Still going after 40 years: the lunar laser ranging experiment

SPACE.com : The Lunar Laser Ranging Experiment is the only moon investigation to continuously operate since the Apollo 11 mission .The experiment studies the Earth-Moon system and beams the data to labs around the world, including NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif.Data from the ranging experiment has been used to learn—among other things—that the moon has a fluid core and is moving away from the Earth, and that Einstein’s Theory of Relativity is accurate.The instrument itself, called a lunar laser ranging reflector, was originally intended to accurately calculate the distance between the Earth and moon by measuring the round-trip time of a laser fired from Earth to a reflector on the instrument.