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Campus Currents May 2007: Volume 4, Number 2

Lunokhod Phone Home

One of the greatest successes of the former Soviet space program was a lunar rover called Lunokhod 1—Russian for “moonwalker.” Landing on the moon on November 17, 1970, with a laser reflector, it wandered around the surface for 11 months then mysteriously disappeared—until last spring, when a NASA spacecraft orbiting the moon located the rover and a team headed by UCSD’s Tom Murphy found the exact location of the laser reflector.

An associate professor of physics, Murphy heads a team of scientists that routinely sends pulses of laser light to the moon from a telescope at the Apache Point Observatory in New Mexico (see @UCSD September 2007 issue). The physicists are engaged in a long-term effort to look for deviations of Einstein’s theory of general relativity by measuring the shape of the lunar orbit to within the accuracy of one millimeter, or about the thickness of a paperclip. This is accomplished by timing the reflections of pulses of laser light from reflectors left on the moon by Apollo astronauts and turning the timing measurement into a distance.

Murphy says his team has occasionally looked for the Lunokhod 1 reflector over the last two years, but faced tall odds against finding it until recently.  The breakthrough came last March when NASA’s Lunar Reconnaissance Orbiter obtained images of the landing site. Murphy and company zeroed in on the target coordinates provided by the NASA orbiter, which had earlier captured an image
of the Soviet rover.

Then on April 22, nearly 40 years after the rover and reflector disappeared, Murphy, Russet McMillan of the Apache Point Observatory and UCSD physics graduate student Eric Michelsen, Ph.D. ’07, found the Lunokhod 1 reflector and pinpointed its distance from earth to within one centimeter.

“We got about 2,000 photons from Lunokhod 1 on our first try,” says Murphy, who will be using the new-found Soviet reflector to more accurately establish the distance to the moon. “After almost 40 years of silence, this rover has a lot to say.”

—Kim McDonald