The six-hour-and-40-minute excursion by ISS Expedition 69 cosmonauts Sergey Prokopyev and Dmitri Petelin, who are equipped with helmet cameras, got underway at 9:40 p.m. EDT.

"Spacewalkers Sergey Prokopyev and Dmitri Petelin are currently outside the space station working to move a radiator from the Rassvet module to the Nauka module," the International Space Station tweeted Tuesday night.

Cosmonaut Andrey Fedyaev is assisting with robotic activities from inside the ISS using the European Space Agency's robotic arm.

Prokopyev, who is wearing an Orlan spacesuit with red stripes, and Petelin, who is wearing a suit with blue stripes, have already made two previous attempts at the spacewalk. However, an attempt in November had to be aborted because of a failed spacesuit pump. Then in December, a Russian Soyuz spacecraft suffered a coolant leak, forcing the attempt to be called off again.

Tuesday night's spacewalk is the fourth of Prokopyev's career and the second for Petelin, according to NASA. It is the third spacewalk at the ISS this year and is the 260th spacewalk for the space station assembly, maintenance and upgrades.

NASA said Tuesday that the pair had gotten a good night's sleep while the rest of the ISS crew "continued cleaning biology research hardware, conducted an eye and brain study and serviced a pair of spacesuits."

"NASA Flight Engineers Frank Rubio and Stephen Bowen worked together Tuesday cleaning up the Cell Biology Experiment Facility (CBEF) located in the Kibo laboratory module," the agency said.

After Tuesday's walk, the pair are scheduled for two more excursions on April 25 and May 4.

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