The final spacewalk to be performed by space shuttle crew astronauts is now underway, on the same day that two other spaceflight records will be set.

Space shuttle Endeavour STS-134 mission specialists Mike Fincke and Greg Chamitoff began the EVA about 35 minutes earlier than planned at 11:15 p.m. CDT on Thursday. The fourth and final STS-134 spacewalk, Fincke and Chamitoff are scheduled to be outside for about six and a half hours.


The spacewalkers' primary focus is to stow Endeavour's 50-foot robotic arm extension boom on the right-side of the station's truss structure for permanent storage. As part of that work, they will retrieve a spare robotic arm grapple fixture from the left-side of the truss and use it to replace the attachment point currently on the boom.

The astronauts will also replace fasteners on a spare arm for Dextre, the Canadian-built, multi-armed robot also referred to as the Special Purpose Dexterous Manipulator. The fasteners are left over from the spare arm's delivery to the station.

Today's spacewalk is the last by shuttle astronauts. Although STS-134 is the penultimate mission for the 30-year shuttle program, the spacewalk scheduled during the last mission, STS-135, will be conducted by space station crew members.

The first space shuttle-based spacewalk came in April 1983 during space shuttle Challenger's STS-6 mission. Astronauts Story Musgrave and Don Peterson spent 3 hours and 54 minutes during that first shuttle EVA.

In the 28 years since, space shuttle crew members have performed 162 spacewalks to rescue and repair satellites, service the Hubble Telescope and build the International Space Station.

Four hours and 47 minutes into today's EVA, Fincke and Chamitoff will log the 1,000th hour of spacewalking for the assembly and maintenance of the International Space Station. The 1,000 hours were spread over 159 shuttle- and station-based spacewalks since 1998.

Later on Friday after he is back inside the station, Fincke will set his own endurance record, surpassing chief astronaut Peggy Whitson's 376 days in space to become the U.S. astronaut with the most time on-orbit.

The shuttle and station crews began their day at 6:58 p.m. Wednesday to a parody of The Beach Boys song "Fun, Fun, Fun" with shuttle-themed lyrics, played for all six STS-134 astronauts. The same song, written by Mike Cahill for the local Houston band Mach 25, was previously played for the STS-64 crew in 2001.

One hour and 27 minutes into today's spacewalk, astronauts Mike Fincke and Greg Chamitoff completed adding space shuttle Endeavour's Orbiter Boom Sensor System (OBSS) to the International Space Station (ISS).

"On behalf of the STS-134 crew and Expedition [28] crew, space station assembly is complete," radioed Endeavour's commander Mark Kelly from inside the station, confirming installation of the boom.

The 50-foot boom, which had been used to inspect the orbiter's thermal protection system for damage, is being left on the ISS as a contingency tool for use during future spacewalks. In the event that a crew member is required to work beyond the typical reach of the station's robotic arm, the arm can take hold of the boom, increasing its length. An example might be if one of the station's outboard solar arrays needed repair, as was the case during the 2007 STS-120 mission.

As configured for the shuttle, the boom's arm attach point was located at its middle, halving its 50-foot reach when on the station's arm. To remedy this, the spacewalkers are replacing the shuttle's grapple fixture currently on one end of the boom with a station compatible grapple fixture.

Once the station power and data grapple fixture is added, the OBSS will be known as the Enhanced International Space Station Boom Assembly.

"Floating on the shoulders of giants," shuttle astronauts Mike Fincke and Greg Chamitoff completed the fourth and final spacewalk of Endeavour's STS-134 mission, the last scheduled extravehicular activity (EVA) of the 30-year space shuttle program.

During the 7 hour and 24 minute spacewalk, Fincke and Chamitoff added Endeavour's inspection boom to the station to extend its own arm's reach should it be needed in the future. The final U.S.-delivered component to be attached to the orbiting complex, the space station's assembly is now deemed to be complete.


Mike Fincke and Greg Chamitoff working on installing the boom on the station.
The spacewalkers outfitted the 50-foot boom with a new attach point for station use and then released fasteners on a spare arm for the Canadian multi-arm robot Dextre, as well as photographed experiments mounted on a payload platform installed by Endeavour earlier during the mission.

Coming back inside, Fincke and Chamitoff began repressurization of the station's Quest airlock at 6:39 a.m. CDT on Friday, marking the official end of final space shuttle crew-performed spacewalk.

A photo worth a thousand hours

Just before returning inside, Chamitoff took a few minutes to photograph the space station's sprawling modules from atop the ExPRESS Logistics Carrier-3 mounted above the complex's truss structure.


Greg Chamitoff's wide-angle photo taken from atop the station. Click to enlarge.
"At this time, now that we are almost done here, I wanted to say a few words," said Chamitoff. "This is the last flight of space shuttle Endeavour but it is also the last spacewalk by shuttle crew members for station assembly. It is kind of fitting that Endeavour is here, because Endeavour was the first shuttle to begin construction for station and so it is fitting that she's here for the last mission to finish assembly."

"During this EVA, we tallied altogether collectively over a thousand hours of spacewalks as part of station assembly. Mike and I have the honor here to share this last spacewalk and of course, with all the folks working on the ground, thousands of people who helped build this, working in the shuttle and station programs. We are floating here on the shoulders of giants."

"This space station is a pinnacle of human achievement and international cooperation. Twelve years of building and 15 countries and now it's the brightest star in the sky and hopefully the doorstep to our future."

"So congratulations everybody on assembly complete," said Chamitoff.

A spacewalk for the history books

Chamitoff and Fincke logged the 1,000th hour spacewalking in support of International Space Station assembly and maintenance at 4:02 a.m., four hours and 47 minutes into the EVA. Spread over 159 shuttle and station spacewalks performed since construction began in 1998, the total time at the end of today's EVA was 1,002 hours and 37 minutes dedicated to the space station.

It was the 118th spacewalk based out of ISS airlocks and the 248th EVA by U.S. astronauts.

Today's excursion was the second for Chamitoff, who has now logged 13 hours and 43 minutes working in outer space. It was the ninth spacewalk for Fincke, who has a total of 48 hours and 37 minutes, ranking him no. 6 on the all-time list for time spent on EVAs.

Later on Friday around 7 p.m., Fincke will set another record, surpassing chief astronaut Peggy Whitson's 376 days in space to become the U.S. astronaut with the most time on-orbit.

This spacewalk was the last by shuttle astronauts. Although STS-134 is the penultimate mission for the 30-year shuttle program, the spacewalk scheduled during the last mission, STS-135, will be conducted by space station crew members.

The first space shuttle-based spacewalk came in April 1983 during space shuttle Challenger's STS-6 mission. Astronauts Story Musgrave and Don Peterson spent 3 hours and 54 minutes during that first shuttle EVA.

In the 28 years since, space shuttle crew members have performed 164 spacewalks to rescue and repair satellites, service the Hubble Telescope and build the International Space Station.

In total, spacewalking shuttle astronauts accumulated 536 hours and 10 minutes working outside their orbiters.

Mission managers met Friday afternoon to review the data collected from the "late inspection" of the space shuttle Endeavour's thermal protection system, or heat shield, conducted on Flight Day 11.

After reviewing the imagery obtained, managers cleared the orbiter of any issues and gave a "go" for Endeavour and its crew to return to Earth.

The shuttle is scheduled to undock from the space station on Flight Day 15 just before 11 p.m. CDT Sunday. Landing is currently targeted for 1:35 a.m. Wednesday, June 1.