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Space Shuttle Prepares for Complex Mission - 2002-02-28


The U.S. space shuttle "Columbia" is set to blast into space on a mission to sharpen and extend the vision of the Hubble Space Telescope. The 11-day mission will be the most complex ever for a shuttle crew.

The Hubble Space Telescope, deployed from a shuttle in 1990, has pushed the frontiers of astronomy since astronauts corrected its flawed mirror three years later. The head of space science at the U.S. space agency NASA, Ed Weiler, points to its main accomplishments: Confirming the existence of black holes, helping determine the age of the universe, and looking back to the time when the cosmos was a youthful one billion years old to provide insight into galaxy formation. "This is like a time tunnel through the sky," he says. "It's clear the Hubble has done the science we promised to do and it continues to do even more. But that's not the end of it."

Now, after this fourth shuttle servicing mission, Hubble promises to offer new knowledge about the evolution and future of the universe.

"Our capability now is going to extend a factor of ten," says Wendy Freedman of the Carnegie Observatories in Pasadena, California, who used Hubble to determine the age of the universe at 13 to 14 billion years. "This telescope is going to become even more powerful. It's going to have greater sensitivity, you can see fainter objects, you can see them with much better clarity, higher resolution, and even at colors that were not possible with the Hubble previously."

The tool that will allow this is the telephone booth sized Advanced Camera for Surveys. Astronomers hope it will let them see earlier than one billion years after the creation of the universe, perhaps to the time when stars and galaxies formed. "In the next decades, that's the place where astronomers are going to be looking to see when the first light in the universe is actually happening," says Ms. Freedman.

Installing the new camera during a spacewalk is the shuttle crew's top priority after they place Hubble in Columbia's cargo bay with the shuttle's robot arm.

Another spacewalk is necessary to revive a dormant camera that sees in infrared wavelengths below the visible light spectrum. This requires installing a new refrigeration system to replace one that ran out of nitrogen coolant four years ago. Maintaining an infrared camera is important because infrared light from distant galaxies passes easily through obscuring dust.

Three additional spacewalks are planned to replace a gyroscope that helps point Hubble, add two new solar energy arrays, and install a new controller to distribute power from them.

The power unit replacement is the most risky task because flight directors must shut down the telescope's entire electrical system for the first time, raising the specter of freezing delicate components and ruining them.

But Hubble Program Manager Preston Burch says covers and blankets to protect hardware from the cold will allow them to take the risk. He deems it necessary because of the chance that the old power controller, which has suffered some intermittent problems, could fail before the next repair visit. "We know it's quite serious and we're living on the edge [taking chances], but we don't know with great certainty that in fact that will happen between now and 2010, but it's a pretty catastrophic consequence if it does happen," says Mr. Burch.

This visit to Hubble is the most complex mission in the 21-year space shuttle history. Shuttle program manager Ron Dittemore says it requires more and lengthier spacewalks than ever, five consecutive tightly-scheduled six-and-a-half hour or longer excursions by two alternating pairs of astronauts. "It certainly is going to be challenging and there is not much wiggle room [leeway] in this mission as far as the tasks the telescope project has asked us to complete" says. Mr. Dittemore. "So it's going to be a challenge."