June 26 (UPI) -- Two NASA astronauts conducted a spacewalk to replace lithium ion batteries outside of the International Space Station on Friday with only a minor snafu -- the loss of a mirror.
Astronauts Chris Cassidy and Robert Behnken began the spacewalk at 7:32 a.m. EDT and were back safely inside the ISS just over 6 hours later.
Upon first exiting the ISS, though, Cassidy said a small mirror became detached from his spacesuit and floated into space. Astronauts use small mirrors on their spacesuits to help them see different angles while on spacewalks.
NASA said the loss of the mirror didn't pose a hazard and allowed the spacewalk to continue.
The spacewalk was the seventh for Cassidy, while Behnken ventured in open space for the eighth time.
Friday's spacewalk was the first of four to replace old nickel-hydrogen batteries with new lithium-ion batteries. The next spacewalk is scheduled for Wednesday.
Behnken and fellow NASA astronaut Douglas Hurley lifted off from NASA's Kennedy Space Center in Florida on May 30 in a commercially built and operated spacecraft, the SpaceX Crew Dragon. It marked the first time in history NASA astronauts left American soil in a commercial spacecraft.
It also ended a nine-year absence of human spaceflight from U.S. territory and was the first time since the final space shuttle mission in 2011 that NASA astronauts didn't have to rely on Russia to get into space.
Behnken and Hurley docked with the Space Station May 31. Cassidy and Russian cosmonauts Anatoly Ivanishin and Ivan Vagner were already aboard the station.