Tim Peake is to become Britain’s first ever person to walk in space when he jumps out of the International Space Station.
Major Peake will set out alongside Nasa’s Tim Kopra to repair a broken power unit on the space station.
The two will be outside of the space station on what is referred to as an “Extra-Vehicular Activity (EVA)” for six-and-a-half hours, during which there will be no toilet breaks. The walk will begin at 12.55.
During that time there will be two blocks of daylight for 45 minutes, as the station catches the sun on its journey round the Earth. The rest of the mission will be done in complete darkness.
The two have been preparing for the walk since not long after Major Peake arrived on board the station, last month. But there was also months of practising for such an event while on Earth.
The two astronauts will undertake what the European Space Agency (ESA) has described as a minutely choreographed work to fix a broken power unit. The unit doesn’t cause a problem at the moment because the space station has more solar panels than it needs, but it wil get it back up to full functioning.
Major Peake will begin to breathe pure oxygen two hours prior, because the pressure inside their suits is lower than that of the ISS.
The pair will enter an airlock before opening its hatch and heading outside.
Like rock climbers, the astronauts must always be tethered to Space Station supports.
Colonel Kopra will lead, heading to the solar units that need to be repaired. Once given the green light, Major Peake will follow with the replacement equipment.
They should finish the repairs in under three hours, and at that point ground control will perform some checks.
During the second half of the EVA, the astronauts will lay cables for new docking ports and reinstall a valve that was removed last year.
If they are ahead of schedule, the pair will be assigned "bonus tasks", including laying another cable and cutting some unnecessary power caps.
The ESA warned: "A spacewalk is a test of patience and alertness."
The six hours will be tiring for the pair as they fight against the pressurised suits. Sunrises can also be "blinding for moments" from space, according to the ESA, and they will need to check on each other frequently and make sure their suits have no damage.
They will be able to drink water from pouches, but will not have a toilet break.
Once they return, their colleagues inside the station will help with a 25-minute clean-up and further checks. Only then will they be able to get out of their suits and adjust to the pressure back in the station.
There have been 191 spacewalks for maintenance at the space station, including a similar walk completed in 2014 by Nasa astronaut Reid Wiseman, who will help guide the current EVA from mission control in Houston.
Major Peake, a former Army Air Corps and helicopter test pilot, is the first Briton aboard the ISS 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.
He arrived at the ISS on December 15 and will stay for six months.
Additional reporting by Press Association
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