A History of Spacewalking

From a Perilous Leap to Building Worlds in the Void

Extra-Vehicular Activity, or EVA, is the term for any activity done by an astronaut or cosmonaut outside a spacecraft, beyond the Earth’s appreciable atmosphere. It’s more commonly known as a “spacewalk.” This simple term fails to capture the complexity, danger, and sheer audacity of the endeavor. An EVA is not a walk. It is a one-person ballet in a hostile void, a delicate and dangerous operation where the astronaut becomes a living spacecraft.

A spacesuit is not an article of clothing; it is a custom-fit, multi-layer, pressurized vehicle. It provides life support, oxygen, temperature control, and protection from radiation and micrometeoroids, all while the astronaut inside attempts to perform useful work. Every EVA is a high-stakes event, a test of human ingenuity, training, and courage against the most unforgiving environment imaginable.

The history of EVA is the history of human expansion into space. Without it, we would be mere passengers, sealed inside our metal cans, observing the universe through a porthole. With it, we became active participants. We have been ableto repair our ships, build our orbital outposts, retrieve our science, and set foot on another world. This is the story of how we learned to leave the ship and work in the cosmos.

The Theoretical Dream

Long before the first rockets breached the atmosphere, thinkers were already imagining what humanity would do once it arrived. The Russian “father of cosmonautics,” Konstantin Tsiolkovsky, writing at the turn of the 20th century, conceptualized not just multi-stage rockets but also the experience of living in microgravity. He theorized about orbital space stations and the need for humans to exit their vessels, clad in “diving suits” for the vacuum.

For decades, this remained purely in the realm of science fiction. The engineering challenges were immense. The vacuum of space is a complete absence of pressure. Without protection, a human body’s fluids would boil away in seconds. The temperature swings are extreme, from hundreds of degrees in direct sunlight to hundreds below in shadow. Radiation from the sun and deep space is a constant threat. And then there was the unknown of microgravity itself. How could a person “move” without traction? How could they turn a wrench if turning the wrench also turned them?

In the early 1960s, as the Space Race between the United States and the Soviet Union accelerated, these questions moved from theoretical to practical. Both nations were pushing toward a lunar landing. They knew that to get to the Moon, they would first have to master rendezvous and docking in Earth orbit. And if something went wrong, or if a craft needed to be inspected, someone might have to go outside.

The First Perilous Steps

The competition to be the first was intense. The Soviet Union‘s Voskhod programme was designed to achieve a series of “firsts,” and the first spacewalk was high on their list. They built a stripped-down, two-person version of their Vostok capsule, adding an inflatable airlock to the side.

Leonov’s Frightening First

On March 18, 1965, cosmonaut Alexei Leonov was attached to a 17-foot tether and exited the Voskhod 2capsule. He became the first human to float freely in space. For 12 minutes, he was ecstatic, tumbling and turning against the blackness. He later described feeling like a bird, soaring with the Earth scrolling past below him at 17,000 miles per hour.

The triumph almost turned into a disaster.

His spacesuit, the Berkut, was a pure-oxygen, ventilation-based system. In the vacuum, the suit’s internal pressure caused it to balloon. It became stiff and unyielding. Leonov’s hands had pulled away from the gloves, and his feet from the boots. He was, as he later described, like a man inside an inflated rubber doll. When it was time to re-enter the narrow, tube-like airlock, he discovered he couldn’t. He was too wide.

He couldn’t get his feet in first as planned. He tried to go in head-first, but he still couldn’t bend his body enough to get through the hatch. His body temperature was soaring, and his heart rate was dangerously high. He was in danger of heatstroke, all while his partner, Pavel Belyayev, watched helplessly from inside.

