MIAMI (AFP) - French astronaut Thomas Pesquet floated into space on his first-ever spacewalk Friday (Jan 13), 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 (7:22pm Singapore time), 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 finish power maintenance work.

This includes connecting several modern lithium-ion batteries - which weigh about 194kg each - to store power for the orbiting lab as it flies in Earth shadow.

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

In all, 12 old nickle hydrogen batteries - of a total of 48 on board the ISS - are being replaced with the newer lithium-ion types as part of this month's spacewalks. Eventually, all will be replaced and upgraded.

Pesquet, 38, is the fourth French astronaut to perform a spacewalk.

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