Watch Astronauts Fix the International Space Station in NASA Livestream

NASA is hosting a livestream showing a spacewalk by two astronauts as they help maintain crucial cooling systems aboard the International Space Station (ISS).

The spacewalk livestream began at 7:30 a.m. ET on Wednesday morning as NASA astronaut Raja Chari and European Space Agency (ESA) astronaut Matthias Maurer were preparing to exit the ISS and step into the vast vacuum of space.

The astronauts, wearing their spacesuits, then entered the ISS airlock where the atmospheric pressure was slowly decreased so that they could safely exit the station.

The spacewalk began at around 8:30 a.m. ET and will run for around six-and-a-half hours. It can be viewed on NASA's Twitter feed here, as well as on the NASA Live section of NASA's website.

During the spacewalk, Chari and Maurer will install hoses on a radiator component of the ISS. Together, these hoses and the radiator system direct ammonia through the space station's cooling systems, removing excess heat and keeping the station at an ideal temperature.

The two astronauts will also be carrying out other upgrades to the station's hardware, including installing a power and data cable and replacing an external camera.

The spacewalk will be the first for Maurer, who arrived at the ISS on November 11 last year aboard a SpaceX Dragon capsule, along with crewmates Thomas Marshburn, Kayla Barron, and current spacewalk colleague Raja Chari.

Maurer was born in Sankt Wendel, Germany. A doctor of materials science, he participated in the selection process for ESA astronauts in 2008 and 2009 and formally joined the European astronaut corps in 2015.

For Chari, this spacewalk is the second of his career. Born in Milwaukee, Wisconsin, he is a graduate of the U.S. Naval Test Pilot School and was selected to become a NASA astronaut in 2017. He holds a master's degree in Aeronautics and Astronautics from the Massachusetts Institute of Technology.

Both Chari and Maurer are more than half way through their six-month stay on the ISS.

Spacewalks are an important part of life on the space station. Also called an extravehicular activity (EVA), a spacewalk is when an astronaut or cosmonaut gets out of the ISS whilst wearing a pressurized and oxygenated space suit that protects them from the vacuum of space.

Spacewalks can be performed for a variety of reasons. Sometimes they involve replacing or repairing old equipment on the outside of the ISS; other times spacewalks are carried out as part of science experiments.

During a spacewalk, astronauts are tethered to the ISS so that they do not accidentally float away. Suits may also be fitted with a space jetpack called a SAFER, which astronauts can use to return to the ISS in the event that they are separated.

Some spacewalks do come with issues. In an interview with Newsweek last year, NASA astronaut Mike Fincke recalled how he had to cut a spacewalk short after his suit began leaking oxygen.

"We have an electronic system that tells us if things are wrong with your spacesuit and gives you warning lights and everything," he said. "I had no warning lights, but I knew something was wrong. And just at the point where I started to say this, our ground controllers in Russian, they said, 'Hey, what's going on with your spacesuit?'

"I said 'the oxygen gauge's moving. I don't know what's going on, there's no caution warning lights. I'm not comfortable with this, I think I might need to go inside.' And they said 'Yeah, we don't know what's going on either. You better come inside.'"

A NASA photo shows astronaut Rick Mastracchio on a spacewalk outside the ISS in August, 2007. Astronauts go on spacewalks to fix or install equipment on the space station or to carry out experiments. NASA/Getty