Space Welding: The Complete Guide to Welding in Orbit, Vacuum, and Beyond

On October 16, 1969, cosmonaut Valery Kubasov flipped a switch inside an unpressurized spacecraft and melted two pieces of metal together in the vacuum of space — while the rest of the world argued about the Moon landing. Fifty-plus years later, engineers are still trying to answer a deceptively simple question: how do you build, repair, and manufacture metal structures when there is no air, no gravity, and no second chance?

What Is Space Welding? Defining the Final Frontier of Fabrication

On October 16, 1969, cosmonaut Valery Kubasov flipped a switch inside an unpressurized spacecraft and melted two pieces of metal together in the vacuum of space. This landmark moment took place aboard the Soviet Soyuz-6 spacecraft, where the first welds in space were performed using the automated ‘Vulkan’ unit. Half a century later, that deceptively simple task is still one of the greatest hurdles facing the future of off-world construction. So, what exactly is space welding?

Defining Space Welding

In its simplest form, ‘space welding’ refers to fusion and solid-state joining processes that are carried out in environments far removed from a workshop floor. These can range from the vacuum of low Earth orbit (LEO), to the reduced gravity of the lunar surface, and all the way to the harsh conditions of deep space. Unlike the work carried out in a fabrication shop, space welding cannot rely on the comforts of Earth’s atmosphere. Instead, it must function in microgravity and a near-total vacuum, two factors that change the game entirely.

While the end goal of creating a strong, permanent bond is the same, the approach differs drastically from terrestrial methods. Processes that are commonplace back on Earth, such as those covered in guides on MIG welder setup, TIG welding sheet metal and even large-scale operations such as railroad thermite welding, are designed around air, gravity and abundant shielding resources. In orbit, all three are stripped away. With proper welding PPE and rigorous MIG welding safety precautions still vital on Earth, off-world fabrication must take that level of caution to an entirely new extreme.

A Fundamental Shift in Physics

The greatest challenge of space welding lies within its physics. On Earth, excess heat from a weld is lost through three methods: conduction, convection and radiation. In the vacuum of space, there is no surrounding gas to carry heat away, meaning that heat leaves a weld pool almost entirely by radiation. This causes drastically steeper thermal gradients and far different cooling rates, ultimately leading to microstructures that can vary wildly from their Earth-bound counterparts.

This vacuum also wreaks havoc with the arc itself. Without atmospheric pressure to contain it, arc behavior in vacuum can be unpredictable, often resulting in arc constriction, increased voltage, arc wander and metal vaporization at far lower temperatures due to depressed boiling points. As highlighted in NASA’s review of welding in space and related technologies, these factors alone are enough to render many traditional procedures unworkable. Most critically, weld pools in microgravity are shaped by surface tension (Marangoni flow), rather than buoyancy-driven convection. In layman’s terms, there is no ‘down’ for molten metal to fall to, causing it to behave less like a puddle on a steel plate, and more like a droplet floating in zero-g.

Who Is This For, and What to Expect

With such a niche topic, search intent for the keyword ‘space welding’ is mostly informational and curiosity-driven. However, it has a strong secondary audience of engineers and students looking to explore the metallurgy and engineering behind it. For those with an interest in the technical side of the trade, concepts such as joint preparation and procedure control will feel familiar to disciplines ranging from pipe welding procedures to selecting electrodes for stick welding.

Ultimately, space welding isn’t science fiction. It’s a proven, 50-year-old feat of engineering that still poses challenges to this day. By stripping away the variables that welders take for granted, it serves to highlight just how remarkable even the most basic weld can be, both here on Earth, and amongst the stars.

A Short History of Welding in Space: From Soyuz-6 to Today

Nobody believed it would work. On 16 October 1969, two months after Apollo 11, the Soviet Union launched Soyuz-6 with two cosmonauts, Valery Kubasov and Georgy Shonin, and a compact experiment unit called Vulkan. While the world argued about footprints in the Sea of Tranquility, Kubasov flipped a switch inside an unpressurized, unheated compartment behind the descent module and melted metal together in open space. It was the first time a human had welded outside an atmosphere, and it remains the most cited milestone in this field.

The Vulkan Experiments Aboard Soyuz-6 (1969)

Vulkan was not a single process but a small mobile workshop. It demonstrated three metal-joining and metal-cutting techniques in the vacuum of orbit: electron beam welding, brazing, and cutting. Roughly twenty experiments were planned; the three that ran produced samples sealed into the descent capsule and brought home for metallurgical analysis at the E.O. Paton Electric Welding Institute in Kyiv, which had designed the hardware.

The results calmed a lot of nerves. The electron beam welds were sound, with fine-grained fusion zones that compared favourably with identical joints made in ground vacuum chambers. The arc, later described by Kubasov, was startlingly visible: in orbit you can look straight at a welding arc in broad “daylight” because no sky washes it out, a fact that raised immediate questions about operator eye protection and camera exposure.

Why electron beam? Because vacuum is its native environment. On Earth, electron beam welding needs a chamber pumped down to a near-vacuum, which is expensive and slow. In orbit, the vacuum is free.

