their surprise, the Lunokhod 1 reflector are reflecting much more light than any of the other reflectors on the Moon. Meanwhile, the retro-reflector of Lunokhod 2 continues bouncing laser signals sent from Earth.

The undeniable presence of laser retroreflectors on the lunar surface has been used as an argument to refute the claims that the Apollo moon landings were fake .

Source: es.wikipedia.org