National Geographic : 1972 Feb
around. Finally, at a depth of five and a half feet, he is forced to stop. He inserts the heat probe as far as he can. He fares no better on a second hole and gives up for the moment; time is running out for this EVA. Before returning to the LM, Scott sets out a fancy kind of mirror, a laser ranging retro reflector (known commonly as LR 3 ), and aims it toward earth. To the southeast, about 600 miles away, stands a similar mirror left by the Apollo 11 crew; some 670 miles to the southwest is a third, set up by the men of Apollo 14. The three serve a common pur pose: to bounce laser signals back to earth. The round-trip time tells scientists the pre cise distance between earth and moon at any given moment (233,850 miles on average, 248 surface to surface) to an accuracy of a few inches. By triangulation, it will also make possible measurements on earth itself ac curate within ten inches or so.* But the Hadley device offers a huge ad vantage over the others; instead of 100 fused silica reflectors, it presents 300, and thus can bounce back three times as much light. Safely back in the LM, after more than six hours on the surface, the men take off their suits and helmets and notice an odd odor like gunpowder, which they attribute to the lunar soil they have tracked into the cabin. And they complain that their fingers are *See "The Flight of Apollo 11: 'One Giant Leap for Mankind,'" by Kenneth F. Weaver, NATIONAL GEO GRAPHIC, December 1969.