Atlantis Astronauts Complete First Hubble Spacewalk

May 14, 2009 -- One down, four to go.

A pair of NASA astronauts completed the first of five spacewalks to repair the Hubble Space Telescope today. The entire mission is considered risky because the astronauts are in an orbit densely littered with space junk.

John Grunsfeld and Andrew Feustel floated out of the shuttle Atlantis at 8:52 a.m. ET and finished their work about seven hours and 20 minutes later. Today's spacewalk was the 19th one to ever service Hubble.

The duo's key accomplishment was installing a new camera in the Hubble Space Telescope, giving it the ability to peer even deeper into the cosmos.

After struggling for a bit with a particularly stubborn bolt, they replaced the 15-year-old Wide Field Planetary Camera 2 with a new piano-sized camera that is significantly more powerful than its predecessor. With the new camera, the telescope will be able to take large-scale, clear and detailed photos over a wide range of colors, NASA said.

"Good job installing it," astronaut Mike Massimino told his colleagues. "Getting Wide Field 3 to unlock the secrets of the universe."

"Let there be light," Grunsfeld said as ground controllers checked the power hookups, the Associated Press reported.

Once the new camera was safely in its new home, the astronauts moved the old camera to the slot on the shuttle that had housed the new one. The old camera will be moved to the Smithsonian.

The pair then replaced a data processing computer responsible for sending the camera's images down to Earth.

The computer's failure last fall, just before a planned mission to Hubble in October, caused a seven-month delay in the mission.

They also installed a mechanism that will allow future vehicles to attach to the telescope.

Tomorrow, astronauts Mike Good and Mike Massimino, the first astronaut to tweet from space, will conduct the second space walk.

The astronauts were told Wednesday night that there was a slight risk of a "conjunction" or collision with debris from an old Chinese weather satellite.

But the 4-inch chunk passed by the shuttle without incident, missing it by several miles Wednesday night. The satellite was intentionally destroyed in January 2007.

Atlantis is in a particularly dangerous orbit 350 miles above Earth, in an area littered with space junk.

"Something the size of a pea could put a hole in the spacecraft," former astronaut Jeffrey Hoffman told "Good Morning America" Wednesday. "They can usually track [pieces of debris] down to two inches. ... What you really worry about are the pieces too small to track, but big enough to do damage."

As his colleagues prepared for the first spacewalk, astronaut Massimino tweeted, "Rendezvous and grapple were great, getting ready for our first spacewalk."

Atlantis made its rendezvous with the Hubble space telescope Wednesday , beginning a week-long effort to replace or repair the aging telescope's vital systems.

With the shuttle's commander, Scott Altman, steering Atlantis, astronaut Megan McArthur reached out and grabbed the Hubble with the ship's robot arm. Then she gently lowered the telescope into the shuttle's cargo bay.

"Houston, Atlantis," Altman called to Mission Control. "Hubble has arrived on Atlantis with the arm."

It was a delicate operation, with the two giant spacecraft flying in formation at 17,200 miles per hour, more than 300 miles above Earth's surface.

"I'm going to have to remind myself to breathe, and take it real slow," McArthur had said in an interview with ABC News before the flight.

Astronaut John Grunsfeld -- an astronomer by training -- took the microphone in the crew cabin a few minutes after the capture.

"I'm looking out the window here, and it's an unbelievably beautiful sight," he said.

Grunsfeld is on his fifth spaceflight, and his third to service the Hubble. He has said he felt strongly about the telescope -- even during the two-year period when NASA thought this mission was too risky to fly, and Grunsfeld, then the agency's chief scientist, had to go along with the decision.