Hubble's last fix-it mission is also its riskiest

The grand telescope's fifth and final repair expedition will involve five spacewalks and extended exposure in a debris-filled region. NASA will take extra precautions to protect the shuttle crew.

After 19 years of service, during which time it has provided the most eye-popping images ever of galaxies, nebulae and, most recently, of a planet orbiting an alien star, the Hubble Space Telescope is suffering the pains of old age. It's unsteady, with only half its gyroscopes working, and several of its key science instruments are broken.

To restore the ailing telescope to its former glory, NASA on Monday is set to launch the fifth and final repair mission to the orbiting telescope.

The Hubble mission is unusually risky, even by space travel standards, involving five spacewalks and extended time in the debris-riddled layer above Earth, where even a small collision with space junk could render the shuttle useless. The vulnerability of the shuttle fleet to small bits of flotsam was tragically demonstrated by the destruction of the shuttle Columbia in 2003, which was hit during liftoff by a piece of foam insulation from the external fuel tank. The searing heat of reentry widened the hole on the left wing and destroyed the orbiter as it attempted to land in Florida.

Top NASA officials say they will do everything they can to ensure the safety of the crew of the shuttle Atlantis, including flying the orbiter upside down and backward to minimize the danger of being struck by space debris and having a second shuttle on the launchpad in case a rescue mission must be mounted.

"This is going to be an extremely challenging mission," said shuttle pilot Greg Johnson.

Big Bang quest

If successful, the mission will leave the telescope with six new gyroscopes, six fully charged batteries, and four repaired or replaced cameras and spectrographs, including the workhorse wide-field camera No. 2 that was responsible for some of Hubble's most dramatic images. The repairs will keep Hubble functioning at peak efficiency at least through 2014, by which time the next-generation James Webb telescope is scheduled to take its place.

This suite of upgraded instruments will enable the refurbished telescope to look back in time to the very beginnings of the universe.

"This will be our first realistic chance of detecting the first stars and galaxies that formed" right after the Big Bang, almost 14 billion years ago, said UCLA astronomer Matthew Malkan, whose team will be among the first users of the refurbished instrument.

Malkan estimates that the reborn Hubble will be 100 times as powerful as it was when it was carried to orbit in April 1990.

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