America Answers: NASA, the Paton Institute, and ISWE

The Vulkan flight lit a fuse. Through the 1970s and 1980s, NASA and the Paton Institute of Electric Welding collaborated on in-space joining research, an unusually open line of technical exchange during the Cold War. That work fed a serious hardware program: the In-Space Welding Experiment (ISWE), developed through NASA’s Marshall Space Flight Center for the planned Space Station Freedom. ISWE was designed to compare several processes in orbit — electron beam, gas metal arc, and resistance welding, the same physics behind every industrial spot welder. Ground vacuum-chamber testing went deep, then Freedom was descoped in 1993 and ISWE was cancelled before it flew: the first lesson that space welding programs die of budget politics more often than of physics.

Shuttle, Mir, and the ESA Era

The 1990s shifted the work from flight hardware to laboratories on both sides of the Atlantic. Russian and European experiments aboard Mir probed electron beam welding and cutting in weightlessness, while ESA researchers began systematic studies of how vacuum changes the mechanical behaviour of joined metals. Shuttle-era NASA work ran largely in thermal vacuum chambers at Marshall and Johnson, refining the thermal models engineers still use. By the early 2000s, attention had migrated to the ISS, where the question became less “can we weld?” and more “what will welded structures do over a twenty-year mission?”

The fiftieth anniversary of Soyuz-6 in 2019 triggered a wave of retrospectives, including a detailed technical history of the Vulkan program published by the Paton Welding Journal and NASA’s own summary reviews (Sowards, 2023; Naden, 2020). Those reviews confirmed an uncomfortable truth: in half a century, no human has welded in orbit since 1969.

Space Welding Timeline at a Glance

• 16 October 1969 — Soyuz-6 Vulkan unit performs electron beam welding, brazing, and cutting in open space.
• 1970s–1980s — NASA–Paton Institute joint research on in-space joining processes.
• 1988–1993 — In-Space Welding Experiment developed for Space Station Freedom, then cancelled in the station’s redesign.
• 1990s — Mir-based experiments and ESA vacuum-welding studies; extensive ground thermal-vacuum testing.
• 2019 — Fiftieth-anniversary retrospectives and renewed academic interest in orbital fabrication.
• 2020–2023 — NASA publishes updated reviews of welding in space and its open literature.
• 2023–2025 — ESA scrutinises space-made welds in its lab and reports on the first autonomous weld in orbit, against ground reproductions of the 1969 electron beam method (ESA).
• November 2024 — ASTROBEAT, an ISS National Laboratory-sponsored cold-welding demonstration, launches aboard SpaceX CRS-31 to test whether metal patches can bond to a simulated spacecraft hull without heat (ISS National Lab).

The next sections pick up where this timeline ends: why anyone pays for this, how the processes differ, and what a molten pool in weightlessness really looks like.

Why Weld in Space at All? The Case for Off-World Fabrication

Ask most people why anyone would bother welding in space and you’ll get a shrug — we already have rockets, robots, and the International Space Station. What’s actually missing? The answer comes down to a number that governs everything in spaceflight: kilograms. Every bolt, every truss segment, every gallon of propellant that leaves Earth has to be accelerated to roughly 28,000 km/h, and that makes launch mass absurdly expensive. Welding — the humble act of permanently joining two pieces of metal — is one of the few tools that can break that equation.

The Tyranny of Launch Mass

Launching hardware to low Earth orbit historically cost tens of thousands of dollars per kilogram, and even with reusable rockets driving prices down, mass remains the currency of mission design. That’s why spacecraft are folded, stacked, and packed like origami inside a rocket fairing. But there is a hard physical ceiling on this trick: a structure that doesn’t fit inside the fairing can’t launch, period. A 25-meter antenna, a mile-long truss for a Mars-bound transfer stage, or a solar array the size of a football field simply cannot ride to orbit whole.

Welding changes the arithmetic. Instead of launching a finished structure, you launch raw stock or modular segments and join them on orbit. That’s the founding logic behind NASA and the ISS National Lab’s long-running interest in in-space manufacturing and assembly, now a stated priority for both NASA and ESA as they build toward cislunar and lunar-surface infrastructure.

Repair Beats Replacement

The second big motivator is repair. Spacecraft are fragile. Micrometeoroids and orbital debris punch holes in hulls and damage propellant tanks, and a single puncture can end a mission worth billions. On Earth, the fix is obvious: strike an arc. In orbit, there is currently no way to patch a damaged aluminum fuel tank or pressure vessel in place — you can only cover it up and hope.

The same logic extends to on-orbit servicing. Communications satellites run out of propellant long before their electronics wear out. If a servicing robot could refuel, reposition, and structurally repair aging satellites, orbital assets could gain years of revenue instead of becoming expensive debris. Welding — or its solid-state cousins — is the enabling tool for that entire servicing economy.

In-Space Manufacturing: Materials That Only Microgravity Can Make

Here is where it gets genuinely exciting for engineers. On Earth, gravity ruins a lot of high-temperature materials work. During solidification, denser elements sink and lighter ones rise — a process called buoyancy-driven sedimentation. Bubbles float and convection currents stir the melt unevenly. Microgravity eliminates those effects, which means alloys can solidify with a homogeneity that is physically impossible on the ground, and crystals can grow larger and with far fewer defects.

