Astronauts Ready For Repair Trip to Battered Hubble

The great telescope in space has an antenna with a hole in it the size of a .22-caliber bullet. One of the telescope's main cameras has died. So has an instrument called a spectrograph. Three of six stabilizing gyros are kaput. A data router failed, and a backup had to take over. The telescope is getting slower about latching onto guide stars. The batteries are running down. And the shiny exterior has been torn up by countless collisions with tiny particles.

Yet, despite the battering and the ravages of old age, the Hubble Space Telescope is still 500 million times as sensitive as the human eye, and astronomers say its best days may yet be ahead. That depends on what happens in coming days when astronauts aboard the space shuttle Atlantis attempt to give the orbiting observatory new instruments, new batteries and a new lease on life.

This will be the fifth and final servicing mission to the telescope and, unquestionably, the trickiest. The servicing had originally been scheduled for 2004, but NASA canceled the mission after the Columbia disaster heightened concerns about shuttle astronauts' safety. With the Hubble doomed to expire in orbit as its gyros failed, schoolchildren across the country donated their lunch money to prod NASA to reconsider. In 2006, NASA decided to reinstate the mission.

The launch is scheduled for this afternoon, and there will be a second shuttle ready to rocket into space should anything go wrong with Atlantis. The telescope orbits about 350 miles above Earth, far above the potential refuge of the international space station. Any serious damage to Atlantis during launch would require that astronauts abandon the shuttle in orbit and be rescued by the crew in the second shuttle.

Once the astronauts aboard Atlantis inspect their spacecraft for signs of damage, they will rendezvous with the telescope and drag it with a robotic arm into the shuttle's payload bay. Then come five spacewalks. The astronauts have a long checklist, including the installation of a new camera and a new spectrograph.

Some of the upgrades are relatively straightforward and modular: yank out old part, put in new. But they're big parts: The "fine guidance sensors" sound delicate but weigh as much as a grand piano back on Earth (though in microgravity, not so much).

What's different this time is that the astronauts will also open up some instruments and root around inside, doing Geek Squad-like repairs while wearing bulky spacesuits and traveling around the planet at 17,000 mph.

At one point, astronaut John Grunsfeld, making his third trip to the Hubble, will have to use a power tool to remove dozens of screws to get inside the Advanced Camera for Surveys. The screws must be rounded so that they don't become projectiles that could damage the telescope. Grunsfeld will also have to replace four circuit cards, all of which will be around a corner and out of sight.

Although the focus will be on the spacewalking astronauts, engineers at Goddard Space Flight Center in Greenbelt will be busy running through a 550-page checklist as they give the telescope commands. Among other things, the Goddard staff will shut down power to parts of the telescope to prevent electrical arcing that might puncture an astronaut's glove.

"We have this choreographed almost down to the minute of what we want the crew to do. It's this really fine ballet," said Keith Walyus, the servicing mission operations manager at Goddard.

So, is he anxious about the mission?

"This is great!" Walyus answered. "We've been training for this for seven years. We can't wait for this to happen."