During the spacewalk, which lasted 7 hours and 16 minutes, U.S. astronauts Steve Swanson and Patrick Forrester attempted to retract a P6 solar array and prepare a Solar Alpha Rotary Joint (SARJ), which will allow the arrays to rotate toward the sun.
But the astronauts were unable to complete the mission, and will continue their work during a third spacewalk planned for Friday at 8.38 p.m. Moscow time (4.38 p.m. GMT).
Jim Reilly coordinated the spacewalk on the orbital station with Lee Archambault controlling the robotic arm.
NASA chiefs decided to extend the space shuttle's mission by two days Monday, after an inspection of the shuttle's exterior revealed slight damage to its thermal blanket. Repairs will be carried out during the third spacewalk.
In 2003 similar heat shield damage led to the disintegration of a Columbia shuttle, which resulted in the death of seven astronauts on re-entry into Earth's atmosphere.
Shuttle Atlantis will now return to Earth on June 21.
