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| Tim Peake set for historic spacewalk | Tim Peake set for historic spacewalk |
| (about 11 hours later) | |
| Tim Peake is set to carry out the first ever spacewalk by an "official" British astronaut. | Tim Peake is set to carry out the first ever spacewalk by an "official" British astronaut. |
| Major Peake and Nasa astronaut Tim Kopra are scheduled to step outside the International Space Station at 12:55 GMT. | Major Peake and Nasa astronaut Tim Kopra are scheduled to step outside the International Space Station at 12:55 GMT. |
| They will replace a faulty component on the station's exterior, which has compromised a power channel on the outpost. | They will replace a faulty component on the station's exterior, which has compromised a power channel on the outpost. |
| Michael Foale became the first Briton to carry out a spacewalk in 1995. | Michael Foale became the first Briton to carry out a spacewalk in 1995. |
| He flew under a US banner with Nasa. | He flew under a US banner with Nasa. |
| "I think a spacewalk is absolutely the pinnacle of an astronaut's career," Major Peake told BBC Stargazing Live this week. | "I think a spacewalk is absolutely the pinnacle of an astronaut's career," Major Peake told BBC Stargazing Live this week. |
| The European Space Agency (Esa) astronaut added: "We've put a huge amount of effort into this spacewalk. It's hugely exciting and we're ready to go." | The European Space Agency (Esa) astronaut added: "We've put a huge amount of effort into this spacewalk. It's hugely exciting and we're ready to go." |
| The six-and-a-half hour extra-vehicular activity (EVA) - the technical term for a spacewalk - will see the two Tims replace a failed electrical box which regulates power from the solar panels. | The six-and-a-half hour extra-vehicular activity (EVA) - the technical term for a spacewalk - will see the two Tims replace a failed electrical box which regulates power from the solar panels. |
| Note: This tracker uses the time set on the device you are using to predict where the space station is. If your pc, tablet or mobile has the wrong time set then the graphic will not show the correct position. | Note: This tracker uses the time set on the device you are using to predict where the space station is. If your pc, tablet or mobile has the wrong time set then the graphic will not show the correct position. |
| They will venture to the very edge of the space station, travelling half its length - a distance of roughly 50m, which is equivalent to an Olympic-sized swimming pool. | |
| Before the spacewalk, the astronauts spend two hours breathing pure oxygen to purge their bodies of nitrogen. This helps them avoid decompression sickness - also known as "the bends" - which is caused by quick changes in pressure and can cause serious symptoms. | |
| Peake and Kopra will move along the exterior using their arms, but will be attached to the space station's external structure via a steel cord, or tether. Once they get to the worksite, they will attach another tether as an additional measure to prevent them drifting into open space. | Peake and Kopra will move along the exterior using their arms, but will be attached to the space station's external structure via a steel cord, or tether. Once they get to the worksite, they will attach another tether as an additional measure to prevent them drifting into open space. |
| Colonel Kopra will head out of the Quest airlock first; laying down anchor points on the outside of the ISS. The US astronaut will then give a "Go" signal and Major Peake will follow his colleague, carrying the replacement box. | Colonel Kopra will head out of the Quest airlock first; laying down anchor points on the outside of the ISS. The US astronaut will then give a "Go" signal and Major Peake will follow his colleague, carrying the replacement box. |
| "I'll have a few moments where I'll just be hanging beneath the airlock and I can have a look around... look down on planet Earth and see what that feels like," said Major Peake. | "I'll have a few moments where I'll just be hanging beneath the airlock and I can have a look around... look down on planet Earth and see what that feels like," said Major Peake. |
| Luca Parmitano, an Italian Esa astronaut who conducted two spacewalks in 2013, told BBC Five Live: "It is unimaginable... there are no words to describe the feeling of seeing our planet from above through a visor - that's all that separates us from the view, a thin visor of plexiglass." | |
| "When language evolved, it described what we saw around us. Being on the space station, doing an EVA, walking outside is not something we have experienced [as a species]." | "When language evolved, it described what we saw around us. Being on the space station, doing an EVA, walking outside is not something we have experienced [as a species]." |
| Both astronauts have trained in a large indoor water tank called the Neutral Buoyancy Laboratory at Houston's Johnson Space Center. | Both astronauts have trained in a large indoor water tank called the Neutral Buoyancy Laboratory at Houston's Johnson Space Center. |
| Nasa astronaut Michael López-Alegría, who holds the US record for cumulative spacewalking time, said the two Tims were well prepared, but added that there were key differences between underwater training and a real EVA. | Nasa astronaut Michael López-Alegría, who holds the US record for cumulative spacewalking time, said the two Tims were well prepared, but added that there were key differences between underwater training and a real EVA. |