That matters for high-performance electronics, fiber optics, semiconductor substrates, and specialty alloy research. The European Space Agency has leaned into this for years, and ESA continues to examine joints and materials produced in orbit to understand what vacuum-formed microstructures actually look like. If you already know how a weld solidifies on Earth — including the distortion and defect risks in our guide to weld undercut and other common defects — you have the vocabulary for these orbital metallurgy questions.

Building on the Moon (and Beyond)

The ultimate case is In-Situ Resource Utilization, or ISRU: using local materials to build infrastructure. Hauling habitat modules and landing pads from Earth to the lunar surface costs an enormous multiple of the same mass launched to orbit. The far cheaper path is to sinter regolith, extract metals from lunar soil, and weld or otherwise join them into shelters, berms, and launch surfaces right where you stand. Every structure built this way is mass you never had to launch — and that principle scales directly to Mars.

The Practical Payoff, Summarized

• Assemble the un-launchable: antennas, trusses, and solar arrays larger than any fairing can hold.
• Repair in place: hull breaches, tanks, and radiators patched instead of abandoned.
• Extend satellite life: on-orbit servicing turns single-use assets into long-lived infrastructure.
• Manufacture unique materials: microgravity alloys and crystals impossible to produce terrestrially.
• Build with local resources: lunar and Martian habitats fabricated from regolith and native metals.
• De-risk deep space: vehicles assembled and inspected in orbit before committing to a months-long transit.

None of this happens with gear from a typical fabrication shop — even our MIG setup guide won’t help you in vacuum. But the underlying mindset does: qualify your procedure, respect your materials, and control your heat. Space welding is less a new trade than an old one tested under the harshest conditions imaginable.

How Space Welding Actually Works: Processes That Survive Vacuum

In orbit, there is no oxygen to feed a flame, no air to blow across a puddle, and no blanket of atmosphere to contain a weld. For most Earth-bound methods, that sounds like a problem. In reality, vacuum is what makes several of them viable in the first place. Strip that atmosphere away, and processes that rely on shielding gas fall out of contention, while beams, pressure and friction step to the front.

The shortlist of candidates that have been flight-tested, lab-proven, or seriously proposed for orbit and beyond comes down to six: electron beam welding, laser beam welding, friction stir welding, resistance welding, brazing and soldering, and cold welding. Each handles the void in its own way.

Electron Beam Welding: The Process That Was Born for Vacuum

Electron beam (EB) welding fires a focused stream of high-velocity electrons at a joint. When those electrons collide with the metal, their kinetic energy converts to heat and melts a narrow, deep pool. On Earth, the beam would scatter against air molecules, so it must be fired inside a hard vacuum chamber. In space, that chamber is already there.

It is little wonder this was the method Valery Kubasov used aboard Soyuz-6 in 1969, a feat that ESA’s specialists later replicated and compared to a space-made weld examined back on Earth. For high-integrity structural and pressure-vessel joints, EB remains one of the most capable options.

• Pros: No shielding gas, deep penetration, small heat-affected zone, works on reactive metals.
• Cons: Heavy equipment, high power draw, sensitive to joint fit-up and beam containment.

Laser Beam Welding: The Favourite for In-Space Manufacturing

Unlike electrons, light does not need a vacuum to travel, so laser welding can function in space without an evacuated gun chamber. NASA has pursued a multi-year laser beam welding collaboration with Ohio State University to qualify the process for in-space manufacturing and thermal vacuum conditions, with a focus on off-Earth structures. Its precision makes it well suited to robotic fabrication, especially for thin-walled hardware.

Lasers still have their hurdles: they reflect badly off shiny aluminium and copper, demand tight joint gaps and draw significant power. For anyone who has fine-tuned heat input when working with thin sheet with a TIG rig, the margins will feel familiar. In orbit, though, there is no air to carry heat away, so every joule stays in the panel.

Friction Stir Welding: The No-Melt Answer

Friction stir welding (FSW) never reaches the melting point. A hardened, rotating tool is forced into the joint, and friction plus mechanical stirring plasticises the metal. As it travels, pressure fuses the softened material together. With no arc, no fume and no free-floating molten pool, it is well suited to microgravity.

NASA’s literature on welding in space and related technologies highlights FSW as a strong candidate for large aluminium structures. Its main trade-off is force: fixtures must resist considerable push, and it struggles with very thin material or complex geometries.

Resistance Welding: Spot Welds, Scaled for Space

Resistance welding generates heat from the electrical resistance of stacked sheets as a heavy current passes through them. The same physics applies in orbit as it does in a factory, which is why the principles behind how a spot welder actually works translate almost directly. It is fast, repeatable, needs no filler or gas, and pairs naturally with robotic end effectors. Limitations are mostly practical: fixed joint geometry, high current demands and awkward electrode wear.

Brazing and Soldering: Low-Heat Joining for Delicate Hardware

Brazing uses capillary action to draw filler metal into a joint below the base metal’s melting point. In vacuum, wetting improves and oxides are less likely to form, making it ideal for tubing, heat exchangers and small assemblies where fusion would cause distortion. Even self-powered reactions, such as those seen in thermite rail welding, continue to resurface in lunar construction studies.

