Astronaut Randy Bresnik along with Mark Vande Hei replaced the latching end of the 57-foot-long Canadian-made robot arm, called Canadarm2.
The task involved usage of using a grease gun, which resembles a caulking gun, to keep the latching mechanism working smoothly. These latches or hands are located on each of robot arm and are used to capture incoming cargo ships that ferry supplies to the crew living in orbit.
"The spacewalk formally began when the duo switched their spacesuits to battery power at 1156 GMT, then floated out into the vacuum of space", NASA said. It ended six hours and 26 minutes later.
The job is expected to spill into next week, in a third spacewalk. Bresnik will also lead the next spacewalk October 18.
Launched 16 years ago, these latches have become obsolete and NASA plans to replace the latching mechanism on the opposite end of the arm early next year.