First Spacewalk by Alexei Leonov: Why It Was a Secret

March 18, 2015 11:30 AM EDT

When the first man walked in space, almost nobody knew that it was happening.

Cautious about counting their cosmonaut before he was through the hatch, Soviet space officials kept the plan quiet until after success had been achieved. Aleksei Leonov had already safely returned to the Voskhod II spacecraft — 50 years ago today, on March 18, 1965 — before the Soviet space agency announced that he had left the ship and released photos and video of what had happened. (These days, the English spelling of the cosmonaut’s first name is more frequently “Alexei”; in 1965, however, this magazine spelled it with a “ks.”) The shots showed Leonov emerging from the craft’s hatch before turning a few somersaults to begin his 20 minutes in the nothingness.

The news wasn’t a complete surprise for the rest of the world, however. As TIME explained, U.S. radars had been following the Voskhod II and noticed, via a change in reflectivity, that a hole had opened in the craft. They also knew that Soviet ships were big enough and sturdy enough to accommodate several cosmonauts and the necessary equipment and airlock for a spacewalk. (American spaceships of the time had to be lighter, as the U.S. had not developed booster technology to lift spacecraft as heavy as the Soviets’.) The exact technology used by Leonov remained a mystery for the time being — for example, was the cord that tethered him to the ship a mere leash, or an “umbilical” connection for air or communications?

Still, even the USSR’s Cold-War enemies couldn’t help but admire the feat. As TIME reported, the following week, it was a momentous occasion for all humankind:

Tied to a capsule by a 16-ft. tether, the first human satellite whirled through the vacuum of space at 18,000 m.p.h.

For ten minutes Soviet Cosmonaut Aleksei Arkhipovich Leonov drifted and spun through dreamlike gyrations while he followed the spaceship Voskhod II in its swift, elliptical path around the distant earth. Then, as easily and efficiently as he had emerged from his ship, Leonov climbed back inside. After 15 more orbits, he and his comrade, Colonel Pavel Ivanovich Belyayev, began the long flight home.

With that brief solo excursion into hostile emptiness last week, Lieut. Colonel Leonov took man’s first tentative step down the long and dangerous track that he must travel before he truly conquers space. Circling the earth in a sealed and well-provisioned capsule has been demonstrated to be well within human capabilities, but the moon will never be explored, to say nothing of Mars and the other planets, unless fragile men learn to function in the outside vacuum where no earthborn organisms are naturally equipped to live.

Leonov’s short “stroll” into personal orbit was one of the most remarkable achievements of the remarkable age of space.

Read the full story, here in the TIME Vault: Adventure into Emptiness