The European Space Agency said on 1 October that the fifth sample from the Metal 3D Printer inside the ISS Columbus module had returned to Earth. It contains two small thrusters designed by the German Aerospace Center, DLR. That makes it different from the programme's earlier material samples: the next objective is not only to inspect printed metal but to test a functional geometry exposed to heat and pressure.

ESA astronaut Sophie Adenot retrieved the sample in July. The printer reached the station in January 2024 and produced the first metal sample made in microgravity later that year. ESA materials specialists at ESTEC compared returned pieces with ground references. The agency says those findings informed an improved procedure used for the two larger elements of the fifth sample.

Two thrusters and two finishing strategies

DLR designed two versions. One was printed as close as possible to the desired final geometry. The other received thicker walls so that its internal diameter could be refined by post-processing after return. The pair tests an important manufacturing trade-off. Near-net-shape printing promises fewer later operations, while machining allowance can provide more control over a critical flow surface.

ESA has not disclosed nozzle diameter, thrust, alloy grade, build time or acceptance tolerance. 'Thruster' therefore means a functionally relevant test article, not a flight-qualified product. Its geometry advances the experiment, but qualification cannot be inferred from its return alone.

What will the vacuum hot-fire test establish?

DLR plans representative hot-fire tests at its vacuum facility in Lampoldshausen. These should show whether the printed articles withstand relevant temperature and pressure and produce the intended operating behaviour. Hot firing is stronger evidence than visual inspection or density measurement because it subjects the component to loads connected to its actual purpose.

Ground controls will be essential. DLR intends to compare equivalent space- and Earth-made components so it can separate manufacturing effects from performance consequences. Useful results require controlled feedstock, geometry, machine condition, heat treatment, finishing and measurement. If the two variants receive different finishing, that variable must also remain explicit.

Why metal printing aboard the ISS is difficult

The system melts and feeds metal in a confined crewed environment. Free particles would make powder handling particularly difficult, so ESA's demonstrator uses wire feedstock. Heat transfer, molten-material behaviour, emissions and process observation can differ in microgravity, while energy, mass, volume and crew time remain scarce.

The goal is not to reproduce a complete terrestrial factory. On long missions, value may come from tools, spares and small functional components whose every possible variant cannot be launched in advance. On-board manufacturing becomes credible only when the combined mass and risk of feedstock, equipment, inspection and finishing compares favourably with carrying finished spares and depending on resupply.

Verified fact, planned test and open questions

The returned fifth sample, the two DLR geometries and the planned Lampoldshausen hot-fire campaign are verified institutional facts. Function, precision and equivalence with ground-built parts remain test objectives rather than completed results. Test timing, protocol, sample count and the path to a qualification-capable successor system have not been published.

Editorial conclusion

The important step is not simply that another metal sample came back from the ISS. The programme has moved from material coupons toward propulsion-relevant geometry. The hot-fire campaign is the decisive next gate. A controlled comparison with public measurement data could show for the first time how microgravity-related manufacturing differences translate into actual component performance.

Sources

- ESA: Tiny thrusters 3D-printed in space — 1 October 2026. - ESA: 3D-printed metal: unlocking crew autonomy — 2 July 2026. - ESA: ESA 3D prints first metal part on the International Space Station — 6 September 2024.