A pair of spacewalking astronauts on Thursday outfitted the Hubble Space Telescope with a new camera that will allow astronomers to turn their gaze closer to the birth of the universe.

Clad in bulky pressurized spacesuits, five-time shuttle flier John Grunsfeld, 50, and rookie partner Andrew Feustel, 43, floated outside the shuttle Atlantis for a spacewalk that lasted over 7 hours.

The 11-day mission is the U.S. space agency's last chance to service the telescope - which has vastly expanded scientists' knowledge of the universe - before NASA ends the shuttle program in 2010. It is NASA's fifth and final servicing call to Hubble, which was put into space in 1990.

NASA hopes the improvements will keep Hubble operational until at least 2014 so it can work in tandem with its projected replacement, the James Webb Space Telescope.

Tethered to the shuttle's robotic arm, Feustel struggled with a bolt on the old camera for more than an hour, finally using a wrench and old-fashioned elbow grease to pry it loose.

It's been in there for 16 years -- and it didn't want to come out, Grunsfeld said.

Installing the new wide field camera was among NASA's highest priorities, and will allow Hubble to capture images of objects formed as early as 500 million years after the birth of the universe.

Grunsfeld and Feustel also replaced a key computer that processes and formats information collected by Hubble's science instruments but which shut down last September.

The astronauts will perform five spacewalks to repair the bus-sized observatory and install new instruments that will allow Hubble to send back upgraded versions of its spectacular images of distant galaxies and cosmic anomalies.

Astronomers could see the first of the images from Hubble's upgraded capacity in September.

The new camera replaces a 1990s-era digital camera with an upgraded imager that is sensitive to infrared and ultraviolet light in addition to the wavelengths the human eye can detect.

The infrared detectors are particularly important for imaging very distant objects, whose light comes to Earth shifted into longer, redder wavelengths.

Taking a long, deep look for the most distant objects detectable tops Hubble's to-do list once the observatory is back in service. The oldest targets Hubble has seen date back to 700 million years after the Big Bang, the explosion that created the universe about 13.7 billion years ago.

(Additional reporting by Irene Klotz, editing by Alan Elsner)