At 12:45 GMT, NASA astronauts began the last spacewalk of 2015 leaving Britain's Tim Peake in charge of the US section of the International Space Station.
Both Tim Kopra and Scott Kelly are venturing outside the spacecraft to fix a jammed rail car, which is expected to take around three hours.
Peake will be monitoring both his colleagues while they make the repairs.
Tweeting ahead of the move, he said: "Busy day on #ISS today preparing possible EVA for @astro_tim & @StationCDRKelly tomorrow. My job is to help them get out and back safely."
On Tuesday, Peake made British history, becoming the first UK astronaut to launch into space.
- Tim Peake: Who Is He? When Is The Launch? What Is His Mission Aboard The International Space Station?
- Tim Peake: How Life Will Change For The British Astronaut Once Aboard The ISS
- Timothy Peake: Five Ways The UK Astronaut's Body Will Change While Aboard The International Space Station
- Timothy Peake Sends Last Tweet Before Liftoff To International Space Station
- Revealed: The UK's First Astronaut's Mission Patch
- British Astronaut Major Timothy Peake Confirmed For Space Station Mission
- International Space Station: 15 Years In 50 Pictures
On arrival, the first person he spoke to back home was his mother, Angela. She told him: "Hello Tim. I think you would call today a spectacular day in the office."