Cold Welding: No Heat at All

When two clean, oxide-free surfaces of the same metal touch under vacuum, they can bond through metallic adhesion with no heat applied at all. It is a genuine industrial phenomenon, and in orbit it is treated as both a hazard and, increasingly, a repair tool.

Quick Comparison of Space-Suitable Processes

Across all six, the takeaway is consistent. Remove the atmosphere, account for microgravity, and the processes that survive are the ones that do not rely on convective shielding. Beams, pressure and friction are what will hold structures together off-world.

The Physics Problem: What Microgravity and Vacuum Do to a Weld Pool

On Earth, a weld pool is a well-behaved system. The arc dumps heat in, the surrounding metal pulls it away, gravity decides where the molten metal sags, and shielding gas keeps oxygen out. Every cue you read as a welder, from puddle color to the way a pool hangs overhead, is governed by gravity and atmosphere. Remove both and the puddle stops behaving like a puddle. It becomes a physics experiment you cannot fully predict.

Heat Nowhere to Go but Out

In vacuum there is no air to convect heat away, so energy leaves the weld almost entirely by radiation. Radiation scales steeply with temperature, so hot zones cool fast while adjacent metal stays much cooler. The result is a steep thermal gradient across a very short distance: an intensely hot fusion zone surrounded by comparatively cool metal.

Those gradients change cooling rates, and cooling rates change microstructure. Grain size, phase balance, and residual stress will not simply match a sea-level weld. NASA’s review literature makes the same point from another angle: heat input, fusion-zone shape, and mechanical properties must be re-established empirically rather than borrowed from ground-based procedure books (NASA Technical Report, A Review of Welding in Space and Related Technologies).

No Buoyancy, So Surface Tension Runs the Show

On Earth, hot metal is lighter than cold metal, so it rises. That buoyancy-driven circulation shapes the pool and is why out-of-position work is such a physical skill, as anyone who has fought a overhead stick welding bead knows. In microgravity buoyancy vanishes and the dominant driver becomes surface tension, which varies with temperature. The hotter center of the pool pulls liquid toward the cooler edges, driving a flow pattern called Marangoni convection.

Picture oil spreading across a warm plate: fluid moves because surface tension differs from spot to spot, not because anything is sinking. Pools in orbit behave the same way. They can be wider, shallower, or differently shaped than a gravity-shaped pool, and the flow direction flips when alloying elements change the metal’s surface-tension temperature coefficient. Predictability, not difficulty, is the real problem.

Bubbles That Never Rise, and Spatter That Never Falls

The porosity problem in one sentence: without gravity, buoyancy cannot lift gas bubbles out of a molten weld pool, so any gas that comes out of solution stays trapped exactly where it formed. On Earth a bubble floats up and escapes; in orbit it does not. The same defect that ruins a flux-cored weld on the shop floor gets harder to prevent rather than easier when nothing helps it rise.

Spatter works in reverse. Molten droplets detached by arc forces do not fall to the floor; they drift. A globule of molten steel can wander toward a window, a sensor, or a crew member’s visor. Ground crews train for spatter control for the same reason, with gravity reliably on their side.

Arc Physics in Low Pressure

An arc burning in low pressure or hard vacuum is a different animal. It constricts, brightens, and typically needs higher arc voltage for the same current, so more energy lands on a smaller area. Stability suffers too: the arc can wander, and the plasma column emits far more intense ultraviolet radiation, plus soft X-rays under some vacuum arc conditions. That is why shielding decisions in space welding stay conservative. The shielding fundamentals are covered in Welding PPE: The Complete Guide to Protective Gear Every Welder Needs, and the same caution underpins MIG welding safety precautions.

Metals Boil at Lower Temperatures

Lower pressure means a lower boiling point. In vacuum, volatile elements such as zinc and magnesium vaporize readily, well below sea-level expectations. Weld galvanized or high-magnesium alloys in vacuum and you get heavy fuming, possible porosity from condensing vapor, and a weld composition that no longer matches the base metal. Even aluminium and copper lose trace elements if heat input is not tightly controlled.

None of this makes welding in space impossible. It means ground-honed instinct must be replaced by procedure, measurement, and closed-loop control.

Safety and the Human Factor: Welding Next to a Space Station

On Earth, welding safety is a well-worn playbook: ventilation hoods, fire extinguishers, a fume extractor, and a pair of boots you can kick off if sparks find your ankle. Now picture doing that job inside a $100 billion laboratory orbiting 400 kilometers above Earth, bolted to a hundred tons of pressurized hardware, where there is no fire department, no ambulance, and no way to simply open a window. That is the reality behind space welding safety, and it is why NASA’s own literature on the subject spends as much time on protecting the station as it does on protecting the weld.

NASA’s review of welding in space and related technologies explicitly discusses the safety measures needed to protect the orbiting International Space Station and its crew during welding operations. Every hot-work task on orbit is treated like an emergency-room triage decision: what can go wrong, how fast, and what contains it.

Fire in a Can: Why Cabin Atmosphere Changes Everything

The most primal risk is fire. Human spacecraft cabins typically run at reduced total pressure with an oxygen-enriched mix compared to Earth’s atmosphere. NASA has decades of flammability research showing that materials burn very differently in these cabin atmospheres: ignition is easier, flames spread faster, and materials that would self-extinguish on the ground keep burning in orbit.

