Welding in space is different from welding on Earth. The Russians were the first to explore welding in zero gravity and/or in a vacuum. As reported by the Sydney Morning Herald, the Russian cosmonaut Valery Kubasov was the first person to attempt vacuum-welding in space in the 1960s, as part of the preparations to build the first world space station “Salyut 1.”
Kubasov’s experiments were a turning point for zero gravity operations. The need for effective welding techniques in weightless conditions became apparent in the 1990s, when the intricately designed International Space Station was launched. More specifically, in-space welding might encompass repairing damaged hulls from space debris punctures and re-strengthening structures that have been weakened by long periods of use.
Soviet In-Space Welding Experiments
The only real tests of in-space welding techniques using conventional approaches occurred during the Soviet tests. On Soyuz 6 flight in 1969, Kubasov used a cylinder inside the unpressurized orbital craft, called the “Vulkan furnace,” which he was able to control remotely. He tried out three different welding devices via an electron gun:
- Electron Beam Welding – This process sends electrons at a very high velocity to the specific areas of the contact surfaces of the metals for joining.
- Low-Pressure Plasma Arc Welding – The plasma arc process is constricted. It requires a water-cooled spray nozzle to restrict the arc to get the properties necessary for welding.
- Consumable Electrode Welding – This is another form of arc welding that uses a consumable electrode.
However, the Russian crew over-estimated their skills and under-estimated the risks. Due to their attempt at making welds in space, they nearly ruptured the life-sustaining capsule, which would have caused the death of all onboard. Fortunately, the cosmonauts were lucky and no lives were lost in the welding experiments.
Challenges Welding in Space
Much of NASA’s maintenance and repair work happens on the ground and not in space. NASA’s technology experts first sought to avoid any need for in-space welding. For example, they constructed space vehicles with materials that can withstand space travel, made of materials such as ceramic and aluminum.
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The reason for this approach is that in-space welding can be extremely challenging. The structure, composition, and quality of a weld depends on the distribution of temperature in the weld pool and the distribution of molten materials as the weld is formed, which is difficult to control in space. Welding techniques that rely on cautiously balanced shielding gases would also be tough to manage as gases behave differently in zero gravity and airless environments.
Another problem is securing welding power sources. Portable generators use surrounding air for cooling which is not possible in space. Since aluminum is the main metal used in space construction, TIG welding would be the go-to technique for repairing parts of a spacecraft; but, the dexterity and precision required for TIG welding would be difficult to accomplish in zero gravity. Electron beam welding demands a vacuum rather than a shielding gas to protect the weld, which cannot be easily done inside the spacecraft.
NASA’s Innovative Welding Techniques
Nowadays, NASA employs a number of innovative welding techniques that enable spacecraft to withstand the rigors of space travel while also allowing for some repairs to be conducted in space:
- Friction Stir Welding – Friction stir weldingis a technique that uses frictional heating with forging pressure to produce high-strength bonds essentially free of defects. A rotating pin tool softens, stirs, and forges a bond between two metal plates to form a welded joint. NASA has developed a brand-new design for a friction stir welding tool.
- Ultrasonic Stir Welding – Another NASA-developed weld process, ultrasonic stir welding,uses a stir rod to stir the plasticized abutting surfaces of two metallic alloy pieces to form the weld joint. Heat is generated by an induction coil. The ultrasonic energy reduces unwanted forces, increases travel rates, and lessens wear on stir rod.
- Handheld Laser – For small welding jobs, especially in tight spaces, NASA developed a handheld laser. It’s useful due to its precision, ability, and maneuverability. This tool was originally developed to repair parts of the shuttle engine, but has since been licensed by NASA to be used in many other industrial processes.
The challenges presented by the concept of welding in space and the development of the tools needed to accomplish this demanding yet necessary task have in fact greatly stimulated the advancement of welding technology.