Suni Williams, the station's commander, had to tackle some overdue outdoor repair work alongside NASA's Nick Hague.
They emerged as the orbiting lab sailed 420km above Turkmenistan.
"I'm coming out," Williams radioed.
Plans called for Williams to float back out next week with Butch Wilmore.
LIVE: Two — NASA (@NASA) @NASA_Astronauts, Nick Hague and Suni Williams, step outside of the @Space_Station to support station upgrades, including repairs to our NICER (Neutron star Interior Composition Explorer) X-ray telescope. https://t.co/0VP296OmRYJanuary 16, 2025
Williams and Wilmore launched aboard Boeing's new Starliner capsule last June on what should have been a week-long test flight.
But Starliner trouble dragged out their return, and NASA ordered the capsule to come back empty.
Then SpaceX delayed the launch of their replacements, meaning the two will not be home until late March or early April - ten months after launching.
It was the first spacewalk by NASA astronauts since an aborted one in June.
US spacewalks were put on hold after water leaked into the airlock from the cooling loop for an astronaut's suit.
NASA said the problem has been fixed.
This was the eighth spacewalk for Williams, who has lived on the space station before.
15°C