Leonov floats through space at the end of a lifeline during the first spacewalk. (AP Photo)The Soviets had practiced the entire operation countless times on Earth. But actually opening the hatch hundreds of miles above our planet's surface must have been unimaginably nerve-wracking for Leonov. The astronaut told TIME photographer Marco Grob that one facet of the first spacewalk still stands out sharply in his memory."I remember the sound, this remarkable silence," he said. "You can hear your heart beat and you can hear yourself breathe. Nothing else can accurately represent what it sounds like when a human being is in the middle of this abyss."Below, stunning images of other astronauts who, in the five decades since Leonov opened the Voskhod hatch, have ventured into that same silent chasm in the name of science.
