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Astronomer Is Flying High Over Peek at Mercury : Science: Kuiper Airborne Observatory, aboard an aged C-141 jet, offers a unique look at Earth's scorched sister planet. Researcher calls experience 'final reward.'


ABOARD THE KUIPER AIRBORNE OBSERVATORY — When the planet Mercury became a bright point of light on her TV screen, Ann Sprague shouted with delight. She had worked more than five years for this moment--eight miles above the Earth aboard a winged telescope.

Sprague, a University of Arizona research astronomer, sat in a spare windowless room that resembles the most spartan of government offices.

The space is aboard an aged C-141 jet, soaring more than 41,000 feet above Nevada. Sticking out of a forward compartment is a one-meter telescope aimed at a battered piece of rock called Mercury, 50 million miles away.

It was the first time ever for NASA's Kuiper Airborne Observatory to focus on Mercury, the Earth's scorched sister planet that orbits closest to the sun.

And it was a career moment for Sprague. For more than a decade she has studied mysterious Mercury using earthbound telescopes. In 1987, she began preparing for this Kuiper mission. Now all that work hangs on the results of a bare 56 minutes of data collection.

"This is the final reward," said Sprague.

Arrayed around the astronomer are engineers, scientists and technicians, all sitting in front of computer monitors or scurrying about making adjustments. The outside world is unseen, remote. Reality lives only in the electronic images--numbers, symbols and squiggly lines--that float across the screens.

The ancient, noisy Kuiper, with its government-green interior, sparse insulation that barely protects against the minus-34 degrees Fahrenheit outside temperature, takes a crew of eight to keep it flying. A sign above a button panel tells it all: "Push Gently. Antique System."

A Commodore 64, an old computer manufactured originally for electronic games, controls and fine-tunes data collection from the telescope.

"It works," said Fred Witteborn, a scientist who directed operation of instruments connected to the telescope.

For more than 10 years, NASA has sent the Kuiper where astronomy telescopes had not gone before, flying at an altitude above 95% of the Earth's atmosphere. From there, the telescope can capture vistas of stars and planets that are blinded on the ground.

And the Kuiper is ready for the surprises of nature. It roamed the Southern Hemisphere to snap an exploding star in 1987, and last summer it collected some of the most detailed views of a comet slamming into Jupiter.

Kuiper's telescope is designed to give rock-solid views despite turbulence that jostles the C-141. Set on air-cushioned supports, the telescope mounting seemed to dance and twist with every dip and rise of the aircraft. And, yet, images on the television monitor had only the faintest jiggle.

"It may look like the telescope is moving, but it's really the airplane," said Carl Gillespie Jr., the mission commander.

For Ann Sprague's research, the Kuiper took off from the Ames Research Center at Moffett Field, Calif., and streaked northward. Clipping a corner of Oregon and turning southeast across Idaho, the telescope collected infrared readings of two stars to calibrate for the target of the day--Mercury.

Two hours into the flight, the Kuiper swept southwest, across Nevada and California and out across the Pacific. The telescope searched and found Mercury, centering a bright point of light in a black box on the monitors.

"Integrating!" exclaimed Diane Wooden, a science team member operating a computer that smoothly meshed with the telescope and started recording data.

Squiggly lines appeared on a printer, each blip a signature of a chemical or mineral on the distant surface of Mercury. That was it--just wavy lines on graph paper. But for Sprague and other astronomers it spoke of billions of years of history.

"It's beautiful! Wonderful!" said Sprague.

More than 600 measurements flowed into the computer during the mission and the astronomer will spend months analyzing the results.

At first cut, she said, there was both disappointment and triumph.

"I thought we'd get into textbooks by identifying all the rock types on Mercury," she said. "But I don't think that will happen."

Instead, Sprague said, the preliminary analysis is consistent for feldspar, but found little trace of several of the other common planet-building minerals. This means Mercury's geology is far different from the moon, which it closely resembles. The finding also supports the idea that Mercury has a thin crust atop an iron core, unlike Earth.

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