Shuttle astronauts mark milestones outside space station

Spacewalker Mike Fincke photographed the Cupola today. (NASA)

Shuttle Endeavour astronauts ventured outside the International Space Station one final time to perform several robotic chores as they marked a few milestones outside the outpost.

The fourth and final spacewalk by Endeavour's astronauts began earlier than planned at 12:15 a.m. EDT this morning, from the space station's Quest airlock.

Astronauts Mike Fincke and Greg Chamitoff went to work on the first task which will double the length and extend the reach of the space station's robotic arm.

Endeavour's orbiter sensor boom extension which was used to survey the orbiter's thermal protection system earlier on this flight for damage, was handed over to the space station to become a permanent fixture.

The orbital duo moved the boom over to the station's side for future use to double the reach of the existing arm to over 100-feet long.

It was also the final American equipment to be installed on the orbiting laboratory 220 miles high.

"Space station assembly is complete," Endeavour's commander Mark Kelly radioed his crew with pride.

"Assembly complete, amazing. Boy, this is a big space station," Chamitoff radioed back moments later from outside the complex.

Chamitoff also became the final shuttle astronaut to return inside an airlock as he followed Fincke to closeout this 159th spacewalk to construct and maintain the nearly one million pound complex.

The astronauts wrapped up their 7 hour and 24 minute spacewalk today at 7:39 a.m., completing 28 hours and 44 minutes of spacewalks performed during Endeavour's final flight.

The astronauts surpassed the 1000th hour of spacewalking time at 5:02 a.m. in support of constructing and maintaining the space station.

Since 1998, American, Russian, Canadian, European and Japanese astronauts have now spent 1,002 hours and 37 minutes of spacewalking time outside the station.

Today's spacewalk was also the final spacewalk performed by a space shuttle crew.

All future spacewalks will be performed by space station astronauts, including the single orbital walk planned during shuttle Atlantis' flight in July.

Also later today at 8:00 p.m., Fincke will become the American astronaut with the most time spent in space as he surpasses his boss Peggy Whitson's 377 days in space.

Whitson serves as the Chief of the Astronaut Corps at the Johnson Space Center.

Fincke served two six month tours aboard the station in 2004 and 2009, the later as the commander.

His two previous space flights ended with landings in Kazakhstan aboard Russian Soyuz spacecrafts. This flight aboard Endeavour is his first space shuttle flight.