When Space Shuttle Atlantis left Launch Pad 39A at the Kennedy Space Center on Friday, July 8, it marked the final liftoff for the long-running Space Shuttle Program, which has dominated NASA's manned operations for the past four decades. Over a 12-day mission (since extended to 13 days), the four-person crew on STS-135 will haul the Multi-Purpose Logistics Module (MPLM) Raffaello and a Lightweight Multi-Purpose Carrier (LMC) to the International Space Station. Over the course of the mission, we'll be providing daily updates.

After waking up to "More" by Matthew West at 2:59 a.m. EDT, the final Space Shuttle Atlantis crew got to work preparing for the only spacewalk scheduled for mission STS-135. In order to ready themselves for a 6.5-hour walk, Expedition 28 flight engineers Ron Garan and Mike Fossum spent an hour breathing pure oxygen through their air masks. Part of a new technique that was pioneered during STS-134, In Suit Light Exercise (ISLE) also involved dropping the air pressure in the vehicle and performing specific movements to purge nitrogen from the bloodstream. With ISLE, the astronauts are no longer required to spend a night camping out in the Quest Airlock prior to a spacewalk.

Story continues after the gallery, which will be updated as the mission wears on.

While preparations were running behind schedule, pushing the spacewalk back later than was originally anticipated, Garan and Fossum switched on the battery power to their suits at 9:22 a.m. EDT and the spacewalk was a go. Choreographed by mission specialist Rex Walheim and assisted by mission specialist Sandy Magnus and Shuttle pilot Doug Hurley, who together used the International Space Station's 58-foot-long robotic arm to push the spacewalkers around, Garan and Fossum's was a success.

The 160th spacewalk for the ISS and the 249th ever conducted by U.S. astronauts, Garan and Fossum's walk involved installing a Robotic Refueling Mission (RRM) experiment and moving a failed pump from a storage site. "Returning the module, which failed last year and disabled half of the station's cooling system, is a key objective of the STS-135 mission," NASA explained. "Engineers will diagnose what caused the failure so they can take steps to mitigate future pump module failures."

Next, Garan deployed an Optical Reflector Materials Experiment and Fossum fixed a wire that was sticking out of a portion of the Zarya module that was installed on the last Space Shuttle mission. A few more tasks were carried out by the two astronauts before the spacewalk was declared complete at 3:53 p.m. EDT after six hours and 31 minutes. All told, U.S. astronauts have spent more than 1,000 hours on spacewalks made to support and maintain the ISS.

Read more reports from the final Space Shuttle mission: Flight Day 4.