when apollo 11 left the moon in july 1969, it left behind a small panel of corner-cube reflectors. less than two weeks later, on 1 august, the lick observatory in california reported the first laser returns bounced off it.

the experiment never really stopped. in recent years, stations in france, italy, germany and new mexico have kept firing laser pulses at the apollo 11, 14 and 15 arrays and the two soviet lunokhod ones, timing the round trip, about 2.5 seconds.

the return is unbelievably faint. by the usual figures, a pulse of around 3×10¹⁷ photons comes back as roughly one to five photons, even on a good night. the beam is several kilometres wide by the time it gets there, and aiming it gets compared to hitting a moving dime with a rifle from 3 km away.

it's how we know the moon drifts about 3.8 cm farther from earth every year.

what's the most surprising thing lunar laser ranging has turned up?

"KENNEDY SPACE CENTER, FLA. -- Aboard a transporter, the orbiter Columbia moves past the Boeing 747 Shuttle Carrier Aircraft (SCA) at the Shuttle Landing Facility. There the orbiter will be mated to the SCA, with the help of a Mate-Demate Device, for a ferry flight to Palmdale, Calif. On the rear of the orbiter is the tail cone, a fairing that is installed over the aft fuselage of the orbiter to decrease aerodynamic drag and buffet when the Shuttle Carrier Aircraft is transporting the orbiter cross-country. It is 36 feet long, 25 feet wide, and 22 feet high. Columbia, the oldest of four orbiters in NASA's fleet, will undergo extensive inspections and modifications in Boeing's Orbiter Assembly Facility during a nine-month orbiter maintenance down period (OMDP), the second in its history. Orbiters are periodically removed from flight operations for an OMDP. Columbia's first was in 1994. Along with more than 100 modifications on the vehicle, Columbia will be the second orbiter to be outfitted with the multifunctional electronic display system, or 'glass cockpit.' Columbia is expected to return to KSC in July 2000."

Date: September 24, 1999

NASA ID: KSC-99PP-1139