In a desperate, un-scripted move, Leonov opened a valve on his suit and began bleeding his precious air pressure, lowering it to a level that was dangerously low in oxygen. The suit softened, and he was able to force himself head-first into the airlock, struggling to close the hatch behind him. He was drenched in sweat, having lost 13 pounds, and was on the verge of passing out. The first EVA was a success, but it was a terrifying, near-fatal experience that highlighted the significant dangers of working in space. The Voskhod 2 mission’s problems were far from over – an automated re-entry system failed, forcing a manual landing that left the crew stranded in the remote Ural mountains for two days – but Leonov had proven it was possible.

America’s Answer: Ed White

Less than three months later, on June 3, 1965, the United States followed. During the Gemini 4 mission, astronaut Ed White opened the hatch of his capsule. His EVA was a different experience. He was connected to his commander, Jim McDivitt, by a 25-foot gold-taped tether that also supplied his oxygen.

White’s G4C suit was an improvement over Leonov’s. He also had a small, hand-held maneuvering unit, a “zip gun” that expelled bursts of compressed gas. He used it to propel himself around, though he found it hard to control. Unlike Leonov’s near-panic, White’s 20-minute EVA was one of pure exhilaration. His communications back to Earth were filled with wonder. “I’m not coming in,” he joked at one point, floating weightless against the backdrop of the Gulf of Mexico.

His return to the capsule was not without its own drama. The hatch was difficult to close and latch, a problem that would plague the Gemini program. It took both men, exhausted and straining, to finally secure it. But White was back inside safely. The U.S. had shown it could also perform EVAs.

The Problem with Spacewalks

The “walks” by Leonov and White weren’t really work. They were tests of survival, “stay-alive” demonstrations. The real challenge, as NASA soon discovered, was working in space. And it was much, much harder than anyone had anticipated.

The problem became apparent on Gemini 9A in June 1966. Astronaut Gene Cernan was tasked with a complex, two-hour EVA. He was supposed to go to the back of the Gemini capsule, strap into a jetpack called the Astronaut Maneuvering Unit (AMU), and fly untethered.

It was a disaster.

Weighing 160 pounds on Earth, the AMU was a bulky backpack. In orbit, it was weightless, but it still had mass and inertia. Cernan, floating in the void with no handholds, had nothing to brace against. Every time he tried to pull on a strap or turn a valve, his body would spin in the opposite direction. He was fighting his own suit, which was stiff and clumsy.

Worse, his helmet’s life support system couldn’t handle the workload. As Cernan struggled, his body heat and perspiration overwhelmed the system. His visor fogged up, completely blinding him. He was hot, exhausted, and couldn’t see. He described it as “the spacewalk from hell.” The EVA was cut short. Cernan had been unable to even don the jetpack, let alone fly it.

Similar problems plagued Gemini 10 and Gemini 11. Astronauts were returning from EVAs utterly exhausted, their suits filled with sweat, having achieved only a fraction of their objectives. It became clear that Newton’s third law (for every action, there is an equal and opposite reaction) was a brutal tyrant in microgravity. Without leverage, simple tasks were impossible. NASA was facing a serious problem. If astronauts couldn’t perform basic work in Earth orbit, the Apollo program‘s goal of landing on the Moon was in jeopardy.

Solving the Puzzle

The man who solved the EVA puzzle was Buzz Aldrin. An MIT-trained engineer, Aldrin was assigned to Gemini 12, the final mission of the program. He didn’t just train for his spacewalk; he reverse-engineered the problem of spacewalking.

He realized the issue was leverage. He also championed a new training technique: underwater training. By weighting an astronaut in a spacesuit so they are neutrally buoyant in a large pool, engineers could simulate the weightlessness of space. It wasn’t a perfect simulation – water has drag, and objects don’t stay put as they do in orbit – but it was the best tool they had.

Aldrin spent hours in the pool, practicing every move. He discovered that slow, deliberate motions were key. He also advocated for the outside of the spacecraft to be designed for EVA. NASA listened, adding simple handholds, foot restraints, and tethers to the Gemini 12 capsule.