| "One is that translation [moving from one point to another] in quite a bit different without the viscosity of the water," he told BBC News. | "One is that translation [moving from one point to another] in quite a bit different without the viscosity of the water," he told BBC News. |
| "This is especially true when [Major Peake] will be transporting relatively large masses (like the SSU) relatively long distances. This fact will change his centre of gravity and will affect the results of the inputs he makes with his hands and arms during translation." | "This is especially true when [Major Peake] will be transporting relatively large masses (like the SSU) relatively long distances. This fact will change his centre of gravity and will affect the results of the inputs he makes with his hands and arms during translation." |
| But he explained: "This kind of thing is 'all in a day's work' for a spacewalker. I'm very confident that the two Tims will complete their tasks with great skill, efficiently and, most importantly, safely." | But he explained: "This kind of thing is 'all in a day's work' for a spacewalker. I'm very confident that the two Tims will complete their tasks with great skill, efficiently and, most importantly, safely." |
| The failed electrical component - known as a Sequential Shunt Unit (SSU) - is relatively straightforward to swap out: it involves undoing just one bolt. | The failed electrical component - known as a Sequential Shunt Unit (SSU) - is relatively straightforward to swap out: it involves undoing just one bolt. |
| But the ISS takes 90 minutes to orbit the Earth, so the astronauts experience 45 minutes of daylight followed by 45 minutes of total darkness. | But the ISS takes 90 minutes to orbit the Earth, so the astronauts experience 45 minutes of daylight followed by 45 minutes of total darkness. |
| Peake and Kopra can only work on the SSU in darkness, because in daylight, there could be a current running through the box. | Peake and Kopra can only work on the SSU in darkness, because in daylight, there could be a current running through the box. |
| Tim Peake in space: Want to know more? | Tim Peake in space: Want to know more? |
| Special report page: For the latest news, analysis and video | Special report page: For the latest news, analysis and video |
| Guide: A day in the life of an astronaut | Guide: A day in the life of an astronaut |
| Explainer: The journey into space and back | Explainer: The journey into space and back |
| Test yourself: Do you have what it takes to be an astronaut? | |
| Social media: Twitter looks ahead to lift-off | Social media: Twitter looks ahead to lift-off |
| Timeline: How Tim Peake became a British astronaut | |
| Quiz: How dangerous is life in space? | |
| They have been given a safe window of 31 minutes to work on changing the SSU. | They have been given a safe window of 31 minutes to work on changing the SSU. |
| "We have to be very careful when we go out to the worksite, because there's nothing protecting us from the high voltages generated by the solar panel," said Major Peake. | "We have to be very careful when we go out to the worksite, because there's nothing protecting us from the high voltages generated by the solar panel," said Major Peake. |
| "We need to change that box out and then hopefully the fresh one will work correctly and we can continue with some more tasks." | "We need to change that box out and then hopefully the fresh one will work correctly and we can continue with some more tasks." |
| After changing the SSU, Major Peake will carry the failed box back to the starting point. | After changing the SSU, Major Peake will carry the failed box back to the starting point. |
| The astronauts will also deploy cables for new docking ports and reinstall a valve that was removed for relocation of the station's Leonardo module last year. | The astronauts will also deploy cables for new docking ports and reinstall a valve that was removed for relocation of the station's Leonardo module last year. |
| Michael Foale, who was born in Louth, Lincolnshire, became the first Briton to make a spacewalk on 9 February 1995, during a US space shuttle mission. | Michael Foale, who was born in Louth, Lincolnshire, became the first Briton to make a spacewalk on 9 February 1995, during a US space shuttle mission. |
| Born to a British father and American mother, Mr Foale has dual British and US citizenship. He was selected under Nasa's astronaut programme and therefore "flew" as an American. | Born to a British father and American mother, Mr Foale has dual British and US citizenship. He was selected under Nasa's astronaut programme and therefore "flew" as an American. |
| Traditionally, the British government has not funded human spaceflight, leading a generation of budding astronauts to look to the US space agency as their only route to orbit. | Traditionally, the British government has not funded human spaceflight, leading a generation of budding astronauts to look to the US space agency as their only route to orbit. |
| But the UK changed its policy after Mr Peake was selected in 2009 as a European Space Agency astronaut. Thus, Mr Peake is the first person since Helen Sharman in 1991 to wear the British flag in space. | But the UK changed its policy after Mr Peake was selected in 2009 as a European Space Agency astronaut. Thus, Mr Peake is the first person since Helen Sharman in 1991 to wear the British flag in space. |
| Follow Paul on Twitter. | Follow Paul on Twitter. |