What is a spacewalk, and what is British astronaut Tim Peake doing on his?

Tim Peake will be carrying out the first spacewalk by a Brit since 1995, but what exactly will he be doing?

British astronaut Tim Peake is set to carry out a spacewalk today at 12:55 GMT. It will be the first time a British astronaut has officially carried out this exhilarating task under the European Space Agency’s name. Former British astronaut Michael Foale was the first Brit to carry out a spacewalk, on NASA’s watch.

But what exactly is a spacewalk?

Technically, a spacewalk is any activity done by an astronaut in space outside of a spacecraft and away from earth’s atmosphere, but usually refers to maintenance and repair work on the International Space Station (ISS).

Tim Peake will be joined by NASA’s Tim Kropa in replacing an external power regulator (also known as the sequential shunt unit), installing a valve and attaching cables to the outside of the ISS. The task carries high risks, as they will have only 30 minutes to swap out the power regulator while the ISS is in the Earth’s shadow to avoid high-voltage sparks.

The ISS orbits the Earth in a 90-minute cycle – meaning the astronauts experience cycles of 45 minutes of darkness and 45 minutes of light. The entire spacewalk itself will last six and a half hours, each stage thoroughly planned in a timeline that spans almost 40 pages, according to Peake’s blog.

Both astronauts have practised at NASA’s Johnson Space Centre in Houston, Texas, and also in space, and are looking forward to the task. “I think a spacewalk is absolutely the pinnacle of an astronaut’s career,” Peake told BBC’s Stargazing Live earlier in the week.

Nonetheless, it won’t be easy. Former NASA astronaut Dr Nicholas Patrick told Radio 4’s Today programme, “It is one of the hardest things astronauts ever have to do”. Spacewalks, or extravehicular activity (EVA), take years of training beforehand. This includes experiencing the sensation of floating in swimming pools, preparing for worst-case scenarios using virtual reality headsets, and simply wearing the space suit, which is heavy and includes a fixed helmet that doesn’t move.

Patrick’s STS-116 Discovery mission in 2006 involved multiple EVAs, such as rewiring the power system of the ISS, changing the solar panels and swapping out two tonnes of unneeded items for two tonnes of equipment and supplies.

Patrick went on to say it is a physical challenge – needing to train your hands and forearms to have enough energy to carry out such tasks – but also a mental one. This includes planning where to set tools after they’ve been used in order to avoid obstruction and focus solely on the essential EVA work.

However, he did say it was important to try to enjoy the view and recognise the significance of floating in space: “It’s the astronaut’s equivalent of stopping to smell the roses”.

NASA is livestreaming the event, which you can watch below.