Aldrin’s two “stand-up” EVAs and one tethered EVA on Gemini 12 were a stunning success. He performed tasks with ease, moving along the capsule, using the new handholds and “golden slippers” (foot restraints) to anchor himself. He connected and disconnected cables. He used a torque wrench. He proved, definitively, that a human could work in space. The lessons learned from Aldrin’s EVAs – underwater training, proper restraints, and slow, deliberate movements – became the foundation for all future spacewalks.

Walking on Another World

The Apollo program presented a new, unique challenge. Astronauts wouldn’t be floating in microgravity; they would be walking, working, and driving in the one-sixth gravity of the Moon. This required an entirely new type of spacesuit.

The Suit for the Moon

The A7L spacesuit was a marvel of engineering. Unlike the Gemini suits, which were connected to the capsule’s life support, the Apollo suit was a self-contained spacecraft. It had to be. On the lunar surface, the astronauts would be untethered, hundreds of thousands of miles from home.

The suit’s “backpack,” the Portable Life Support System (PLSS), was its most impressive feature. It provided seven hours of oxygen, removed carbon dioxide, circulated cooling water through a body-hugging undergarment, and housed the radio communications.

The suit itself was a complex, 21-layer garment. It had a pressure bladder to hold the oxygen, a restraint layer to keep the suit from ballooning, and outer layers of Mylar and Beta cloth to provide thermal and micrometeoroid protection. The boots were designed with special soles for walking on dusty, unknown terrain.

This new suit was first tested in Earth orbit on Apollo 9 by astronauts Rusty Schweickart and Dave Scott. Schweickart performed an EVA, climbing out of the Lunar Module (LM) and testing the PLSS. The test was a success, clearing the suit for the Moon.

One Giant Leap

On July 20, 1969, Neil Armstrong descended the ladder of the Apollo 11 LM Eagle. He dropped onto the footpad and made the most famous statement of the 20th century: “That’s one small step for [a] man, one giant leap for mankind.”

He was followed by Buzz Aldrin. Their EVA lasted just two and a half hours, but it was a dense, heavily scripted series of tasks. They tested their mobility, finding a loping, skipping gait was the most effective way to move in the 1/6th gravity. They planted the American flag, collected 47 pounds of lunar rocks and soil, set up a seismometer and a laser reflector (the Lunar Laser Ranging experiment), and took a phone call from the President.

Their A7L suits performed beautifully, though the lunar dust, a fine, abrasive powder, was already proving to be a nuisance, clinging to everything. They returned to the LM, repressurized the cabin, and prepared for their historic rendezvous with Michael Collins in the Command Module orbiting above.

The Lunar Geologists

The later Apollo missions expanded on this first step, turning lunar EVA into a powerful tool for scientific exploration. The “J-missions” – Apollo 15, Apollo 16, and Apollo 17 – were true geological expeditions.

These missions featured upgraded suits with better mobility and longer-duration life support. Most importantly, they carried the Lunar Roving Vehicle (LRV), an electric “moon buggy.” The LRV revolutionized lunar EVA. Astronauts were no longer limited to how far they could walk from the LM. They could now drive for miles, venturing to canyons, mountains, and craters.

The EVAs became marathons. On Apollo 17, astronauts Gene Cernan and Harrison “Jack” Schmitt (the only geologist to walk on the Moon) spent over 22 hours outside on three separate EVAs. They drove the rover 22 miles, collected 243 pounds of samples (including the famous orange soil), and set up complex experiments.

These EVAs weren’t just about planting flags; they were about doing hard science in the most extreme laboratory imaginable. The Apollo astronauts proved that humans could be effective field scientists on another world.

The Loneliest Spacewalk

Not all Apollo EVAs happened on the Moon. Three of them took place in the vast, empty expanse of cislunar space, on the return journey to Earth.

The Apollo Command/Service Module carried mapping cameras and scientific instruments in its Service Module. To retrieve the film canisters, the Command Module Pilot had to perform a “deep space” EVA.

