Welding in space is a compelling prospect, and I recently discovered that NASA plans to launch its moon-orbiting station Gateway in 2024. So, I decided to dig deeper and find out if space welding is plausible or not.
Welding in space is possible and highly practical through processes like laser and electron-beam welding, though there are certain safety challenges. Several independent companies like Busek and Made in Space are already developing robotics to make space welding feasible.
Currently, any damage sustained by the International Space Station has to be repaired by welding and launching parts from Earth, which is an expensive and inefficient process. So, how do we get around it? By welding structures in space, of course.
In this blog post, we will explore the process of welding in outer space and discuss some of the challenges faced when performing this type of welding. Stay tuned – we will also be discussing the benefits of welding in outer space.
The challenges of welding in space
Welding in outer space may sound like something out of a science fiction movie, but is it really possible? The answer is yes – welding in outer space is possible and has been done by astronauts on the International Space Station.
Welding is one of the most critical skills for a space mission. It is used for everything from repairing broken equipment to building new structures. But welding in space is not easy. There are many challenges that astronauts must overcome to weld in space.
Metal solidifies differently in microgravity.
On Earth, the gravity we experience is equal to 1 g. In space, astronauts operate in 0 g or microgravity environments. In 1 g, the molten weld pool loses its heat to the surrounding air.
This causes it to cool down and become dense. The denser portion moves to the bottom due to gravity, while the hotter part is pushed up. This creates a uniformly mixed stable weld.
However, there’s no air in space, so the molten pool loses its heat slower and doesn’t become as dense. Also, the denser part doesn’t move to the bottom without gravity.
Instead, the upper portion of the pool cools first and accumulates at the top. So, overall, the weld takes longer to cool, and its final density is inconsistent.
The vacuum of space also causes surface tension and creates ripples on the weld pool. So, space welds have fundamentally different and unpredictable properties compared to Earth welds.
In the microgravity of space, the contaminants released during the welding process tend to stay in the air, where they can interfere with the spacecraft equipment. During external welding of the spacecraft, such contaminants can accumulate on and interfere with electronics or optical surfaces.
These contaminants can also cloud astronauts’ visors and be inhaled by the astronauts, which is one of the common dangers of welding.
Molten droplets can float off in a vacuum.
The weld pool can spew molten droplets in microgravity in response to small vibrations or shocks, like an astronaut putting their hand on the weld structure. These droplets pose a significant risk to spacesuits and other space equipment.
On a related note, check out my welding safety checklist to avoid common welding hazards.
Laser beam welding challenges
Laser beam welding is a relatively new process. It’s easy to master, offers good weld control, and doesn’t require a shielding gas or a depressurized space chamber.
The drawback of laser welding in space is the shallow penetration profile and the fact that a large amount of the beam is reflected because metallic surfaces are very reflective.
The reflected laser beam can damage the spacesuit of astronauts. And if it falls on delicate parts of the spacecraft, it can easily cause unwanted damage.
Electron-beam welding challenges
Electron-beam welding (EBW) is a promising space welding process. It offers some of the best welding penetration – it can weld two inches deep into steel with a width fewer than 0.2 inches. The workpiece is insulated from the heat, and there’s minimal distortion.
However, EBW emits significant amounts of X-rays that are harmful to humans and cameras. For this reason, the power and voltage levels have to be kept very low.
For instance, in 1984, the Universal Hand Tool, made by the Ukrainian Paton Institute, only allowed cosmonauts to weld metals around 1 mm thick using electron welding.
Another problem with using EBW in space is controlling its beam, which is very narrow. And given the pressurized astronaut suits and rigid gloves, precision welding is difficult.
How some companies are overcoming the challenges of welding in space
Robot or semiautonomous welding can overcome a lot of the welding challenges in space, like dangerous exposure and maneuverability. We’ve been using robot welding for decades in the automotive industry, so it stands out as a promising technique for welding in space.
Busek’s Teleoperated Electron-Beam Welding
The current closest in-progress project to robot welding is directed by Busek Co., an independent business that’s supported by NASA.
Busek’s SOUL (Spacecraft on Umbilical Line) system consists of a less than 10 kg robotic vehicle attached to a larger parent spacecraft through an umbilical cable. The cable provides the power and commands necessary for remote operation.
SOUL was initially made for capturing space debris. By adapting the SOUL system for electron welding, NASA hopes to build a semiautonomous and teleoperated welding system.
Conceptually, SOUL can perform internal (vacuum) welding, repair debris damage, service heat shields, and inspect the external surfaces of the International Space Station (which conventionally requires manned operations).
Mobile End-effector Laser Device (MELD)
MELD by Made in Space is another in-progress work on space welding funded by the Small Business Innovative Research (SBIR) program. The system consists of a dextrous “end-effector” (the robot equivalent of a hand) attached to an autonomous robot.
