NASA astronaut Reid Wiseman works outside the International Space Station during a spacewalk in October 2014.NASA / Reuters

There are six people in space, according to this handy tracker. Two of them are really, really in space: Scott Kelly and Kjell Lindgren are conducting their first-ever spacewalks, dangling by cords from the International Space Station as it hurtles around the Earth at more than 17,000 miles per hour.

The pair of NASA astronauts will spend six and a half hours performing maintenance work outside of the orbital station on Wednesday. The agency says Kelly, the expedition commander, and Lindgren, a flight engineer, donned pressurized spacesuits this morning to, among other tasks, install a thermal cover over a particle physics detector that has been attached to the ISS since 2011. It is the 189th spacewalk for the station, and the 32nd for Americans.

NASA is broadcasting it live:

Earth is visible below the astronauts’ arms as they maneuver tools and equipment in zero-G. NASA staffers back at mission control in Houston advise the astronauts as they work. “You guys are doing great,” a voice from Earth can be heard.

Spacewalks are painstakingly scripted before astronauts even get to the ISS. They’re rehearsed over and over again in a pool big enough to fit two space shuttles. After all, one tiny deviation from the plan—one mistake—can spell disaster.

For the astronauts, spacewalks are, for lack of a better world, awesome. As Charles Fishman wrote for the magazine earlier this year:

Nothing captures the strange contradictions of modern spaceflight as well as spacewalking—shoving off into space with only your wits and training, sealed into your one-person spacecraft. An EVA (extravehicular activity) is, for almost all astronauts, the ultimate professional challenge and the ultimate thrill ride. When you’re outside the station, you are literally an independent astronomical body, a tiny moon of Earth, orbiting at 17,500 miles an hour. When you look at Earth between your boots, that first step is more than 1 million feet down.

The spacewalk is the latest milestone in Kelly’s historic mission aboard the ISS. The astronaut is halfway through a 342-stay on the station, the longest for any American astronaut.

Another spacewalk for Kelly and Lindgren is scheduled for November 6.

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