On Apollo 15, Al Worden performed the first such EVA. While 196,000 miles from Earth, he exited the Command Module, his feet locked in restraints, and pulled himself hand-over-hand along the side of the Service Module to the instrument bay. His only tether connected him to his crewmate, Jim Irwin, who stood in the open hatch.

As Worden worked, he had a view unlike any other in history. In one direction, he could see the full, round Earth, a “blue marble” in the blackness. In the other direction, he could see the Moon he had just left, a receding crescent. He was a solitary human figure, suspended between two worlds. This feat was repeated by Ken Mattingly on Apollo 16 and Ron Evans on Apollo 17. To this day, they remain the only humans to have performed EVAs in deep space.

Living and Working in Orbit

After the Apollo program ended in 1972, the focus of human spaceflight returned to Earth orbit. The new goal was to build and live on space stations, and EVAs would be essential for their construction and maintenance.

The Heroic Repair of Skylab

In May 1973, NASA launched Skylab, America’s first space station. The launch was a near-catastrophe. During ascent, the station’s micrometeoroid shield ripped away, taking one of its two main solar arrays with it. The other array was jammed shut by debris.

Skylab was in orbit, but it was crippled. It had almost no power, and without its sun shield, temperatures inside were soaring to uninhabitable levels.

The first crew, led by Pete Conrad, launched 10 days later on a rescue mission. Their first task was a “fly-around” inspection. Astronaut Paul Weitz tried a “stand-up” EVA from the Apollo capsule’s hatch, attempting to free the jammed solar array with a long pole, but it wouldn’t budge.

After docking, the crew entered the sweltering station and, on their first full day, performed a difficult EVA. They deployed a makeshift “parasol” sunshade through a scientific airlock, successfully cooling the station.

The real challenge came 12 days later. Conrad and Joseph Kerwin ventured outside. Their target was the jammed solar array. Tethered to the station, Conrad used a pair of long-handled cable cutters, like a giant pair of gardening shears, attached to a 25-foot pole. He had to sever the piece of metal debris pinning the array.

It was brutal, exhausting work. Conrad, bracing himself, struggled to get enough leverage. Finally, he attached a tether to the array and, with Kerwin pulling on the tether from inside the station’s airlock, they managed to break the array free. It snapped open, deployed, and power began flowing to the station.

The Skylab rescue was one of the most important EVAs in history. It proved that complex, unplanned repairs could be performed in orbit. It demonstrated that humans weren’t just visitors in space; they were mechanics who could fix their own ships. Subsequent Skylab crews would conduct multiple EVAs to retrieve film, service experiments, and perform more repairs.

The Soviet Mainstay: Salyut and Mir

The Soviets, meanwhile, were focusing on their Salyut programme of orbital stations. They developed a new, robust spacesuit: the Orlan spacesuit.

The Orlan had a different design philosophy from the American suits. It was “semi-rigid,” with a solid hard-torso and flexible arms and legs. This made it more durable and, most importantly, easier to put on. An astronaut didn’t “wear” an Orlan; they “entered” it through a hatch in the back. This “rear-entry” design allowed a cosmonaut to suit up without assistance in about five minutes, a process that took hours in the American suit.

The Orlan became the workhorse of the Soviet and later Russian space program. It was used for maintenance on the Salyut stations, and it’s where the next major EVA milestone occurred. On July 25, 1984, Svetlana Savitskaya, flying on Salyut 7, became the first woman in history to perform a spacewalk. During her 3.5-hour EVA, she and a fellow cosmonaut tested tools for welding, cutting, and soldering metals in the vacuum of space.

The Orlan’s finest hour came with the Mir space station. Launched in 1986, Mir was the first modular space station. New modules were added over the years, and nearly all this assembly work required EVAs. Cosmonauts on Mir became old hands at spacewalking, performing complex EVAs to install new solar arrays, move equipment, and conduct repairs. When a cargo ship collided with the Spektr module in 1997, cosmonauts performed a harrowing “internal” EVA – a spacewalk inside the depressurized, damaged module – to try and restore power.

