A couple of spacewalking veterans floated outside the International Space Station Tuesday morning for the first of two planned spacewalks. NASA Flight Engineers Drew Feustel and Ricky Arnold emerged from the airlock at about 7:30 a.m. EST for a planned six-hour spacewalk. The day’s task: Moving a component called a Pump Flow Control Subassembly, or PFCS in space shorthand.

That component drives and controls the flow of ammonia through the station’s outdoor cooling system. And with six people living up there, 250 miles above Earth, no one wants all of those components and electronics overheating.

Robotics engineers who are not spacewalking are also involved in the mission. They’re controlling the big Canadarm2 and the Dextre robotic arm to place the PFCS on a truss for further testing.

For Feustel, this is the eighth spacewalk of his career. For Arnold, it’s his fourth.

It also happens to be the fiftieth spacewalk in the International Space Station program’s history.

This Sunday, anyone living in the region from Boston to Charleston will have a sky-watching opportunity to go outside and look up, and—weather permitting—see the next cargo trip heading up from Earth. At 5:04 a.m. EST, Orbital ATK’s Antares rocket will blast off from NASA’s Wallops, Virginia launch site, bringing up more than “7000 pounds of science and research to the space station in support of dozens of research investigations, as well as crew supplies and hardware,” NASA said.

That includes the components needed for the second of the spacewalks, happening in June.

The same astronauts, Feustal and Arnold, will again do the “outdoor work,” installing high-definition cameras on the Harmony module, which will make it easier for the future commercial crew vehicles to align with the international docking adapter.

Boeing and SpaceX are still planning to fly astronauts up to the space station later this year, with both aerospace companies aiming for their first test flights—flying up empty to prove they’re safe and sound—in August.

By next year, NASA will no longer have to rely on paying the Russian space program for $70 million a seat rides up into space.