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Green Bank telescope to search sky; 'Largest dynamic structure on Earth' growing in West Virginia

THE BALTIMORE SUN

GREEN BANK, W.Va. -- The world's largest machine on dry land seems out of place in the rugged isolation of Deer Creek Valley.

But this patch of scarce flatland, sparsely populated and surrounded by the Allegheny Mountains, is the ideal home for the gleaming white two-acre radio telescope that looms above neighboring farms.

For four decades, this remote Pocahontas County hamlet has been "the center of American radio astronomy," explained Mark McKinnon, deputy site director of the National Radio Astronomy Observatory facility at Green Bank.

Shielded by the mountains from earthly interference such as radio stations, Green Bank's sensitive telescopes have explored distant galaxies by collecting radio waves since 1958. Now construction crews are nearing completion of a colossal new one packed with high-tech improvements. It could let astronomers examine uncharted reaches of the universe, and perhaps alter our conceptions of time and space and creation.

The new Green Bank Telescope (GBT) will be "the largest dynamic structure on Earth," said McKinnon. The only bigger machines are aircraft carriers and similar-sized ocean vessels.

The project has taken more than a decade. It began shortly after the collapse of Green Bank's 26-year-old radio telescope in late 1988. Sen. Robert C. Byrd, a West Virginia Democrat, famous for looking after the home folks, quickly persuaded Congress to appropriate $75 million to begin building a much bigger replacement.

After considerable complications and delay, GBT -- weighing 16 million pounds and as tall as the Washington Monument -- is to be completed this summer.

Having watched the telescope take shape like a monstrous roller-coaster, its neighbors are curious about what it will find, and thankful for the dollars that its construction brought into a hardscrabble community.

The region was initially chosen for an observatory because of "its lack of potential for economic development," said McKinnon.

Pocahontas County is about 100 miles long and 50 miles wide, but only about 8,000 people live there. On the winding mountain roads, some school buses take two hours to reach the high school in Marlinton, the county seat. The Monogahela National Forest covers much of the area.

110 people employed

Steady paychecks are hard to come by. The observatory employs 110 people. Other residents are farmers or loggers. There is mostly seasonal work at the Snowshoe Ski Resort on the far side of Little Mountain.

"You have to string together several jobs to make a living," said Tony Samons, who works as the Green Bank barber and a finish carpenter and preaches to a congregation of about 40 at the Church of God.

"There are three sets of people here," allowed Samons, who charges $4 for a haircut. "First there are the natives. To be a native, your grandpa had to be born here."

Samons, who was born in Kentucky and moved here in 1979, puts himself and many of the observatory people into a second group: longtime residents who have reared families hereabouts, are acquainted with everybody, but aren't "natives."

The third group is made up of "real outsiders" such as transient construction workers or visiting hunters, he said. "The natives call them pilgrims."

It's a stubbornly insular place, where folks mind their own business. "There are still a few people around who would sell you moonshine if you wanted it," said Samons. "But more grow marijuana. They plant it in the national forest or between rows in cornfields."

On Sundays, Green Bank's churchgoers have a choice of the Liberty Presbyterian, Wesley Chapel United Methodist, Hebron Baptist or the Church of God. Wares at the Green Bank General Store range from hand-sewn quilts to crossbows. A homemade ice cream sandwich costs 69 cents, a double-edged ax goes for $45 and a used mandolin will set you back $145. For a fee, the Mountain State Meat Market will turn a hunter's venison into sausage, jerky or cured deer ham.

Green Bank has a clinic, a public library, an elementary school, a post office, a hardware store, a volunteer fire department and rescue squad, a bank, an Oldsmobile dealer, an antique store, a one-chair barber shop and a combination convenience store, gas station and pizza parlor. And now it has a new, world-class GBT -- which stands for "Great Big Telescope," according to local humorists.

The Green Bank Telescope has been described as an ear to the sky. But that's not exactly right.

A radio telescope doesn't "hear" radio signals from outer space any more than a car radio "hears" a Dixie Chicks song broadcast by a country music station. Both have an antenna that collects radio waves, said McKinnon. The car radio converts these waves into sounds. The radio telescope translates them into images or graphs that let astronomers learn about unseen objects in the universe.

Radio signals reaching Earth from faraway galaxies are feeble, often barely discernible. So astronomers are constructing ever-bigger antennae to catch them.

"Just like you can capture more raindrops in a bigger bucket," explained McKinnon. "The GBT has two acres of collecting area. You could build eight houses on it. It will be the largest fully steerable radio telescope in the world."

In addition to its size, the GBT has new technologies aimed at helping astronomers examine the edges of the universe.

"First, there's the offset feed arm," said McKinnon.

In all radio telescopes, the antenna is a parabolic dish that catches the radio signal and focuses it on a receiver.

Earlier models used support arms to hold the receiver over the middle of the dish, but the arms blocked some of the incoming radio waves. The GBT's angled feed arm holds the receiver without interfering with incoming signals. The same design is used on some small home TV satellite dishes.

Another technological advance is the GBT's "active surface," said McKinnon. The surface of its parabolic dish is a mosaic of 2,004 movable aluminum panels mounted on "actuators." As the giant dish is turned and tilted to face the incoming radio waves, computers adjust the actuators to ensure that the surface is absolutely smooth and is focusing the desired signal on the receiver.

The telescope is surrounded by 12 range finders that use lasers to scan the surface of the dish for any irregularities caused by sun or wind. If the hot summer sun has expanded an exposed section of the frame by a fraction of an inch, for instance, the lasers will trigger a corrective movement of the surface panels.

The collected radio signals from space are transmitted via fiber optics from the telescope receiver to a control room and observatory about a mile away. To keep its electronic equipment from tainting the signal from space with their own faint radio waves, this control room is lined with copper wallpaper.

Using diesel engines

Astronomers use old diesel cars and trucks to drive to and from the telescope -- eliminating the interference generated by spark plugs in conventional gas-powered vehicles. The telescope sits on 16 gigantic steel wheels that roll on a circular metal track 210 feet across. The track rests on a reinforced concrete foundation that extends 25 feet below ground to the bedrock.

A gigantic gear raises and lowers the elevation of the huge -- but delicately balanced -- parabolic dish and the offset arm that angles over it. This whole asymmetrical shebang is made of welded steel beams that had to be trucked in over mountain roads.

Despite its enormous size, the GBT is designed to operate more precisely than a quartz watch, said McKinnon.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, a federal agency, and operated under an agreement with Associated Universities Inc., a consortium of academic institutions.

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