The Shuttle Era: The Satellite Doctors

In 1981, NASA’s Space Shuttle program began. The shuttle was a reusable space plane with a massive cargo bay, and it ushered in a new era of routine EVA.

The EMU and the MMU

For the shuttle, NASA developed the Extravehicular Mobility Unit (EMU). Like the Apollo suit, it was a self-contained spacecraft. Unlike the Apollo suit, it was modular. It consisted of a hard upper torso, a lower torso, and arms, which could be assembled in different combinations to fit different astronauts. This made it more flexible and cost-effective than building custom suits for every person.

The shuttle also introduced the most iconic (and, for a time, most futuristic) piece of EVA hardware: the Manned Maneuvering Unit (MMU). This was the jetpack Gene Cernan had failed to test. It was a bulky armchair-like backpack that used small nitrogen-gas thrusters, controlled by the astronaut’s right hand, to allow for untethered flight.

On February 7, 1984, during mission STS-41B, astronaut Bruce McCandless II strapped on the MMU and pushed away from the shuttle. He became the first human satellite, flying completely untethered, propelled only by his jetpack. The photograph of his tiny, white-suited figure floating alone against the blackness of space, with the blue Earth far below, is one of the most famous images of human exploration. He flew 300 feet from the shuttle, a small act of flight that represented an enormous level of confidence in the technology.

The Great Rescues

The MMU wasn’t just for joyriding; it was a tool. The shuttle’s main promise was the ability to not just deploy satellites, but to service them in orbit. This was put to the test on STS-41C in April 1984, just two months after McCandless’s flight.

The Solar Maximum Mission (SolarMax) satellite had failed, and NASA was going to fix it. Astronaut George “Pinky” Nelson, wearing the MMU, flew over to the slowly spinning satellite. His plan was to dock with it using a special capture tool. But the tool failed to latch. Every time he tried, he inadvertently pushed the satellite, increasing its spin. The MMU plan was abandoned.

The crew improvised. Shuttle commander Robert Crippen painstakingly maneuvered the 100-ton shuttle to within feet of the satellite, and his mission specialist, Terry Hart, grabbed it with the Canadarm (the shuttle’s robotic arm) and placed it in the cargo bay. Nelson and James “Ox” van Hoften then performed a marathon EVA, replacing the satellite’s failed attitude-control module and electronics. SolarMax was redeployed, fully functional.

An even more audacious mission followed in November 1984. STS-51A was sent to retrieve two communications satellites, Palapa B2 and Westar 6, that had been deployed into useless orbits.

Astronaut Joseph Allen, using the MMU, flew to the Palapa satellite. He and Dale Gardner had practiced for this. Allen grabbed the satellite by hand, stabilized it, and held it while the shuttle’s arm grappled it and lowered it into the bay. Gardner, using a specially designed “stinger” attachment, latched onto the Westar satellite. At one point, Gardner and Allen were both in the cargo bay with their captured satellites. Gardner later held up a hand-painted “For Sale” sign, a joke that captured the “can-do” spirit of the era.

These “satellite doctor” missions were the high point of shuttle-based EVA. After the Challenger disaster in 1986, safety reviews led to the retirement of the MMU. It was deemed too risky. Future EVAs would be tethered, but the new standard of safety was a small, compressed-gas jetpack worn by U.S. astronauts called SAFER (Simplified Aid for EVA Rescue). It’s an emergency device, a “lifeboat” to allow an astronaut who becomes untethered to fly back to safety.

The Age of Assembly and Repair

The 1990s and 2000s saw EVA shift from retrieval to two massive projects: saving the world’s most famous telescope and building the largest structure ever put in space.

