British astronaut Tim Peake is to assist in a spacewalk conducted by two of his fellow crewmen on the International Space Station (ISS) today.
Americans Tim Kopra - who flew to the space station with Major Peake last week - and Scott Kelly are going outside to free a jammed robotic trolley.
The Mobile Transporter, which carries a robot arm along a rail attached to the station's central support structure, became stuck on Wednesday.
During the EVA (Extra-Vehicular Activity), scheduled for 1.10pm UK time, Major Peake will be responsible for getting Kopra and Kelly in and out of their space suits and safely through the airlock.
He will also monitor the spacewalk from inside the space station and keep in touch with mission control.
The Mobile Transporter has to be repaired so that it can be latched in the right position ahead of the arrival of an unmanned Russian supply spacecraft which is due to dock in two days' time.
It will be the 191st maintenance spacewalk conducted by members of the ISS crew, the third carried out by Kelly and the second by Kopra.
Former Army Air Corps officer and helicopter test pilot Major Peake, 43, has trained to undertake EVAs and may get a chance to exercise his space legs himself during his six-month mission.
He is the first Briton aboard the space station, and the first fully British professional astronaut employed by a space agency.
Previous "Brits in space" have either had US or dual citizenship or been on privately funded or sponsored trips.
Major Peake, a father of two, was recruited and trained by the European Space Agency (Esa). The decision to send him into space came after the UK Government started to contribute funds to Esa's ISS operations in 2012.