Tim Peake explains purpose and challenges of spacewalk
British astronaut Tim Peake has been explaining the purpose of the spacewalk which he will carry out with fellow astronaut Tim Kopra on Friday 15 January.
Major Tim told BBC Stargazing Live that they would replace a failed power unit called a Sequential Shunt Unit - which would be challenging even in weightlessness due to its large mass and momentum.
He will also be laying new electrical cable, which he described as, "fraught with peril".