Astronauts float out on first Hubble spacewalk

Two astronauts from the US space shuttle Atlantis Thursday began the first of five ambitious spacewalks to overhaul the Hubble space telescope and extend its working life.

The spacewalk by astronauts John Grunsfeld and Drew Feustel got under way at 1252 GMT and was scheduled to last for six to seven hours.

"We got the boys all dressed up and ready to go," said astronaut Mike Massimino, who assisted the two men with preparations.

Massimino and Mike Good will alternate spacewalks with Grunsfeld and Feustel over the five days.

"It's a great Hubble day," said Grunsfeld, a 50-year-old astronomer who is on his third mission to Hubble. Feustel, a 43-year-old geologist, is flying in space for the first time.

The spacewalks follow after the seven-strong Atlantis crew on Wednesday plucked Hubble from orbit, maneuvering it into the shuttle's cargo bay for a long overdue maintenance.

Officials believe the overhaul will extend Hubble's operations by at least five years, long enough to finish the development and launch a more powerful successor, the James Webb Space Telescope.

During Thursday's spacewalk, the two men will replace the Wide Field Planetary Camera-2, a 16-year-old workhorse imager, with the updated Wide Field Camera-3.

The new camera is designed to look deeper into the universe, perhaps as far back as some 500 to 600 million years before the Big Bang, with observations in the ultraviolet and infrared regions of the electromagnetic spectrum.

Grunsfeld and Feustel will also replace the telescope's failing science computer. The Science Instrument Command and Data Handling system experienced a partial electronic failure in late September.

Time permitting, the two astronauts will also install a soft capture mechanism for future vehicles to attach to the telescopes, NASA said.

As their final scheduled task, they will install three "latch-over-center" kits allowing them to open and close the telescope doors faster during the third spacewalk, which will also be performed by Grunsfeld and Feustel.

When the overhaul is complete, Hubble should have new batteries and gyroscopes, rejuvenating the electrical and pointing systems.

On Wednesday, astronaut Megan McArthur grappled the 13.2-meter (43-foot) telescope with the shuttle's robot arm, after Atlantis commander Scott Altman maneuvered his spacecraft within 10 meters (35 feet) of the scientific icon.

"Houston, Atlantis, Hubble has arrived on board," Altman radioed Mission Control.

The two spacecraft were 560 kilometers (350 miles) above Australia at the time of capture. After the grapple, McArthur carefully hoisted the observatory toward a rotating work platform in the rear of the shuttle's cargo bay.

The big telescope will remain anchored to the platform for the next six days.

Wednesday's rendezvous operation grew more challenging when a communications problem kept the Atlantis crew from seeing the results of positioning commands they transmitted to the telescope.

Hubble's Maryland command center monitored the commands instead, relaying the results to the astronauts.

Altman flew the final kilometer of the encounter manually, gingerly easing Atlantis closer to the telescope from below with the assistance of shuttle pilot Greg Johnson and Mike Good.

The astronauts later scanned the Hubble's exterior with cameras on the robot arm, finding it in good shape despite signs of weathering from ultraviolet radiation and impacts from space debris.

"It's an unbelievably beautiful sight," gushed Grunsfeld. "Amazingly, the exterior of Hubble, an old man of 19 years in space, still looks in terrific shape."

Shuttle astronauts had not seen or worked on Hubble since March 2002.

Hubble, a cooperative project between NASA and the European Space Agency, has been refurbished four times since its launch in 1990.