Alexei Leonov, the first human to conduct a spacewalk, has died, according to a statement from Russia’s Roscosmos space agency released today (Oct. 11).

Leonov died at the Burdenko Hospital in Moscow after a long illness, the Russian news agency ITAR-Tass reported. He will be buried at the Federal Military Memorial Cemetery on Oct. 15, the agency added.

Leonov conducted his historic spacewalk on March 18, 1965 as part of the Voskhod 2 mission. He was lucky to survive the experience. Although the Soviet Union kept the details of the mission under wraps, Leonov’s spacesuit inflated during the walk, oxygen levels in the spacecraft itself skyrocketed, and a landing went awry deposited the crew in Siberia.

“It was so quiet I could even hear my heart beat,” Leonov told a British news agency of his spacewalk long after the event. “I was surrounded by stars and was floating without much control. I will never forget the moment. I also felt an incredible sense of responsibility.”

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