America is headed for the moon again, and Maryland scientists will be in the vanguard of the effort. NASA has chosen research teams from the University of Maryland, College Park and the Goddard Space Flight Center in Greenbelt to work on ideas for upgrading instruments that Apollo crews left behind in the lunar dust.
Two other scientific proposals from area institutions - a small radio telescope array from the Naval Research Laboratory in Washington, and a Goddard instrument to measure X-rays were also selected. The four were picked from among 75 ideas submitted for funds to begin concept development.
"It's exquisite technology to do field science on another world, and [astronauts] haven't had an opportunity to do that since I was a boy," said Alan Stern, NASA's assistant administrator for science. Stern, who approved the selections, was 11 when astronauts first landed on the moon in 1969.
The new equipment would be placed on the lunar surface when astronauts return, after an absence of 50 years, under the timetable set by President Bush's "Vision for Space Exploration."
Maryland's scientists and engineers have a long record of success in space exploration, with central roles in manned flights, orbiting observatories including the Hubble Space Telescope, and in robotic missions to Mercury, Pluto, comets and asteroids.
Concept studies such as these four are inexpensive - no more than $100,000 each - and preliminary. "In this case it's to get scientific groups thinking seriously about doing astrophysics - those things you can do better from the surface of the moon than from free-flying spacecraft," Stern said.
Teams based at UM College Park and Goddard each have different ideas for improving the way lasers are used to measure the distance from Earth to the moon. Either would provide new insights into the moon's structure and natural history, and the fundamental nature of gravity itself. But it will be up to NASA to choose between them or combine the best ideas of both.
The laser "retroreflectors" placed on the moon during three Apollo missions in 1969 and 1971 are still used by physicists to calculate the distance from the Earth to the moon, which ranges from roughly 225,600 to 252,000 miles.
The accuracy is equal to the width of a paper clip. But as good as that is, researchers say it's no longer good enough.
Experts say that like vinyl LPs and air-cooled VW engines, the 1960s-era lunar reflectors just can't match the 21st-century performance that modern equipment on Earth already demands.
If they want to test Einstein's theories about the nature of gravity, for example - and perhaps usher in an entirely new understanding of matter and energy, from the galactic scale to the subatomic- they need even more precise measurements of the moon's orbit.
This "lunar ranging," as it's known, is old hat to Douglas G. Currie, a UM physics professor and principal investigator on one winning proposal.
Currie, 71, was on the Maryland team that developed the original Apollo lunar laser reflectors and participated in their first tests. They immediately reduced uncertainties about the true distance to the moon from a kilometer to about a foot. "It opened up a whole variety of science," he said.
To "range the moon," scientists fire short bursts of laser light through a telescope to the Apollo reflectors, which bounce it back to the telescope. The speed of light is well known, so by measuring precisely how long it takes the light to return - roughly 2.5 seconds - scientists can compute an exact distance.
With repeated shots, they can determine more precisely the moon's orbit around the Earth.
They have already confirmed that the moon is slipping away from the Earth at a rate of 1 1/2 inches a year - a consequence of ocean tides that are slowing the Earth's rotation and speeding up the moon's orbit.
They have measured the rebound of continents from the weight of Ice Age glaciers. And they've clocked the drift of the Earth's continental plates - at the speed of growing fingernails.
From small variations in the moon's rotation, scientists have deduced that the moon is not just a cold ball of rock as they long believed, but probably has a fluid, molten core.
Along with Currie, astrophysicist Stephen M. Merkowitz, who is principal investigator on Goddard's laser ranging proposal, would like to test Einstein's theories.
The so-called "equivalence principle" holds that gravity is the same for all objects. This means a feather and a hammer dropped simultaneously in a vacuum will fall at the same rate - an experiment Apollo astronauts repeated on the moon and found to be correct.
Improved lunar ranging could reveal violations of the equivalence principle. Finding one would constitute a huge breakthrough in fundamental physics. More than proving that Einstein was wrong, the discovery might lead to theories that finally unify gravitational physics with quantum physics - the bizarre behavior of subatomic particles.
Today's understanding "has got to be wrong in some way. We just don't know how yet," Merkowitz said.
Lunar ranging is not as simple as it sounds. Even highly concentrated laser beams spread out over distance. A half-inch-wide laser beam on Earth spreads out and is several kilometers wide by the time it reaches the moon, delivering a tiny fraction of its light to the reflector. And it dims even more as it spreads out on the journey back to Earth.
"You're lucky if you get one photon back per laser firing," said Merkowitz.
To detect any returning light at all, scientists need a powerful laser, a big telescope and filters that can separate the laser's precise frequency from the gusher of sunlight reflected from the moon. In the United States, only the McDonald Observatory near Fort Davis, Texas, and the Apache Point Observatory south of Cloudcroft, N.M., can do the job.
The Apollo reflectors have their own problems. Crews from Apollo 11 and Apollo 14 set two up in 1969 and 1971. Each held clusters of 100 so-called "corner cubes," with optical properties that reflect light from any angle directly back to its source.
Apollo 15 astronauts deployed a bigger set late in 1971. With 300 reflectors, it's the easiest mirror to use and the favorite of today's scientists.
But after all these years, the Apollo reflectors are dusty, and the moon wobbles like a top, limiting the corner-cube clusters' precision.
The University of Maryland proposal would deploy four to eight individual corner cubes. But they would be bigger - each four inches across - and spaced 10 yards apart so scientists on the ground can identify each one's reflection, boosting precision.
Five-hundred-degree temperature swings on the moon also distort the reflectors' glass, so Currie's team is trying to account for that problem in their calculations. The heat and cold can even cause soil expansion that will move the reflectors a few fractions of a millimeter.
"I want to get rid of that ground motion," Currie said. So astronauts will have to drill holes and set the reflectors' supports deep enough to be unaffected by surface temperatures.
The eventual cost of the experiment? "I think in the domain of $10 million," Currie said.
The team Goddard's Merkowitz assembled is considering an "active" or "transponder" laser system. It would include a small telescope to more easily detect the laser pulse arriving from Earth and its own laser to fire back.
"All you have to do is record the time sent and the time you received a pulse," Merkowitz said. "You can process that to calculate the range." The precision could be astonishing, he said, perhaps as exact as four thousandths of an inch in the Earth-moon distance.
A transponder station would enable less-powerful ground lasers to range the moon, cutting costs on the ground and allowing more observatories to participate, Merkowitz said.
An ideal spot for measuring the moon's wobble would be at either pole, also a prime location for a manned base since it would have constant sunlight for solar power. The cost? "On the order of $30 million to $50 million," he said.
There's also the future to consider. "Part of the 'Vision for Space Exploration' is not just to return to the moon, but to use it for a test bed for going to Mars," Merkowitz said.
The Red Planet is too far away for passive laser ranging. But a laser transponder could do the job, he said, offering more precise navigation across the solar system.
frank.roylance@baltsun.com