WASHINGTON -- The Hubble Space Telescope is in trouble, NASA reported yesterday.
Three of its six gyroscopes have failed and the fourth could give out shortly, interrupting the flow of priceless astronomical data gathered by the Hubble from objects in space as near as the planets and as far as remote corners of the universe.
Daniel S. Goldin, administrator of the National Aeronautics and Space Administration, said yesterday that he will decide by the weekend whether to launch a space shuttle on an "emergency mission" to rescue the telescope this fall.
"What we're concerned about is losing the scientific data stream for a year or so," Goldin told the House Space subcommittee.
"The Hubble is an irreplaceable resource," said David Lekrone, chief scientist for the Hubble team.
Launched in April 1990, Hubble underwent a repair mission in December 1993 to fix a faulty mirror. New, more powerful instruments were installed by astronauts on another shuttle flight in February 1997.
The latest problem was discovered a few weeks ago, said NASA spokesman Douglas Isbell.
One of the six redundant gyroscopes failed in 1997, another last year and a third last month. Corrosion in wiring connecting the gyroscopes threatens the survival of a fourth. The remaining two are 6 or more years old.
"We need a minimum of three gyroscopes to operate," Lekrone explained.
It takes three such rapidly spinning devices to establish Hubble's precise position and orientation in three-dimensional space so that it can point accurately at targets trillions of miles away from Earth, he said.
The telescope itself is not in danger, Lekrone said.
"If it dropped below three [gyroscopes], the spacecraft would put itself in `safe mode,' sit there and wait for us to come up on the next service mission."
But an interruption in the flow of scientific data would be a "long-term loss," he said.
The telescope is halfway through its planned 20-year life, and every usable minute of observing time is taken.
"We have hundreds of science programs scheduled each year," Lekrone said. "Hubble has a finite life. A month lost is a month lost."
Astronauts would have to make two or three space walks to replace the faulty gyroscopes, Isbell said.
While they are up there, they might also install a new computer and data recorder.
Former astronaut Story Musgrave, who made two space walks in 1993 to repair Hubble's original blurry mirror, said replacing the gyroscopes should not be difficult.
"It's very doable," he said. "It's basically a friendly job."
The next regular service mission in the fall of next year would take up a new camera and replace the telescope's aging solar panels.
Hubble is supposed to continue working until 2010, by which time a larger, more powerful space telescope should be in orbit.