The starkest reminder is Apollo 1. During a ground test in 1967, a cabin fire in a pure-oxygen atmosphere killed astronauts Gus Grissom, Ed White, and Roger Chaffee, transforming NASA’s approach to materials flammability and leading to theflammability testing standards that still govern spacecraft hardware today. That history is exactly why nobody casually strikes an arc inside a crewed module. Any welding process is, by definition, an open ignition source hotter than anything a spacecraft designer ever wanted aboard.

Even on the ground, MIG welding safety precautions center on sparks, UV flash, and fire watch. Multiply those concerns by the fact that in space there is no fire department en route.

No Place to Vent the Fumes

Here is a problem Earth welders never face: in a pressurized spacecraft module, welding fumes cannot be exhausted outside. Open a hatch and the atmosphere leaves with the fume. That means all metal vapors, ozone, and particulates generated by a weld stay in the cabin and must be scrubbed through the station’s closed-loop life-support and filtration system. Add microgravity, and those fine particles do not drift down to a floor; they hang in the breathing zone and settle on optical surfaces, electronics, and crew mucous membranes. Contamination control becomes respiratory protection.

This is one strong argument for doing any actual fusion welding outside the pressure shell, in vacuum, where vapors disperse harmlessly. But that shifts the hazard to the person or machine doing the work.

Spatter, Bright Arcs, and Delicate Hardware

Modern spacecraft are covered in fragile, mission-critical surfaces: multilayer insulation blankets, optical windows, star trackers, antennas, and solar array joints. Molten spatter or a drifting droplet can scar a window, blind a sensor, or puncture a thermal blanket. Ultraviolet output from an unshielded arc in vacuum is intense and unattenuated, and arc processes can even emit soft X-rays. Eye protection, then, is not a nice-to-have; it is a hardware-protection and crew-safety requirement, echoing the same logic behind everyday welding PPE choices on the ground.

The Safer Welder Has Six Axes and a Camera

The dominant safety strategy in space welding research is simple: keep humans away from the arc. Autonomous and teleoperated robotic welding arms let engineers on the ground plan a weld, stream camera and sensor data, and execute or supervise the join from Mission Control. A robot does not need oxygen, does not flinch at UV flash, and cannot lose fine motor control from suit pressure. Programs like ESA’s autonomous in-orbit welding work, covered earlier in this guide, are fundamentally safety programs as much as manufacturing ones.

The human still matters enormously, though, just in a different role: reviewing procedures, watching data, and making go/no-go calls. Ground-based crews use the same discipline a pipe crew applies when validating pipe welding procedures, except their “weld inspector” is on a 400-kilometer phone line with a 200-millisecond delay.

So no, you will not see an astronaut crouched in a cabin MIG-welding a bracket with sparks bouncing off the walls. Space welding safety demands that the hot, bright, fume-generating part of the job happens in vacuum, under a robot, with humans safely on the other side of the hull.

Cold Welding: The Accidental Hazard and the Repair Opportunity

Put two polished pieces of copper in a vacuum chamber, press them together firmly, and pull them apart. On Earth, nothing much happens. Do the same thing in space and the two pieces may never separate: they have joined into a single solid without a flame, an arc, or a single degree of added heat. This is cold welding, one of the strangest and most misunderstood phenomena in space fabrication.

Despite the name, it is not welding as a shop fabricator would recognize it. There is no melt pool, no filler rod, no shielding gas, and no power source. There is only direct metallic contact: atoms on one surface getting close enough to atoms on the other that their electron clouds merge and the boundary between them simply disappears.

Why the Oxide Layer Is the Thin Shield You Never Thank

On Earth, cold welding almost never happens by accident, and the reason is a layer of chemistry we routinely treat as a nuisance: oxide. Nearly every engineering metal carries a skin of oxide only a few nanometers thick the moment it meets air. Iron rusts, aluminum oxidizes, copper tarnishes. That skin stops atoms on the two surfaces from ever touching directly, so the pieces stay separate no matter how hard you squeeze them.

In vacuum, no new oxide forms. If a surface is cleaned before launch or freshly abraded in orbit, and the protective skin is then broken by pressure or scraping, bare metal meets bare metal. At that point, metallic bonding takes over across the interface and the joint forms spontaneously at room temperature.

Which metals are vulnerable? The ones whose oxide layers are soft, brittle, or easily ruptured: aluminum, copper, and gold are the classic examples, and they are all over spacecraft structures and electrical hardware. Metals with tough, self-healing, persistent oxide layers — stainless steel, titanium, chromium-rich alloys — are far more resistant. That is exactly why spacecraft designers use them deliberately in mechanisms that must never seize. Incidentally, the same contact-pressure physics is what governs spot welding copper on the shop floor, just with current added and no vacuum in sight.

What Engineers Fear: Seized Bearings and Stuck Docking Rings

The hazard side of cold welding shows up anywhere two identical, unlubricated metals repeatedly touch in vacuum:

• Antenna gimbals and deployment hinges that must swing open years after launch
• Solar array joints and drive mechanisms that rotate thousands of times
• Bearing races, latches, and release devices on payload doors
• Docking interfaces, where two vehicles press metal against metal during capture
• Electrical connectors that must still disconnect during an emergency separation

When these parts gall and seize, the result is not a cosmetic defect. It is a mission-ending failure that cannot be fixed by radio command from the ground. Engineers counter it with dissimilar metal pairings, solid-film lubricants such as molybdenum disulfide, anodized or plated surfaces, and coatings that survive where oil and grease would boil away. The underlying principle is simple: never let two clean, compatible metals rub in vacuum.

