CAPE CANAVERAL, Fla. » Two astronauts stepped into the history books on the fourth and final spacewalk of NASA’s next-to-last shuttle mission Friday, installing an extension pole at the International Space Station and officially ending its construction.

"Space station assembly is complete," space shuttle Endeavour’s commander, Mark Kelly, announced once the boom was securely latched.

Spacewalkers Mike Fincke and Gregory Chamitoff teamed up with robot arm operator Gregory Johnson to attach the 50-foot boom to the orbiting lab.

Fincke and Chamitoff are the last shuttle crew members to perform a spacewalk. All future spacewalks — including one during the final shuttle voyage this summer — will be performed by full-time space station residents.

Another milestone was within close reach: 1,000 hours of spacewalking at the orbiting outpost.

Before Friday morning, astronauts had logged 995 hours outside for space station assembly and maintenance. With a planned excursion of 6 1/2 hours — the 159th spacewalk to build the station and keep it humming since 1998 — Fincke and Chamitoff were poised to hit the 1,000-hour mark before going back inside.

The space station’s new boom was used by shuttle Endeavour’s crew on Thursday to survey their ship one last time in orbit. They attached the camera- and laser-tipped pole to a robot arm to check for micrometeorite damage.

NASA expects to finish reviewing the 3-D images Friday; if everything looks good, managers will clear Endeavour for next week’s trip home.

The boom, which launched aboard Endeavour, will remain permanently at the space station and assist with future repairs, especially in hard-to-reach areas.

Endeavour, now docked at the space station, is making its last flight before being retired to a museum in California. Atlantis will close out the 30-year shuttle program in July.

"Beautiful Endeavour," Fincke called out as the spacewalk got under way. "She’s a great ship."

"Looks like she belongs right there," Chamitoff agreed.

The spacewalkers also savored the views 220 miles below.

"Most beautiful planet in the solar system — wow," Fincke said.

Later Friday, Fincke will surpass the U.S. record of 377 days in space. He spent six months living on the space station — twice. This is his first shuttle trip; he previously rode Russian Soyuz rockets into orbit.

"I could not share this moment with a group of better people, including our friends on the ground," Fincke radioed.

Endeavour and its crew of six will leave the space station late Sunday night. Landing is set for the predawn hours of Wednesday during a rare touchdown in darkness.