Its still the most exciting moment for any space voyager: A hatch opens, and the space-suited astronaut emerges into the deadly vacuum of space. The bold adventure we call spacewalking is 35 years old. And in all those years, it hasnt failed to provide moments of breathtaking beauty, high drama, and even nail-biting anxiety.

The world was stunned by the news of Alexei Leonovs brief excursion outside Voskhod 2 in March 1965. Suddenly, something that had only existed in science-fiction tales was real. For NASA, it was a stinging defeat: Spacewalks had been slated for the upcoming two-man Gemini flights, but the Soviets had once again upstaged the Americans plans.

In his stiff, pressurized spacesuit, Cernan became so overheated that his visor clouded over with moisture. Barely able to see, he aborted his spacewalk and struggled to find his way back into Gemini 9. NASA realized that Ed Whites weightless "romp" had been misleading: Spacewalking could be very difficult, even exhausting.

Two more Gemini spacewalkers, Mike Collins and Dick Gordon, confirmed that harsh reality. Not until the final Gemini mission did NASA conquer the spacewalk gremlins. Using a system of handholds and restraints, Buzz Aldrin was able to work for hours outside Gemini 12 with almost no difficulty.

By the late 1960s, walking in space had become more than an experiment. For both the Americans and the Soviets, it was a way to test key techniques and equipment for planned missions to the moon. In January 1969 cosmonauts Yevgeni Khrunov and Alexei Yeliseyev left their crewmate in Soyuz 5 and transferred to Soyuz 4, where they joined another waiting cosmonaut for the trip back to Earth. The Soviets hoped to use that technique during their lunar voyages -- but those flights never took place.

Several weeks later, U.S. astronaut Rusty Schweickart spent about half an hour outside Apollo 9 in Earth orbit, testing a new spacesuit designed to be worn on the moons surface. NASA had learned from the difficulties experienced by Geminis spacewalkers; the Apollo suit offered much greater ease of motion and a more efficient system to keep the wearer cool while working. And it worked beautifully in a spectacular and alien setting: Twelve moonwalkers used that design, or a variant of it, during the first explorations of another world.

And the last three Apollo missions showed that spacewalking could be even stranger than moonwalking. On the way back to Earth, the command module pilots of Apollos 15, 16 and 17 ventured into the eerie sunlit blackness to retrieve cassettes of scientific film from the side of the spacecraft. Those spacewalkers described a truly science-fiction experience: In one direction, they could see the Earth as a little ball suspended in the void; in the other, the world they had just explored -- the moon -- bid a silent farewell.

If Apollo took spacewalking to new heights -- literally -- then the next program, Skylab, made it even more daring, and more essential. During its launch on May 25, 1973, the Skylab space station was damaged by aerodynamic stresses. Skylab reached orbit, un-piloted, and missing one of its two solar-power arrays. The remaining array was lashed to the side of the station by a stray piece of metal.

For Pete Conrad and his crew, who reached Skylab 11 days later, the most critical assignment was to save the crippled station, including freeing the jammed solar array. On June 7 Conrad and Kerwin put on their spacesuits and went outside, where they assembled a pair of shears at the end of a long pole. Wielding their cutting tool, they managed to free the stuck array -- but not before Conrad and Kerwin, who had been pulling on the end of the array with a rope, went tumbling head-over-heels into space, until their umbilicals pulled them back to the station.

Two more Skylab crews demonstrated the many uses of a spacewalk as they retrieved scientific film, installed a sunshade on the stations hull, and even photographed Comet Kohoutek. Just as the later Apollo moonwalks had, the Skylab spacewalks lasted up to seven hours, a full workday in the vacuum of space.

In the 1980s, the art of spacewalking fully matured. For the Soviets, that happened aboard the Salyut and Mir space stations, whose crews spent months at a time in Earth orbit. Soviet spacewalkers did everything from repairing their stations propulsion systems to freeing stuck antennas. During their marathon missions, cosmonauts Leonid Kizim and Vladimir Solovyev logged nine spacewalks. With that kind of experience under their belts, cosmonauts were becoming the worlds champion spacewalkers.

Meanwhile, aboard U.S. space shuttles, astronauts were making spacewalking history of their own. In February 1984, Bruce McCandless became the first astronaut to test the Manned Maneuvering Unit -- and, in a moment reminiscent of Buck Rogers, an astronaut could fly freely in space, like a miniature spacecraft.

Impressive achievements followed. Shuttle spacewalkers captured wayward satellites and repaired them, or returned them to Earth. In 1993, after months of preparations on Earth, astronauts staged the most demanding space repair job ever when they fixed the ailing Hubble Space Telescope.

By that time, NASA was looking ahead to building a permanent International Space Station (ISS) in Earth orbit. In the 1990s shuttle spacewalkers practiced techniques they would put to use in building the ISS. During stays by U.S. astronauts aboard the Russian space station Mir, they and cosmonauts spacewalked together. It was a moment that would have been unthinkable when Alexei Leonov stepped into the void for a few brief, exhilarating minutes, 35 years ago.