14 DAY TRIAL // Two members of space shuttle Endeavour's crew ventured outside the International Space Station (ISS) very early today. They will conduct the fourth and last extravehicular activity (EVA) of the STS-134 mission, and also the last spacewalk of the Space Shuttle Program (SSP).
The EVA is now being carried out by veteran astronauts Mike Fincke and Greg Chamitoff, who stepped out of the Quest Airlock aboard the station at 12:15 am EDT (0415 GMT). The spacewalk started about half an hour earlier than initially planned.
NASA says that the May 27 activity is scheduled to last about 6 and a half hours. The spacewalk is the last of any shuttle crew, since Atlantis' astronauts are not scheduled to carry out any such activity.
Atlantis will conduct its STS-135 mission with a crew of only four, and will only be tasked with delivering supplies, experiments, space parts and personal items to space. After helping their Expedition 28 colleagues unload the shuttle, they will return home to Earth.
After Fincke and Chamitoff finish their mission today, there will be no American spacewalks for several years, until private spacecraft become available to NASA. Manned vehicle capabilities are not expected to be obtained until 2015-2016.
During today's EVA, the main chore is placing the Orbital Boom Sensor System (OBSS) – the sensor-laden pole that Endeavour uses to check its heat shield while in space – on a permanent home on the outer hull of the station.
The inspection pole will be installed permanently on the space facility. STS-134 astronauts have already carried out three heat shield inspections in 10 days, and so NASA mission controllers are convinced that the orbiter can be granted a clearance for atmospheric reentry.
According to the American space agency, the third inspection took place on Thursday, May 26, with positive results. There are currently no concerns about the shuttle, as far as its heat shield goes.
During the current EVA, the two astronauts will also need to ensure the release of retention systems on the Dextre spare robotic arm, which is used to augment the capabilities of Canadarm-2, the main robotic arm on the ISS.
Today's activity also marks a momentous achievement for all the nations involved in the ISS project. Some 4 hours 46 minutes into the spacewalk, the total number of hours spent outside the station for its construction will exceed 1,000, Space reports.
At this point, Endeavour is scheduled to separate from the space lab on Sunday, May 29, and is heading for a landing on June 1. The spacecraft will return to the NASA Kennedy Space Center (KSC), in Florida.
STS-134 is Endeavour's last flight ever. After it returns home, it will be decommissioned, and then sent to the California Science Center, in Los Angeles, for permanent display.