Finding a lost Soviet Union lunar rover on the moon was like finding the proverbial needle in a haystack, said the Chattanooga native who led the team that found the vehicle last month.
Dr. Tom Murphy, 40, associate professor of physics at the University of California, San Diego, said after NASA’s Lunar Reconnaissance Orbiter took an image of the area where the Lunokhod 1 rover reportedly was left, his team found it on the first try on April 22, using a laser on a 3.5-meter diameter telescope at the Apache Point Observatory in New Mexico.
“With 10 seconds of firing (the laser),” he said, “we knew we had it.”
It’s not the rover itself that’s so important, Dr. Murphy said, but its reflector and its position on the surface of the moon.
Because the roughly 18- by 8-inch reflector is farther toward the “edge” of the visible moon, he said, it’s the most useful of the five reflectors on the lunar surface in measuring the wobble, or orbital distance and motion, of the moon.
measuring the wobble
Bobby Thompson, of Chickamauga, Ga., a former astronomy teacher at the University of Tennessee at Chattanooga and former head of Jones Observatory, said the nearly 5 percent north and south wobble in the moon allows some 59 percent of its surface to be seen.
Three of the other four reflectors were left by the United States on the Apollo 11, 14 and 15 missions between 1969 and 1971, and the fourth is on the Soviet rover Lunokhod 2, left there by the unmanned Luna 21 mission in 1973.
Measuring the wobble, said Dr. Murphy, a Georgia Tech and Cal Tech graduate, provides critical information to scientists who want to test the moon’s gravitational forces.
“Einstein’s general relativity theory is our current best description,” he said. “No experiment has shown it to be wrong, but physicists feel general relatively is not the last word in gravity.”
Before the reflectors, Mr. Thompson said, far less could be learned about the moon’s mass, its distance from Earth, and its expansion and contraction.
Trying to measure such distances, he said, was like “trying to shoot a duck from a merry-go-round.”
Tom Patty, director of the Challenger Learning Center at the UTC, said the fact that equipment sent to the moon nearly 40 years still can be helpful is a testament to science.
Today, he said, “the technology has just become so infinitely more effective and efficient that it amazes me.”
LOST FOR DECADES
The unmanned Soviet space mission Luna 17 landed on the moon in late 1970 and released Lunokhod 1, which maintained contact until Sept. 14, 1971. Its exact location, with the critical reflector — a series of glass prisms that can bounce back the light from a directed laser beam — had been unknown since.
Dr. Murphy said scientists “knew roughly” where the rover was, but said the system used to locate it was demanding in terms of coordinates and required more searching than was practical.
Plus, he said, time on the Apache Point Observatory telescope is highly competitive. What time they had on the telescope was used to measure orbital distance and motion with the other four reflectors on the moon.
“There are a lot of challenges in doing it well, doing it right,” Dr. Murphy said.
BACK TO THE MOON?Whether the United States should return to the moon in the near future as former President George W. Bush suggested (but money for which was eliminated from the 2011 budget by President Obama) is a “tough call,” Dr. Tom Murphy said. For him personally, he said, “it would be great” because the lunar reflectors used by his University of California, San Diego, team for calculations are old and degrading, which limit their precision. But as a citizen, he said, “I would have to ask what are we getting out of it as a nation?” He said he’s not sure it would be as inspirational to a younger generation as many believe because “you can’t squeeze the same lemon twice.”
In doing lunar laser ranging, he said, a sharp pulse of laser light is sent from the telescope to a reflector on the moon’s surface. With the knowledge of the speed of light and how long it should take for the light to hit and return from the reflector, certain calculations can be made.
Dr. Murphy said he does not have to be at the Apache Point Observatory to conduct the experiments.
Indeed, he said he has done them from his parents’ home in Chattanooga while visiting.
He wasn’t even in New Mexico when the Lunokhod rover was found, he said, but was remotely “eavesdropping” on colleague Russet McMillan, who was at the controls.
“At first,” said Dr. Murphy, “we puzzled over (the returned light) and said, “Gee, is that a signal?'”
Eventually, he said, they realized it was and that they had found the elusive rover that had been undetectable for nearly 40 years.