Astronaut Andrew Feustel, mission specialist, performs work on the Hubble Space Telescope in this photo provided Thursday by NASA as the first of five STS-125 spacewalks kicks off a week’s work on the orbiting observatory. The shuttle is perched on the end of the Canadian-built remote manipulator system. Feustel, teamed with astronaut John Grunsfeld, not pictured, will join the veteran spacewalker on two of the remaining four sessions of extravehicular activity later in the mission.

Cape Canaveral, Fla. ? A pair of spacewalking astronauts overpowered a stubborn bolt and successfully installed a new piano-sized camera in the Hubble Space Telescope on Thursday, the first step to making the observatory better than ever.

“Let there be light,” spacewalker John Grunsfeld said as ground controllers checked the power hookups.

Grunsfeld and Andrew Feustel also completed other major chores, replacing a science data-handling unit that broke last fall and hooking up a docking ring so a robotic craft can guide Hubble into the Pacific years from now.

The nearly 7 1/2-hour repair job — all the more dangerous because of the high, debris-ridden orbit — got off to a slow and rocky start.

John Grunsfeld and Andrew Feustel had trouble removing the old camera from the telescope because a bolt was stuck. They fetched extra tools, but none seemed to work.

Finally, Mission Control urged the astronauts to use as much force as possible, even though there was a risk the bolt might break. If that had happened, the old camera would have been stuck inside, leaving no room for its souped-up replacement.

“OK, here we go,” Feustel said. “I think I’ve got it. It turned. It definitely turned.” And then: “Woo-hoo, it’s moving out!”

The extra effort paid off but put the astronauts a little behind schedule in their first spacewalk of shuttle Atlantis’ mission. In all, five high-risk spacewalks are planned to fix Hubble’s broken parts and plug in higher-tech science instruments.

Atlantis and its crew are traveling in an especially high orbit, 350 miles above Earth, that is littered with pieces of smashed satellites. A 4-inch piece of space junk passed within a couple miles of the shuttle Wednesday night, just hours after the shuttle grabbed Hubble. Even something that small could cause big damage.

For the first time, another shuttle is on standby in case it needs to rush to the rescue.

Once the bolt was freed, Feustel pulled out the old camera, the size of a baby grand piano.

“This has been in there for 16 years, Drew,” said Grunsfeld, “and it didn’t want to come out.”

The spacewalkers followed up with the installation of the new camera. From inside Atlantis, spacewalk overseer Michael Massimino congratulated Grunsfeld and Feustel for “adjusting to the curve ball that was thrown at you.”

The initial bolt problems caused some anxiety for Hubble officials on the ground.

“I’m five years older now than when I came to work this morning,” Hubble senior scientist David Leckrone said during an afternoon news conference. “I just hope the rest of the mission is a little bit smoother.”

The newly inserted wide-field and planetary camera — worth $132 million — will allow astronomers to peer deeper into the universe, to within 500 million to 600 million years of creation.

The old one was installed in December 1993 during the first Hubble repair mission, to remedy the telescope’s blurred vision.

It had corrective lenses already in place and, because of the astounding images it captured, quickly became known as the camera that saved Hubble. It’s also been dubbed the people’s telescope because its cosmic pictures seem to turn up everywhere.

The camera — which has taken more than 135,000 observations — is destined for the Smithsonian Institution.