Much like any other scientific instrument on Earth, the International Space Station is also prone to occasional breakdowns. What makes the orbital facility different though is that it takes a special kind of "mechanic" to fix it.

The ISS recently experienced problems with one of its power units, and it's up to Tim Peake of the European Space Agency and Tim Kopra of NASA to make the necessary repairs.

The astronaut duo is set to carry out a spacewalk outside the ISS on Friday, Jan. 15, marking the 35th extravehicular activity (EVA) that NASA has facilitated.

Those who want to see Tim Peake and Tim Kopra's spacewalk live can watch it via NASA's channels starting 6:30 a.m. EST today. [Editor's Note: We have embedded the video stream below.]

It is also a milestone for the ESA as Peake is poised to become the first British ESA astronaut in history to participate in a spacewalk.

Peake and Kopra are to be assisted by Russian cosmonaut Sergey Volkov, who will monitor the astronauts' progress from within the ISS. The repairs are expected to be completed within 6 hours.

Preparing For The Spacewalk

As part of their scheduled EVA, Peake and Kopra are already preparing their tools and suits for the mission. Compared to carrying out repairs on Earth, a spacewalk requires a well thought out plan and involves choreographed movements to reduce the likelihood of accidents.

Equipment and tools are organized in detail and attached to the suits of the astronauts before going on to the mission outside the orbital facility.

Prior to their spacewalk, Peake and Kopra will take part in "prebreathing" exercises for up to 2 hours in order to prepare their bodies for the low pressure inside their extravehicular mobility units (EMU).

Without prebreathing, an astronaut participating in a spacewalk could suffer from decompression sickness, or more commonly known as the bends. This condition occurs when the nitrogen in the body turns into bubbles because of sudden shifts in pressure.

Astronauts have to breathe in pure oxygen to prevent their bodies from taking in nitrogen and to avoid experiencing the bends.

Once they finish their preparations, the two astronauts will then step into the Quest airlock, where the pressure around them will be lowered. Their spacewalk officially begins when they open the outside hatch of the ISS.

Repairing The Power Unit And Laying Cables

After carrying out a "buddy-check" to see if their equipment and tools are in order, Peake and Kopra will then proceed to their designated points along the exterior of the ISS. Each point has a Sequential Shunt Unit (SSU), which the duo will have to inspect.

Once they reach the failed SSU, Peake will hand Kopra the replacement unit to have it installed. Members of NASA's ground control will then conduct checks on the SSU. The astronauts will make their way back to the airlock to secure the failed SSU.

The second part of their spacewalk involves having the duo conduct maintenance work on other aspects of the ISS such as replacing the Non Propulsive Valve that was removed in an earlier spacewalk by fellow astronauts and fixing cables from the station's Destiny Laboratory.

If Peake and Kopra are able to finish their work ahead of time, officials from ground control may also give them extra work to maximize the remaining time during the spacewalk.

Returning To The ISS

The EVA is expected to wrap up in 6 hours and 20 minutes, during which the two astronauts will not be able to eat or even take a toilet break. They can drink water from a pouch using a straw.

The spacewalk will also test Peake and Kopra's patience and stamina as they fight against their pressurized suits, which tend to become stiff while in the vacuum of space.

Following their work outside the ISS, the duo will then return to the airlock where they will clean up for about 25 minutes. The airlock will then repressurize, allowing Peake and Kopra to return to the safety of the space station.

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