Sitting at his home computer on the evening of 22 April, Tom Murphy, an astrophysicist at the University of California, San Diego, logged into an observation session 1200 kilometers away, at Apache Point Observatory. From a pine-dotted ridge above the White Sands Missile Range, Russet McMillan, the on-site specialist, aimed the New Mexico observatory's telescope at a small patch of dust near the edge of the moon's face. Then, at Murphy's go-ahead, she fired a stream of laser pulses into the night sky.
The pulses—20 per second—shot toward the moon and, after little more than a second, bathed the lunar dust patch in a pool of green light. Another second passed. Then Murphy saw a blip in the data on his screen. It suggested that an unusually large number of photons had returned from the moon and were being recorded by the telescope's photodiode.
At first, Murphy thought the blip might just be an artifact of the instrumentation, a common disturbance caused by turning the detector on and off. But no matter how McMillan tweaked the instruments, the signal kept showing up. By the next morning after analyzing the data, he was sure the blip represented something much more significant: contact with the first robot to roam a surface beyond Earth. Until NASA's Lunar Reconnaissance Orbiter snapped photographs of the robot's tracks earlier that month, no one had been able to locate the Soviet rover Lunokhod 1 for nearly four decades.
But the discovery has turned out to be more than a just a fun bit of space archaeology. Now that Murphy has confirmed the location of Lunokhod 1, he plans on using the aging rover to help measure the moon's movements and test theories of gravity with the greatest precision to date.
In November 1970, more than a year after the United States' Apollo 11 mission, Soviet engineers sent Lunokhod 1 to the moon aboard a probe named Luna 17. Powered by solar cells and equipped with radio antennas, cameras, and a dust-sampling scooper, Lunokhod 1 had the appearance of an otherworldly creature. "It looked like a metallic washtub with a dome top and wire-mesh wheels," says Cathleen Lewis, a curator at the National Air and Space Museum in Washington, D.C.
The rover, whose name translates to "moon walker," rolled down a ramp onto the moon, "thus taking the first giant step for robotkind on another celestial body," Time magazine reported the following week. Soviet engineers "made much of the fact that they were pioneering robotic exploration as opposed to human exploration," Lewis says. (Due to the success of its manned programs, NASA wouldn't have its own remote-controlled rover until Sojourner rolled onto Mars in 1996.) For 11 months, Lunokhold 1 toured the moon, sampling lunar soil and beaming thousands of images back to Earth.
But each lunar nightfall, which happens about every 29 Earth days, the sun-powered rover shut down. "That kind of thermal cycling is really tough on electrical and mechanical parts," Murphy says. "So every morning when they'd get a new sunrise on the moon, [Lunokhod's operators would] hold their breath and hope that the thing would power up and start working again. And month after month it did. Then one day, some component somewhere failed, and Lunokhod just didn't wake up."