Saving Hubble (Again and Again)

When the Hubble Space Telescope was deployed in 1990, it was a public relations disaster. Its images were blurry. The telescope’s main mirror had a tiny, but devastating, flaw – a spherical aberration.

The telescope had been designed from the ground up to be serviced by spacewalking astronauts. In December 1993, the crew of STS-61 flew an incredibly complex repair mission. It was one of the most ambitious EVAs ever planned.

Over five consecutive days, two teams of astronauts – Story Musgrave (a veteran of the first shuttle EVA), Jeff Hoffman, Kathy Thornton, and Tom Akers – performed five EVAs totaling 35 hours. They were performing brain surgery in orbit.

They installed COSTAR, a set of “contact lenses” to correct the flaw. They replaced the Wide Field and Planetary Camera with a new version that had its own built-in corrective optics. They replaced solar arrays and gyroscopes. The mission was a flawless success. The first images from the repaired Hubble were sharp, clear, and breathtaking.

This was just the beginning. Four subsequent servicing missions (SM2, SM3A, SM3B, and SM4) would see astronauts return to Hubble to upgrade its instruments, giving it new life and new capabilities. The final mission in 2009, STS-125, was particularly dramatic. Astronaut Mike Massimino had to use brute force to break off a handrail with a stuck bolt just to get a cover off, a moment of unscripted ingenuity that saved a key instrument. The Hubble EVAs stand as the single greatest testament to the value of humans in space, transforming a failure into one of the most productive scientific instruments in history.

Building the International Space Station

While Hubble was being repaired, a new project was beginning. The International Space Station (ISS) is the largest, most complex, and most expensive object ever built by humanity. And it was built, piece by piece, by spacewalkers.

The first ISS assembly EVA took place during STS-88 in December 1998. Astronauts Jerry Ross and Jim Newman connected data and power cables between the first two modules, the American Unity node and the Russian Zarya module.

Over the next two decades, this scene would be repeated over 200 times. Astronauts and cosmonauts from the U.S., Russia, Europe, Japan, and Canada would venture outside. They installed the station’s massive 240-foot-long truss, unrolled its football-field-sized solar arrays, and attached new laboratory modules.

The Canadarm2, the station’s advanced robotic arm, became an essential EVA tool. It acted as a mobile platform, a “cherry picker” that could move an astronaut on its end to precise locations, eliminating the need for long, tedious hand-over-hand climbing.

The Most Dangerous Repairs

Life on the ISS wasn’t just construction; it was also maintenance. And sometimes, that maintenance was terrifying.

In 2007, during STS-120, a newly deployed solar array tore, creating a “live” wire of 100 volts and threatening the station’s power supply. On an emergency EVA, astronaut Scott Parazynski was sent to fix it. The tear was too far to reach, so the crew attached the shuttle’s 50-foot inspection boom to the station’s 57-foot robotic arm, creating a 100-foot-long contraption.

Parazynski rode on the end of the boom, which was maneuvered to within inches of the energized array. He had to be “hands-off,” using insulated tools to “sew” the panel back together with homemade “cufflinks.” It was one of the most dangerous and delicate repairs ever attempted.

An even more complex repair occurred between 2019 and 2020. The Alpha Magnetic Spectrometer (AMS), a $2 billion particle physics experiment, was failing. It was never designed to be serviced. But losing it was not an option.

Engineers on the ground designed new tools and procedures from scratch. Over a series of four complex EVAs, astronauts Andrew Morgan and Luca Parmitano performed what was compared to open-heart surgery. They cut and spliced cooling tubes, removed old components, and installed a new thermal pump system, saving the experiment.

Milestones in Orbit

The ISS era has seen its share of historic firsts. On October 18, 2019, NASA astronauts Christina Koch and Jessica Meir performed the first all-female spacewalk. The milestone, which had been delayed months earlier due to a lack of a medium-sized hard torso on the station, highlighted both the progress women had made in the space program and the persistent logistical challenges of EVA.

