For three decades, these measurements have been gathered at the McDonald Observatory. The lunar ranging station there is one of just two in the world in regular operation. The other is in France.
Today, four observers work in what looks like a storage shed set in scrub oaks and pines a short walk from the observatory's graceful domes. "We look ugly, but we produce really good data," says Jerry Wiant, the station's project engineer, a 29-year veteran.
Shooting laser beams at the Apollo sites and catching their reflection is still an art, Wiant says. An observer sits for hours, amid computers and the whir of fans. He watches the telescope's video monitor as the moon's gray surface (nearly featureless in this close-up) glides by.
The view is "not very rewarding," Wiant concedes. Guided by computer, the telescope finally settles on a crater close to one of the Apollo landing sites. From here, the observer moves the telescope manually, relying on memory and instinct to find the invisible reflector. "We're pointing at something we can't see," Wiant says.
The operator rolls a track ball to place a cursor over the spot where he thinks the reflector ought to be. Then he clicks a mouse and staccato bursts of laser light -- 10 pulses per second -- stream up to the moon. The green beam, 30 inches wide when it leaves, widens to 6 miles by the time it reaches the moon. For every 20,000 units of light that leave Texas, only 1 finds its way back.
If no light comes back, the operator nudges his cursor across the lunar surface a bit and fires again. "There's a bell that rings when they get a return," Faller says. "They need some reward."
The station also performs laser ranging to 24 military, scientific and navigational satellites fitted with corner cube mirrors, helping to precisely track their orbits.
The work costs NASA $37,000 a month, down 12 percent since a budget cut in May. Faller says the hugely expensive International Space Station, which he calls "a WPA project for the aerospace industry," is draining money from small space science programs like this one. (The Works Progress Administration was a Depression-era government make-work program.)
Peter J. Shelus, a research scientist and astronomer at McDonald, says the Apollo-era lunar ranging station could become a NASA budget casualty.
"There are only two operating lunar laser-ranging stations in the world. And we are both at risk of going down completely," he says. If data collection stops, gravitational models -- and navigation across the solar system -- will become unreliable in five to seven years.
Smarter spacecraft could compensate for the lost data. But that costs money, too, he says. And "you're going to miss out on lunar science. There's no free lunch."
Pub Date: 7/20/99
