José Manuel Torralba, IMDEA MATERIALS

The first “part” ever printed in space was a very thin rod shaped like an “S”. The “S” is a simple shape, but it poses some difficulty because it involves two changes in curvature. We could almost say it was a 2D print.

But months later, a revolutionary achievement took place aboard the International Space Station (ISS). In ESA’s Columbus laboratory module, tensile test specimens were printed which, this time, were three-dimensional parts. This milestone marked the completion of the start-up phase of the first metal 3D printer in Earth orbit.

Astronauts can now print metals in space, and this will change many things for future space missions. To begin with, it supports the idea of establishing a base on the Moon.

Home Printing

In recent years, 3D printing has become hugely popular. Today, it’s easy to get hold of a plastic printer, and many children even ask for one as a Christmas present so they can manufacture at home whatever their imagination comes up with.

With free design software, they can draw any kind of part or figure and then turn it into reality with a home printer. This democratisation of 3D printing gives the impression that it is a simple technology and that it is easy to manufacture anything.

The reality, however, is much more complex when moving from plastics to composite materials, and even more so when it comes to metals.

The Challenge of Printing Metals

Metal 3D printing requires controlling dozens of additional variables: from laser power to material density, as well as the printing atmosphere and deposition speed, each parameter directly influences the quality of the final part.

On top of this, the required equipment is large and must operate at extremely high temperatures, sometimes above 1,600 °C, depending on the alloy. Adapting this technology for space, in reduced dimensions and microgravity conditions, has been one of the greatest challenges to overcome.

The “Lack” of Space

There are various methods for metal 3D printing, most based on metallic powders.

However, for printing metals in space, the chosen approach has been Directed Energy Deposition (DED), using metal wires instead of powders. This method derives from laser cladding, traditionally used for metallic coatings and the repair of surface defects in industrial parts.

With DED, a metal wire is deposited layer by layer while a high-energy laser locally melts the material, achieving full densification of the part.

Metal wires are less hazardous to handle in space than powders, but they still require large equipment and the use of a laser to melt the material.

The advent of computer-aided part design and industrial robotics enabled this technology to evolve from laser cladding to DED, making it possible to manufacture large three-dimensional components. Possibly the largest part ever produced this way is a 4.5-ton stainless steel bridge that was installed for a time as a demonstrator over one of Amsterdam’s canals.

Melting metal wires with a laser beam is no trivial matter due to the huge number of variables that must be controlled (many linked to the material being printed, others to the laser’s type and power, others to printing parameters, etc.). There are so many that even on Earth the process is complex. Doing it in microgravity conditions, and with a compact printer small enough to fit into a spacecraft, makes things far more difficult.

The Size of a Microwave

The first challenge was to develop a printer that could be installed on the ISS while taking up no more room than a washing machine. In the end, the consortium behind the project managed to build a printer weighing “only” 180 kg and measuring 80 × 70 × 40 cm, roughly the size of a microwave. No information is available about the laser’s power, but melting stainless steel requires lasers of over 500 W.

The process was carried out in a nitrogen atmosphere, with oxygen thoroughly evacuated from the printing chamber.

The printer was installed during a mission in January 2024, but it wasn’t until June that a curved line in the shape of an “S” was successfully printed. With that “S”, the possibility of at least 2D printing was validated. The next step was to prove that it was possible to move from 2D to 3D, and that happened in August, when the first three-dimensional sample was obtained. By the end of 2024, the final parts had been produced.

The aim was to demonstrate that it is possible to manufacture metal parts in microgravity. The next step is to characterise the microstructure formed and the mechanical properties of the parts printed in orbit, and compare them with identical reference batches printed on Earth. This will make it possible to study the effects of microgravity on porosity, solidification, anisotropies (physical or other characteristics that vary depending on the direction in which they are measured), and mechanical properties.

The printed parts have already returned to Earth for testing. So far, we don’t know the results, but we expect them to be published soon in a leading scientific journal.

Metal Manufacturing in Orbit: A Key to Space Exploration

Printing metals in space is a major step forward towards self-sufficiency in space missions, especially for long-duration explorations such as those planned for the Moon or Mars.

The ability to print components on-site reduces reliance on costly shipments from Earth and enables immediate repairs and rapid adaptations to unforeseen needs during space missions.

Until now, the breakage of a metallic component in space has been a very serious problem: it is estimated that the urgent delivery of a replacement to the space station would take about a year.

Moreover, metal manufacturing in microgravity drives technological innovation and paves the way for longer, more autonomous missions.

Going Further

The capacity to produce parts directly in space is essential for deep space exploration, as it ensures that critical equipment can remain operational without having to wait for resupply, making human spaceflight more viable and sustainable.

This advance also contributes to building a circular economy in space, allowing for the recycling of materials and the manufacturing of new tools from existing resources.

A small step for technology, but a giant leap for space exploration.

José Manuel Torralba, Full Professor at the Carlos III University of Madrid, IMDEA MATERIALS

This article was originally published in The Conversation. Lea el original (content in Spanish).