French astronaut Thomas Pesquet floated into space on his first-ever spacewalk Friday, on a mission to help upgrade the power system outside the International Space Station with new, refrigerator-sized lithium-ion batteries.

Wearing a white spacesuit with the French flag emblazoned on one shoulder, Pesquet and American astronaut Shane Kimbrough switched on their spacesuits' internal battery power to mark the official start of the spacewalk at 6:22 am (1122 GMT), more than a half hour earlier than scheduled.

"This is Pesquet's first foray into the vacuum of space," a NASA commentator said as a live broadcast from the US space agency showed Pesquet's booted feet dangling out of the airlock as he made his way outside.

The men's goal for the six-and-a-half hour spacewalk is to connect adapter plates for three modern lithium-ion batteries.

The new batteries weigh about 428 pounds (194 kilograms) each, and replace older, but far lighter, nickel hydrogen batteries.

The batteries' role is to store power for the orbiting lab as it flies in Earth shadow.

The space station travels at a speed of more than 17,000 miles (27,350 kilometers) per hour, and circles the Earth about every 90 minutes, periodically moving through light and darkness.

The power upgrade work was begun earlier this month during a spacewalk by Kimbrough and American astronaut Peggy Whitson.

Eventually, all 48 of the old batteries on board will be replaced with new ones.

- First outing for Pesquet -

Pesquet, 38, is the fourth French astronaut to perform a spacewalk, and the 11th European.

He posted pictures of the space station on Facebook Thursday, showing the location of the batteries and the Quest airlock, which is the entry and exit portal for spacewalkers.

"We will get a closer look of the outside of the space station," he wrote.

"Peggy says it is even more beautiful when you are out there than looking through the windows."

The spacewalk was the 197th for maintenance and assembly at the orbiting outpost, a global science collaboration of more than a dozen nations including Russia, the United States and Japan.

- Friend at mission control -

Back at mission control in Houston, Texas, Italian astronaut Luca Parmitano orchestrated the spacewalk and could be heard giving the men directions.

The European Space Agency described Parmitano's role as lead communicator as "a recognition of ESA's expertise in station operations."

Parmitano went on two spacewalks during his six-month mission in 2013.

Shortly after the start of one of those spacewalks, Parmitano's helmet began filling with a water leak and he had to be rushed back inside the station for emergency aid.

Parmitano is also a friend of Pesquet's. They trained together for six years in the European astronaut corps.

Parmitano said that ahead of Friday's spacewalk, he gave Pesquet some words of advice: go slow and take plenty of pictures.

About an hour into Friday's outing, Parmitano asked the astronauts to check and inspect their helmets and gloves. Both reported they were dry and in good shape.