Chapter 6 of 10

The Mirror That Still Answers Earth Today

Deploying the Laser Ranging Retroreflector (LRRR) at Tranquility Base

Told in Eagle’s imagined voice · the events are real · source

S69-39961 (16 July 1969) --- The huge, 363-feet tall Apollo 11 (Spacecraft 107/Lunar Module S/Saturn 506) space vehicle is launched from Pad A, Launch Complex 39, Kennedy Space Center (KSC), at 9:32 a.m.
EagleEvery battery on the Moon eventually dies—so I carried one scientific instrument that needed no electricity, no wires, and no radio at all.
NASA
01Forty-five feet from my legs, the astronauts propped up a suitcase-sized panel tilted directly toward Earth, studded with one hundred sunken glass prisms.
Each glass prism was cut into a special 'corner cube'—shaped so that any beam of light hitting it bounces straight back to the exact spot it came from.
02Giant telescopes on Earth began firing brief, powerful laser pulses at Tranquility Base, aiming for a target two hundred forty thousand miles away.
AS11-44-6642 (21 July 1969) --- The Apollo 11 Lunar Module ascent stage, with astronauts Neil A.
EagleTwo and a half seconds after a laser flash left Earth, a handful of reflected light particles arrived back home from our dusty mirror.
NASA/JSC
03Because scientists know the exact speed of light, timing that two-way trip let them measure the distance between Earth and my landing site down to the thickness of a fingernail.
More than half a century later, my batteries are dead—but that mirror beside me is still working right now.
04Decades of laser bounces proved two astonishing truths: the Moon has a fluid core deep inside, and it is slowly spiraling away from Earth by 3.8 centimeters (1.5 inches) every single year.

The big idea

Because the Laser Ranging Retroreflector uses pure geometry (100 glass corner-cube prisms) instead of batteries, astronomers still bounce lasers off it today—revealing that the Moon drifts 3.8 cm farther from Earth every year.

Think about it

Why is the Apollo 11 laser reflector still working more than 55 years later when every other Apollo 11 experiment went silent?

In this chapter: Anodized aluminum panel holding 100 fused-silica corner-cube prisms

Sources: Main record

Machine illustration: AI-made. Photos: NASA Image and Video Library, credited on each picture.

Chapter 6 of 10

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