Space-made weld scrutinised in ESA lab

The Agency’s Materials and Electrical Components Laboratory centre in Netherlands hosts a portfolio of facilities being applied to compare this historic space-made weld against, identical samples produced back on Earth.

ESA Materials Engineer João Gandra comments: “If human space exploration is going to become truly sustainable and self-supporting, then in-space manufacturing will become commonplace, with the ability to weld being an important element of that vision. So we need to check how easy it is to weld in space.

“So what we are doing with this experiment is to investigate what is different about materials being joined in orbit. The weightlessness prevailing in space means we aren’t working with the same gravity-driven physics we normally take for granted.

“For instance while convection currents influence the way a molten metal ‘weld pool’ forms, cools and solidifies on Earth, in microgravity molten metals behave more like liquid blobs, shaped by surface tension instead. Then there are other complex variables such as space radiation and external vacuum to consider.

“Right now we don’t really understand how these factors might interact, and the consequences they might have on the resulting material properties for any product. We can run computer simulations, but what we lack normally is any sort of empirical data to calibrate and improve our predictions. Which is why this spot weld is so valuable to us.”

Welding – the heat-based joining together of metal parts – is fundamental to human civilisation, at least down on the ground. The same will doubtless be true for any future in-space economy. It might seem surprising then that the 450 tonne International Space Station was pre-fabricated on Earth and then bolted together in space without a single weld being performed while in orbit. 

In fact, welds have only ever taken place in orbit experimentally; the first occurred on the USSR’s Soyuz-6 spacecraft in October 1969, then aboard the US Skylab and Soviet Salyut-7 space stations in 1973 and 1984 respectively. But in the 1990s, US-Russian plans to develop a multi‑purpose welding tool for maintenance on the International Space Station were abandoned due to safety concerns and logistical difficulties.

This means no welds have been performed in orbit for four decades – until this recent automated experiment, involving an electron beam welding gun, flown on a SpaceX Falcon 9 launched from Cape Canaveral on 6 May.

This experiment employed electron beam welding, the very same method used during the 1969 Soyuz-6 experiment. It involves directing a beam of high-velocity electrons onto the metal, so that kinetic energy is transformed into heat. Electron beam welding has the advantage of being highly controllable, penetrating deep into the metal to be welded, with no wasted energy. It can only be performed in high-quality vacuum, making electron beam welding a good fit for space. And this system may be capable not just of welding, but also cutting and 3D printing.

The entire welding experiment took place within a cylinder about the size of an office water dispenser, comprising a carrousel of multiple sets of relevant aerospace aluminium alloys, plus a second unit filled with batteries for powering the system plus avionics for remote operation and data transmission.

The experiment was initiated by US startup ThinkOrbital and incorporated a welding gun pioneered by the UK’s The Welding Institute, TWI.

“It’s an honor to work with ESA and NASA on this groundbreaking technology,” comments ThinkOrbital CEO and co-founder Colonel Lee Rosen (USAF, retired).“This technology is critical to humanity’s future in space. Not only are we demonstrating ThinkOrbital’s technology for in-space construction, we’re also contributing to ESA’s important scientific research and understanding of revolutionary technologies that will improve our collective ability to work and live in space.”

João adds: “ESA was invited to participate in the experiment, providing expert knowledge on material testing, as well as technology development and maturation.” Samples welded while flying in space have been returned to Earth for analysis by both ESA and NASA.

“We hope to be involved in further test flights, targeting progressively more ambitious welding operations,” João concludes. “This campaign is extremely well aligned with ESA’s strategy to develop in‑space manufacturing and servicing. It is a key enabler for the new space economy and provides another tool in humanity’s toolbox as we ventures towards deeper and longer space exploration missions.”