A near-disaster also occurred in 2013, when Luca Parmitano‘s helmet began filling with water from his cooling suit, a terrifying incident that forced an emergency termination of the EVA. He was nearly blinded and drowned, but made it back to the airlock safely. The incident led to a full investigation and redesign of the suit’s water separator.

The Technology of Spacewalking

Decades of experience have refined the tools and techniques of EVA, but the fundamental challenges remain.

The Spacesuit: A Personal Spacecraft

A modern spacesuit like the EMU or Orlan is a masterpiece of engineering. It’s composed of multiple layers, each with a specific job:

• Liquid Cooling and Ventilation Garment (LCVG): The innermost layer, worn against the skin. It’s a full-body-garment, like long underwear, threaded with 300 feet of thin plastic tubing. Cool water circulates through it to draw away body heat.
• Pressure Bladder: A urethane-coated nylon layer that holds the pressurized oxygen.
• Restraint Layer: A Dacron layer that surrounds the bladder, giving the suit its shape and keeping it from ballooning.
• Thermal Micrometeoroid Garment (TMG): The outer, white layer. It’s a sandwich of multiple layers, including aluminized Mylar for thermal insulation and an outer layer of blended Gore-Tex, Kevlar, and Nomex to protect against small debris.

The “backpack” (the PLSS for the EMU) contains the oxygen tanks, a fan for circulating air, a lithium hydroxidefilter to scrub carbon dioxide, a water pump, batteries for power, and a radio.

The gloves remain the hardest part to design. They must be pressurized and protective, yet flexible enough for astronauts to operate tools and feel small objects. Astronauts often return from long EVAs with bruised or missing fingernails, a testament to the strain of working inside stiff, pressurized gloves.

A Comparison of Key Spacesuits

The evolution of the spacesuit tells the story of EVA’s changing needs, from simple survival to complex construction.

The Perils of the Void: Decompression

One of the greatest medical risks of an EVA is decompression sickness, or “the bends.”

The ISS, like a passenger jet, is pressurized to Earth’s sea-level pressure, about 14.7 pounds per square inch (psi). This is a comfortable, “mixed-gas” atmosphere of nitrogen and oxygen. A spacesuit operates at a much lower pressure. The U.S. EMU, for example, operates at 4.3 psi of pure oxygen.

Why the difference? A high-pressure suit would be almost impossible to move. A 14.7 psi suit would be as rigid as a car tire. The 4.3 psi is a compromise, providing enough oxygen to breathe while maintaining flexibility.

But this pressure difference is dangerous. It’s the same problem scuba divers face when ascending too quickly. The nitrogen dissolved in the astronaut’s blood and tissues can form bubbles if the pressure drops too fast, causing joint pain, neurological damage, or even death.

To prevent this, astronauts must go through a “pre-breathe” protocol. Before an EVA, they spend hours breathing pure oxygen to “wash” the nitrogen out of their bodies. A common method involves a “campout” in the Quest Joint Airlock, where the pressure is lowered to 10.2 psi the night before the spacewalk, accelerating the process. This pre-breathe is a time-consuming but essential safety step.

Training for Nothingness

You can’t practice for an EVA in space. By the time the hatch opens, you must be a master. This mastery is achieved on Earth, in the world’s largest swimming pools.

NASA’s primary training facility is the Neutral Buoyancy Laboratory (NBL) at the Johnson Space Center in Houston. The NBL is a gigantic pool, 202 feet long, 102 feet wide, and 40 feet deep, holding 6.2 million gallons of water. It contains full-scale, high-fidelity mockups of the International Space Station.

Astronauts, wearing training versions of their spacesuits, are carefully weighted by scuba divers to be neutrally buoyant – neither sinking nor floating. This is the closest simulation of microgravity on Earth. For every one hour of EVA they are scheduled to perform in space, astronauts will spend about seven hours training in the pool.