Turning the Hazard Into a Repair Tool

Here is where the story flips. The same effect that can ruin a hinge can also seal a puncture. If a bare aluminum patch pressed against an aluminum hull fuses on contact, then a small, hand-held device could patch a micrometeoroid hole without heat, power, shielding gas, or a welder in a pressurized suit.

That idea is exactly what the ASTROBEAT investigation is testing. Launched aboard SpaceX CRS-31 in November 2024 and sponsored by the ISS National Laboratory, the project applies metal patches to simulated spacecraft hulls in orbit to evaluate whether cold welding can serve as a rapid, on-the-spot repair method for future missions (ISS National Lab mission overview). A parallel announcement described the work as “space, the final frontier for welding,” framing cold welding as a candidate technology for keeping spacecraft flying rather than scrapping them (press release). NASA Technical Reports Service literature on welding in space notes cold welding among the processes that behave fundamentally differently off-world (NASA NTRS, 2023).

Cold Welding Already Works on Earth

Cold pressure welding is a mature industrial process, not a space curiosity. Factories routinely join non-ferrous wire — copper and aluminum especially — by stripping or scratching away the oxide and pressing the ends together under high force. It is fast, needs no filler, produces no fume, and makes a joint that conducts electricity as well as the parent metal. If you have ever wondered how a spot welder works at a mechanical level, contact pressure underpins the whole process. Operators still work under ordinary shop safety rules, and hand and eye protection remains standard — our welding PPE guide covers the gear that keeps shop workers safe around press equipment and adjacent welding stations.

So cold welding is simultaneously a design defect and a repair strategy. Avoid it in every mechanism that must move, and you may someday rely on it to save a spacecraft hit by debris. That duality is what makes it the most fascinating subplot in space welding.

Real Programs and Research: NASA, ESA, Universities, and Industry

Space welding isn’t just a headline topic. It’s an active research field with named programs, funded experiments, and published papers you can read for free. If you want to go deeper than the history lessons, these are the people and projects shaping where the technology goes next.

The NASA Technical Reports That Anchor the Field

Two documents from NASA’s Technical Reports Service (NTRS) are the best starting points for anyone serious about this subject. The first is “A Review of Welding in Space and Related Technologies”, published by R. Naden in 2020. It surveys the processes that have been tried or proposed, the physics that changes in vacuum, and the open engineering questions. The second is Sowards’ 2023 paper, “Welding in Space: Past, Present, and Future”, which frames the timeline from Soyuz-6 forward and identifies where development effort is actually needed.

Both live on the NTRS public database, and both are free to download. Together they function as the field’s orientation documents: one sets up the technical landscape, the other charts the trajectory.

One Research Gap: Knockdown Factors

Among the most important takeaways from NASA’s review work is a plain admission about data. Engineers designing terrestrial welded structures rely on established knockdown factors: conservative reductions applied to a material’s allowable strength to account for weld variability, residual stress, and inspection uncertainty. For orbital structures, those factors are essentially borrowed from Earth-based testing rather than derived from actual space welding data. NASA research notes that on-orbit welding experiments are needed to derive knockdown factors properly for welded joint design in space.

ESA: Scrutinising an Actual Space-Made Weld

ESA took a hands-on approach to validating the science. Engineers examined a weld produced in orbit inside ESA laboratories, then used electron beam welding to reproduce the original 1969 Soyuz-6 method on the ground. Comparing the two let them separate the effects of the space environment from the effects of the process itself, which is exactly the kind of controlled comparison the field has been missing for decades.

Ohio State, the NSF, and Laser Welding in Thermal Vacuum

On the American university side, a NASA–Ohio State University collaboration has focused on laser beam welding for in-space manufacturing, running tests under thermal vacuum and simulated microgravity conditions. Complementary NSF-funded abstracts on laser beam welding in thermal vacuum have expanded the parameter window researchers can draw on. Laser welding is attractive for space because the energy source is precisely steerable and needs no consumable filler gas, making it a natural fit for robotic systems.

Academic discussion has also moved into conference proceedings. Embry-Riddle’s Space Congress published a paper titled “Space Welding: On the Agenda”, arguing that joining technology deserves formal attention in mission planning rather than being treated as an afterthought.

Paton Institute and the ISS National Lab

The E.O. Paton Electric Welding Institute in Kyiv has led this field since the beginning, and it continues publishing through The Paton Welding Journal, covering everything from electron beam processes to welding robotics for extreme environments.

Meanwhile, the ISS National Laboratory has sponsored commercial research on cold welding techniques for spacecraft repair, flown aboard SpaceX missions with industry partners. This is where government science meets commercial application, and it’s producing data on joining metals without heat at all. For background on how resistance-based joining works before you compare it to vacuum processes, see How Does a Spot Welder Work?