The end-effector incorporates multiple tools, including avionics and cooling, vision, and laser systems. With minimal interaction, MELD can laser weld aerospace-grade metals to repair and assemble structures like pressure vessels, solar arrays, habitats, and trusses in-orbit or on the Martian or lunar surface.
The benefits of welding in space
Welding in space is a relatively new concept, but it has already shown tremendous promise. There are many reasons why welding in space could benefit both astronauts and spacecraft.
The hazards of spaceflight
Space is a harsh environment, and even slight structural damage to the Space Station can prevent it from functioning. So let’s discuss some common space hazards and see how welding could be helpful in space.
The Sun emits constant heat and radiation. As satellites orbit the Earth, their paths alternate between the Sun’s extreme heat and Earth’s cool shadow, leading to cracks over time. Besides that, the direct effects of the Sun’s radiation can make the metal brittle and more prone to cracking due to shocks.
Secondly, the solar system is brimming with rock debris and micrometeoroids. When they collide with the Space Station, they can damage critical areas like solar arrays, pipelines, and habitation modules.
Other sources of structural damage can be the vibrations caused by the docking of space shuttles or when maneuvering the Space Station. Or, if the pressurization system gets compromised, it causes decompression and stress in the spacecraft.
How space welding can help
Given the hazards of space navigation, it’s clear that welding is an essential tool for astronauts.
However, currently, the best way to repair damages is by welding replacement parts on Earth, launching them into space (which can often cost over $100 million), and having the astronauts perform rigorous repairing procedures.
Hence, NASA’s priority is to develop an in-space welding apparatus that will allow the astronauts to perform quick, independent repairs and save up on the aerospace budget.
For example, the Space Station relies on hermetic seals to pressurize the air and keep the astronauts alive. So, any fault in the seals has to be fixed, or new seals have to be welded ASAP, without waiting for equipment from Earth.
Recently, NASA has also been considering additive manufacturing technology – another term for 3D printing – of metals to manufacture and repair parts in space.
Assuming metal 3D printing is successful, on-site welding capabilities will be even more desirable as both the processes go hand-in-hand.
For instance, if a large crack develops abroad the Station, simple welding might not be sufficient. The solution would be to first 3D print a metal plate and then weld it into the crack.
Finally, long-term space projects like NASA’s proposed Lunar Gateway make space-welding a greater necessity. The farther such stations move from Earth, the greater will be the costs and risks of shipping parts from Earth.
The future of welding in space
Welding in space is a highly-anticipated technology. So, given the current scientific progress, what can we expect the future of space welding to look like?
Which welding technique is the best?
Most traditional welding techniques can be impractical and unpredictable in space. Friction stir welding, for instance, requires heavy and custom-built fixtures and leaves a hole that needs to be filled.
Any welding technique that relies on filler material like wire feed welding can cause trouble with storage and release spatter, which is dangerous in microgravity.
Plus, the quality and structure of the weld are pretty susceptible to temperature, gravity, and weld environment, all of which are abnormal in space. Currently, we need more experiments to conclude which space welding technique will be popular in the future.
So far, experiments by Ukraine’s Paton Institute and NASA have highlighted electron-beam welding (EBW) and laser welding as potential candidates.
Electron-beam welding sounds promising.
EBW only works in a vacuum environment, as otherwise, the heat from the electron beam gets dispersed into the air.
Luckily, this makes EBW a viable welding option for astronauts working in depressurized chambers.
EBW has multiple applications on Earth – it’s used to weld large structures like the blades of wind turbines as well as smaller and delicate pieces like the sensors on the drilling arm of the Mars Curiosity rover.
EBW works with most metals, including sensitive ones like aluminum and Inconel. In a single pass, it can weld 2 inches deep into steel. The penetration control is incredible; it can weld pieces as thin as 0.0001 inches. EBW can also weld different metals together.
The heat loss is less than 10%, so it’s desirable for welding near heat-sensitive zones as very little heat gets spread into the environment.
Finally, EBW doesn’t require any filler metal. This is especially important for welding in space because we want to take as little storage into space as possible.
Given the efficiency, penetration profile, and vacuum operation of EBW, it’s arguably the best choice for welding in space for companies like NASA and SpaceX.
Laser beam welding and other possibilities
Another great candidate for future in-space welding is laser welding. Its only apparent drawbacks are the shallow penetration and laser reflection from shiny surfaces.
Unlike EBW, laser welding could be used by astronauts within pressurized interiors. And shielding gases may be used to increase the penetration. However, shielding gases are expensive and would make fume extraction a significant problem.
There are probably other different welding techniques that will work in space, but there’s a notable lack of scientific research and experimentation regarding space welding.
For example, in the vacuum chambers on Earth, low-metal arc welding with a consumable electrode has proved to be stable at high pumping rates. However, it’s yet to be successfully tested in space.
Having an in-space welding apparatus can significantly reduce shipping costs and allow astronauts to deal with immediate hazards quickly. In addition, given NASA’s interest in future exploration missions and the development of metal 3D printing, welding in space is hopefully just around the corner.