Endeavour astronauts Mike Fincke, left, and Greg Chamitoff, completed construction of the International Space Station Friday with the smooth addition of an extension boom. (NASA/Associated Press)

Two astronauts made history Friday as the final spacewalkers of NASA's 30-year shuttle program, completing construction of the International Space Station with the smooth addition of an extension boom.

"This space station is the pinnacle of human achievement and international cooperation," spacewalker Gregory Chamitoff observed before heading back inside.

"Twelve years of building and 15 countries and now it's the Parthenon in the sky and hopefully the doorstep to our future. So congratulations everybody on assembly complete."

Chamitoff said it was fitting for Endeavour to be present at the end of space station construction since it was present for the first assembly mission in December 1998. It was the fourth spacewalk in a week for the Endeavour astronauts, headed back to Earth in just a few days to end NASA's next-to-last shuttle flight.

Chamitoff and his spacewalking partner, Mike Fincke, teamed up with robot arm operator Gregory Johnson to accomplish this last construction job.

"Assembly complete. Amazing," Chamitoff said once the 50-foot boom was latched securely in place. "Boy, this is a big space station," he marvelled several minutes later.

All future spacewalks — including one during the final shuttle voyage this summer — will be performed by full-time space station residents. The Endeavour astronauts wished the future spacewalkers well as the hatch to the outside was shut.

1st spacewalk in 1983

This was the 164th spacewalk by shuttle astronauts; the first was performed back in 1983. The bulk — 110 — were for the International Space Station, and 23 involved the Hubble Space Telescope.

Another milestone was achieved Friday: 1,000 hours of spacewalking at the orbiting outpost.

Before Friday morning, astronauts had logged 995 hours outside for space station assembly and maintenance. Fincke and Chamitoff hit the 1,000-hour mark five hours into their 7½-hour spacewalk, the 159th by all countries to build the station and keep it humming.

The space station's newly attached boom was used by shuttle Endeavour's astronauts Thursday to survey their ship for micrometeorite damage. NASA expects to finish reviewing the 3D images Friday. If everything looks good, managers will clear Endeavour for next week's trip home.

The boom will remain permanently at the space station and assist with future repairs, especially in hard-to-reach areas. Fincke and Chamitoff put an attachment on one end of the pole for the space station's 18-metre robot arm — which would stretch 33 metres when grasping the boom — and disconnected the no-longer-needed laser sensors at its tip.

Besides the boom, Endeavour delivered a $2 billion particle physics detector that was placed on the station last week.

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

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 pre-dawn hours of Wednesday during a rare touchdown in darkness.

While NASA's role in space station construction is over, the Russian Space Agency may add another chamber or two in years to come. The Russians also will continue to provide rides to and from the orbiting lab for U.S. astronauts until private companies in America are able to take over the job.