Note: Nearly all of these reports are openly accessible. Search NTRS for the Naden and Sowards papers, check ESA’s media library for the weld examination story, and browse Embry-Riddle’s institutional commons for the Space Congress proceedings. No paywall, no subscription.

What these programs share is discipline: qualified procedures, documented parameters, and post-weld inspection treated as non-negotiable. That same procedural rigor is exactly what separates professional work on the ground, as covered in Pipe Welding Procedures.

Common Mistakes, Myths, and Misconceptions About Welding in Space

For most welders, the idea of striking an arc in orbit sounds impossible. That skepticism has fueled a long list of myths that often overshadow the reality of the process. While welding has been demonstrated in space, the environment creates challenges that are often misunderstood. Here’s a breakdown of the most common misconceptions, paired with the facts behind them.

Myth 1: “You Can’t Weld in Space”

This is one of the easiest claims to disprove. During the Soyuz-6 mission in 1969, cosmonauts Valery Kubasov and Georgy Shonin successfully performed electron beam welding, brazing, and cutting inside the unpressurized service module chamber. The resulting joints were sectioned and tested, confirming their integrity. Since then, these results have been studied and replicated, with the electron beam method used for these historic welds being analyzed by ESA in its own laboratories. In fact, the vacuum of space is ideal for electron beam welding, as it removes the need for an evacuation chamber entirely.

Myth 2: “Vacuum Makes Welding Easier Because There’s No Shielding Gas”

While it’s true that no argon or CO₂ is needed to protect against atmospheric oxygen, the vacuum creates its own set of hurdles. The arc column constricts, arc voltage rises, and strike-up becomes far less predictable. Most notably, the arc emits much more intense ultraviolet radiation than its Earth-side counterpart. On top of this, contamination control becomes stricter, as any oils or outgassing materials are exposed directly to the weld pool. As detailed in NASA’s “A Review of Welding in Space and Related Technologies”, these changes drastically alter the process. These intensified hazards alone are reason enough to re-evaluate welding PPE choices for any orbital application.

Myth 3: “Everything Cold-Welds Instantly in Space”

Despite its popularity, this myth is heavily exaggerated. Cold welding only occurs when two chemically compatible metals are perfectly clean and oxide-free. On Earth, native oxide layers form within nanoseconds, preventing this from happening to everyday hardware. Anodized aluminum, oxidized steel, or coated titanium components will not spontaneously fuse in orbit. The real concern lies in moving parts, such as bearings, hinges, docking interfaces, and solar array joints. When coatings wear away through friction, virgin metal can be exposed, creating the small, genuine risk of cold welding in tribological contacts.

Myth 4: “Zero Gravity Gives You a Perfect Weld Pool”

Microgravity actually removes the stabilizing forces that welders rely on. On Earth, gravity drives convection and causes spatter to fall away. In space, surface tension and Marangoni flow dominate, causing the molten pool to ball up and behave unpredictably. Gas bubbles have no buoyancy to escape, and molten droplets don’t fall, but instead drift throughout the surrounding area. These factors make puddle control a completely different skillset from its terrestrial counterpart.

Myth 5: “We’ll Just Send a Welder to the Moon”

The iconic image of a suited welder striking an arc is far from realistic. Spacesuits limit dexterity, vision, and mobility, while life support severely restricts time and consumables. The true milestones lie in autonomy and robotics, from ESA’s analysis of the first autonomous weld performed in orbit to cold-welding patch demonstrations flown to the ISS National Lab. Moving forward, humans will be programmers, supervisors, and inspectors, with robotic arms performing the majority of arc time.

The Earth-Side Habits That Don’t Translate

Many failures don’t stem from myths, but from applying shop habits directly to orbit. The most common oversights found in design reviews include:

• Unaltered procedures: Cooling in vacuum is almost entirely radiative, not convective. A procedure qualified in atmosphere will not yield the same microstructure in orbit.
• Ignoring knockdown factors: Limited inspectability means orbital welds must be designed with reduced allowable strengths. Treating them like shop welds greatly underestimates risk.
• Blindly relying on terrestrial codes: While foundational, standards like AWS D1.1 and ASME Section IX don’t automatically qualify orbital procedures. The structured discipline found in pipe welding procedure guides serves as a starting point, not a guarantee.
• Underestimating distortion: Steep thermal gradients can lead to residual stress and defects, such as undercut, that must be accounted for prior to flight.

The Future of Space Welding: Autonomous Robots, Lunar Factories, and What It Means for Welders on Earth

Fifty-six years ago, one small switch in an unpressurized Soviet capsule sparked the beginning of off-world joining. Now, as humanity sets its sights on permanent settlements beyond Earth, that same feat is evolving into an entirely new industrial frontier. The future of space welding will not rely on a suited welder floating in the void, but on smart robotics, lunar construction, and the skills that today’s fabricators are already developing here on Earth.

Autonomous Robots Leading the Charge

The single greatest shift coming to this field is autonomy. With the extreme hazards of space, robotic and autonomous systems greatly reduce the need for risky extravehicular human welding on spacecraft exteriors. This isn’t a concept for the distant future either, as ESA has announced the analysis of the first-ever autonomous weld performed in orbit, using robotic arms and high-precision tools. These breakthroughs are paving the way for self-sufficient repair fleets that can mend hull breaches or reinforce trusses without endangering a crew.

