Hubble overhaul won't be easy fix

Perilous mission focuses on extending space telescope's life

February 24, 2002|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

WASHINGTON - Astronomers around the world are holding their breath this week as NASA prepares to launch its most challenging and perilous mission yet to repair and upgrade the 12-year-old Hubble Space Telescope.

In five days of grueling spacewalks, four astronaut-mechanics will work to ensure the future of what is still the world's premier astronomical observatory. They hope to extend a $6 billion mission that has produced thousands of astonishing images and expanded man's understanding of some of the universe's deepest mysteries.

Few will be following their progress more intently than the hundreds of scientists and engineers at the Space Telescope Science Institute in Baltimore, who have invested their careers in Hubble's success.

Astronomer Mario Livio, head of the institute's science division, compared the institute's anticipation of this fourth Hubble servicing mission to childbirth.

"By the time your fourth child is born, yes, you're nervous about this. But you've seen it going well the first three times, so you have a certain confidence things are going to go well," he said.

Even so, he said, as the countdown goes to zero this week, "the level of nervousness will go up."

Seven astronauts are to board the newly refurbished shuttle Columbia for a dawn launch Thursday. In 37 hours of spacewalks beginning March 3, they will:

Replace the last of Hubble's original instruments with a state-of-the art camera that promises a tenfold improvement in the telescope's "discovery potential."

Try to install an experimental refrigeration system for an infrared camera that broke down in 1999 when it ran out of coolant.

Install new, more powerful solar panels and replace a faltering piece of Hubble's pointing system.

And, in their most critical assignment, astronauts will cut all electrical power to the telescope for the first time to replace a circuit box that was never designed to be disconnected in space. No one is sure whether the telescope's instruments will work when the power goes back on.

"Nervous as hell." That's how Ann Kinney, NASA's director of astronomy and physics, described herself as the launch of the fourth Hubble servicing mission neared.

During 12 years in orbit, the 12 1/2 -ton telescope has vastly expanded scientific understanding of the universe. On the short list of its accomplishments are:

Confirmation of the existence of black holes.

Startling images of star birth in the eerie, dusty "towers" of the Eagle Nebula, and stellar death in jewel-like planetary nebulas.

Pictures of some of the most distant objects ever seen - crowds of infant galaxies at the edge of the observable universe in the "Hubble Deep Field."

Detection of evolving solar systems and the first planets found circling stars beyond our sun. More than 70 have been logged.

Hubble's success was never assured, however, and it has always hinged on ingenuity and repairs. In 1993, astronauts had to install corrective optics after scientists discovered, to their horror and embarrassment, that Hubble was launched in 1990 with a misshapen primary mirror.

After more hardware and science upgrades in 1997, astronauts had to return early to Hubble in 1999 to replace six gyroscopes. A series of gyro failures had left the telescope unable to turn and point.

The most critical and difficult task for astronauts on this mission is also a repair. Hubble's Power Control Unit (PCU), an electrical circuit box, has been troubled by an accumulation of failures that threaten the observatory if they grow worse. The unit was not meant to be replaced in space. It is difficult to see, hard to reach and tethered by 36 electrical connectors too small to turn with bulky spacesuit gloves.

In a tedious, seven-hour spacewalk, astronauts John Grunsfeld and Richard Linnehan will first have to disconnect Hubble's batteries. Then, using a wrench in a left-hands-only posture, they'll turn each of the connectors and remove the old PCU.

Until the new PCU is hooked up and the batteries reconnected, Hubble's instruments will be cooling down, and everyone is worried that the temperature changes might cause damage - especially if the repairs take too long.

Cutting the power

Edward Weiler - the associate NASA administrator who, as Hubble program scientist in 1990, had to tell U.S. taxpayers that the telescope was orbiting with a flawed mirror - said cutting the observatory's power "scares me a lot."

Grunsfeld, an astrophysicist and self-described "Hubble hugger," has practiced the task endlessly in a Houston water tank, with one eye closed to mimic the limited visibility. Complete concentration, he said, "displaces any possibility of getting scared." Failure, he says he has been reminded, "is not an option."

The PCU replacement will come during the third of five long spacewalks. The astronauts' first venture outside Columbia will be a 6 1/2 -hour effort to replace Hubble's twin solar panels.

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