It’s grueling work. The suits are clumsy, and water drag is a constant, frustrating force that doesn’t exist in space. But it’s where they learn the procedures, practice with the tools, and memorize the “choreography” of the spacewalk. Russia‘s Gagarin Cosmonaut Training Center in Star City has a similar facility, the Hydrolab.

The New Guard: China and Commercial Space

The U.S. and Russia are no longer the only players in the EVA game.

China’s Celestial Walk

On September 27, 2008, China became the third nation to independently conduct an EVA. As part of the Shenzhou 7 mission, “taikonaut” Zhai Zhigang exited his capsule wearing a Chinese-built Feitian spacesuit. The Feitian is heavily based on the Russian Orlan, featuring a semi-rigid design and a rear-entry hatch.

Since then, China has made rapid progress. EVAs have been a routine and essential part of the construction of their Tiangong space station. In November 2021, Wang Yaping became the first female Chinese spacewalker, conducting an EVA outside the station.

The First Commercial Spacewalk

The domain of EVA is also expanding from government agencies to the private sector. The Polaris Dawn mission, a private mission financed by Jared Isaacman and operated by SpaceX, conducted the first-ever commercial spacewalk in 2024.

Flying in a SpaceX Dragon 2 capsule, the crew depressurized the entire capsule and opened the outer hatch. Two astronauts, Isaacman and Sarah Gillis, partially exited the craft while tethered, wearing new EVA suits developed by SpaceX. This “stand-up” EVA, the first of its kind since the Gemini program, was a test of the new suit and a stepping stone toward more complex commercial EVAs in the future.

The Future of EVA

The future of spacewalking is focused on returning to the Moon and, eventually, going to Mars. Both present new challenges.

Back to the Moon with Artemis

NASA’s Artemis program aims to land the first woman and first person of color on the Moon. These new lunar explorers will require a new generation of spacesuits.

The U.S. is taking a commercial approach. NASA has contracted with two companies, Axiom Space and Collins Aerospace, to develop the suits for Artemis missions and for future work on the ISS.

These suits must be far more advanced than the Apollo-era A7L. They need to accommodate a wider range of body types. They must provide far greater mobility, especially in the lower body, to allow astronauts to walk, crouch, and kneel. And they must solve the problem of lunar dust.

The fine, abrasive lunar regolith was a major problem for Apollo astronauts. It clogged mechanisms, destroyed seals, and caused “lunar hay fever” when brought inside the capsule. The new suits will need to have advanced dust-mitigation systems to prevent this.

On to Mars

An EVA on Mars will be another beast entirely. The 3/8ths gravity is different from the Moon’s 1/6th. The dust is toxic. The communication delay with Earth will be up to 20 minutes each way, meaning spacewalkers must be completely autonomous, unable to ask for real-time help.

The suits will need to be even more robust, like miniature geological field-labs, with built-in diagnostics and repair capabilities. Some concepts, like the Bio-Suit, propose using mechanical counterpressure – a skintight suit that squeezes the body – to avoid the problems of a gas-pressurized suit altogether.

Summary

The history of Extra-Vehicular Activity is a story of incredible human adaptation. It began with Alexei Leonov‘s terrifying, near-fatal tumble, a leap into a void we did not understand. It evolved through the brutal lessons of the Gemini program, where astronauts learned that “work” in space required leverage and training. It reached its first pinnacle on the Moon, as Apollo astronauts bounded across an alien world.

Spacewalkers went on to become repair mechanics, saving Skylab and Hubble, and satellite retrievers in the shuttle era. Most recently, they have been construction workers, assembling the International Space Station, the largest home humanity has ever built off-planet.

Every EVA is a reminder that humans are not content to just observe. We have an unshakeable need to go outside, to touch, to fix, and to build. The spacesuit is the ultimate expression of that need. It’s the tool that allows us to project a fragile, 1G-evolved human body into the most hostile environment known, and to get the job done.