To support this level of precision, the next wave of orbital welders will utilize AI-guided inspection and closed-loop weld control. These systems will be able to detect defects in real-time and adjust parameters mid-pass, something that is crucial in an environment where a single error could mean mission failure. Much of this data is being built upon decades of research, with NASA’s ongoing work highlighted in technical reports such as “Welding in Space: Past, Present, and Future” and “A Review of Welding in Space and Related Technologies”.

Lunar Factories and the Infrastructure of Tomorrow

While orbit will be the testing ground, the true payoff lies on the surface of other worlds. For large-structure assembly in LEO, modular trusses and antennas too massive to launch whole will be joined in space to support lunar and Mars missions. From there, the focus shifts to lunar surface welding and ISRU-built habitats, where regolith-derived metals will be used to construct everything from radiation shields to pressurized modules.

This off-world building boom is also fueling a demand for microgravity manufacturing of specialty alloys and fibers, which is a recognized commercial driver of the expanding in-space economy. As private industry continues to invest, groups such as the ISS National Lab are testing revolutionary processes like cold welding for repairs. This commercial demand is only projected to grow, opening the door for more frequent orbital fabrication runs that will perfect these procedures for deep space operations.

What This Means for Welders on Earth

The technologies being forged for the vacuum of space will have a massive impact back home, and skilled tradespeople are more vital than ever. Today’s welders and fabrication engineers can gain an edge by mastering the same pillars being researched for off-world use:

• Vacuum procedure discipline: The meticulous control needed in orbit reinforces the importance of proper parameters, similar to dialing in your machine through guides like How to Set Up a MIG Welder.
• Procedure qualification: Just as space joints require validation, terrestrial codes demand strict WPS/PQR adherence, a practice that translates across all industries.
• Metallurgy fundamentals: Understanding how heat transfer and microstructures change in extreme environments strengthens your knowledge for exotic alloys and critical repairs.
• Robotic welding skills: With automation at the forefront, familiarity with mechanized processes is becoming non-negotiable for the next generation of welders.

From mastering the basics of Welding PPE to perfecting advanced processes, these foundational skills are the very same ones that will build humanity’s first extraterrestrial shipyards.

Actionable Takeaways and the Return to 1969

As we look towards the horizon, there are a few key takeaways to carry with us. First, the notion that welding is bound to Earth has been disproven for over half a century. Second, the future lies in autonomous, data-driven joining rather than manual EVAs. Lastly, the growing in-space economy will create a demand for tradespeople who understand both the art of welding, and the science behind it.

So, as we envision robotic arms fusing beams on the Moon, we must circle back to that fateful moment on October 16, 1969. When cosmonaut Valery Kubasov flipped that switch in the vacuum of space, he didn’t just join two metals together. He sparked a dream that, through innovation and the relentless skill of fabricators, is finally ready to help build our home amongst the stars.

Frequently Asked Questions

Has anyone actually welded in space?

Yes. On 16 October 1969, Soviet cosmonaut Valery Kubasov used the automated Vulkan unit aboard Soyuz-6 to perform electron beam welding, brazing, and cutting in open space. Since then, NASA, ESA, and the Paton Institute have conducted further orbital and ground-analog welding experiments.

Can you weld without oxygen or shielding gas?

Yes. Space is already a vacuum, so shielding gas is unnecessary — the atmosphere that shielding gas protects against simply isn’t there. Processes like electron beam welding actually require a vacuum, which is why they translate so well to space.

Why is welding in space so difficult?

Heat can only leave the weld pool by radiation instead of convection, gravity can’t float gas bubbles out of the molten metal, surface tension dominates pool shape, and vacuum lowers boiling points so metals vaporize more easily. Arc behavior also changes at low pressure, making procedures difficult to transfer from Earth.

What is cold welding and why does it matter in space?

Cold welding is solid-state bonding between clean, oxide-free metal surfaces in direct contact — no heat needed. In space it’s both a hazard (seized bearings, hinges, and mechanisms) and an opportunity, since it could let astronauts patch spacecraft hulls with metal patches without a heat source.

What welding processes are best suited for space?

Electron beam welding has the longest flight heritage, laser beam welding is being developed with NASA and Ohio State University for in-space manufacturing, and friction stir welding is attractive because it is solid-state — no arc, no fume, and no molten pool to escape in microgravity.

Is welding in space dangerous for astronauts?

It can be. Arcs in low pressure emit intense ultraviolet radiation, spatter can damage sensitive equipment, and welding fumes have nowhere to go inside a closed cabin. That’s why most current concepts favor robotic or autonomous welding systems over a human with a stinger.

Will we weld on the Moon or Mars?

Very likely eventually. Building habitats, landing pads, and infrastructure from local materials reduces the astronomical cost of launching mass from Earth. Lunar vacuum is actually favorable to electron beam welding, though power, dust, thermal extremes, and autonomy remain big hurdles.

Do Earth welding codes like AWS or ASME apply to space welds?

Not directly. AWS D1.1, ASME Section IX, and similar codes were written for terrestrial conditions. NASA researchers have noted that on-orbit welding experiments are still needed to derive knockdown factors for welded joint design in space structures.