ISS Metal 3D Printing Study Targets Melt Defects

ISS metal 3D printing research just gained a new flight project: how tiny metal particles melt and mix when gravity is not stirring the pool. On September 28, 2026, TCT reported that the ISS National Laboratory and the U.S. National Science Foundation commissioned Patricia Weisensee of Washington University in St. Louis to isolate those non-gravitational effects. If powder does not fully melt, metal prints grow defects. This study is the measurement plan, not a finished defect cure.

What's Happening

TCT Magazine’s September 28 report says the ISS National Laboratory and NSF selected two projects that will use the station’s microgravity to study fluid transport. The partnership is more than ten years old. TCT reports that NSF has funded nearly 100 projects through it, leading to more than 350 peer-reviewed papers, in areas that include advanced manufacturing, energy, and healthcare.

Weisensee will lead “The Role of Non-Gravitational Transport Phenomena on the Melting Dynamics of Small Particles.” The question is how metal particles melt and spread through liquid during 3D printing. In metal printing, powder has to melt and mix fully if the solid is going to be uniform. Particles that stay partly solid leave defects that hurt performance. On Earth, gravity drives flows that make it hard to separate surface tension from everything else. In microgravity, the team can watch the non-gravitational piece and build models that Earth experiments keep mixing together. TCT also notes side benefits the same physics could inform, including drug delivery and microplastic recycling, where particles dissolve in liquids.

The second project shares the flight but is not a printer study. Chen Li of the University of South Carolina will measure slip ratio in microgravity flow boiling, where gas bubbles outrun the liquid and change how electronics, refrigeration, and spacecraft cooling reject heat. William Olbricht, deputy head of the NSF Engineering Directorate, and Michael Roberts, chief scientist of the ISS National Lab, framed both selections as access to questions that are hard to ask on the ground. The announcement includes no launch date and no published flight result.

Why ISS Metal 3D Printing Matters Beyond the Station

Most readers will never send a coupon to orbit. The reason the commissioning still belongs in a lab class or a shop discussion is the defect it is trying to explain. Incomplete melting is not a space-only problem. It is why a metal build can look finished and still hide weak planes. A model that says which force moved the liquid, and which force did not, is useful on Earth the day someone trusts it to set laser power, travel speed, or powder feed.

For students, the story is a clean lesson in experimental design. If two forces always act together, you cannot tell which one wrote the result. Gravity is the force you cannot switch off in a campus lab. The station is the switch. Weisensee’s group has already done the Earth half with a transparent stand-in, described below. The flight half is what that stand-in cannot provide: metal-relevant transport without buoyancy dominating the movie.

For a desktop polymer user, the transfer is indirect. Filament printers fail at layer bonds, moisture, and cooling, not at unmelted metal powder. The shared habit is worth keeping: do not treat a successful-looking surface as proof the inside fused. Ask what the process physically had time to do.

What the ISS Metal 3D Printing Flight Still Has to Measure

Question	What Earth studies can already show	What the ISS project is for
Why the melt is hard to see	Metal pools are opaque, so labs use stand-ins such as ice in water (Baskin et al., 2020)	Flight conditions that remove most of gravity’s stirring, per the NSF/ISS brief
What incomplete melting leaves behind	Voids and uneven composition when powder does not fully melt and mix	Models that separate surface tension from buoyancy-driven flow
How low heat creates pores	Lack-of-fusion pores form in track and layer overlaps when heat input is low (Mo et al., 2024)	A check on whether those mechanisms still dominate when gravity is weak
What is not in hand yet	Published analog and review results	No launch date and no station dataset in the September 28 announcement

What the Research Says

Baskin, Flores, and Weisensee filmed roughly 2 mm ice spheres falling into 23–70°C water at 0.8–2.1 m/s as a clear stand-in for powder hitting an opaque metal melt pool. Hotter baths shortened melt time, impact speed had only a minor effect, and unmelted ice rose and finished melting at the surface. They tie incomplete melting and mixing to voids and uneven composition (Baskin et al., 2020). The ice bath is an Earth analog, not a microgravity result.

Mo and colleagues review lack-of-fusion pores in coaxial-powder laser directed energy deposition: irregular voids in track overlaps, layer overlaps, and the bond to the substrate. They tie those pores to low heat input, which leaves a viscous melt that freezes before a tight metallurgical bond can form and can trap gas that cannot escape (Mo et al., 2024). Neither paper reports flight data, and neither qualifies a part for service.

Frequently Asked Questions

What is the ISS metal particle melting study?

The ISS National Laboratory and NSF asked Patricia Weisensee at Washington University in St. Louis to study how small metal particles melt and mix when gravity is not driving the flow. The aim is to explain defects that form when powder does not fully melt in metal 3D printing. Station results are not published yet.

Why study metal melting on the ISS instead of on Earth?

On Earth, gravity drives flow in a melt pool, which makes surface tension and other forces hard to separate. Microgravity on the station reduces that stirring so models can focus on the remaining effects. Weisensee’s lab has already filmed ice particles melting in hot water as a clear stand-in for opaque metal. The flight project has not reported results.

Will this ISS study change settings on a desktop 3D printer?

This project is about metal powder in a melt pool, so it will not retune a home filament printer. A clearer model of incomplete melting could help metal shops predict voids and weak bonds. Filament users should still judge speed against layer adhesion on their own machine. Metal deposition and desktop polymer printing fail for different physical reasons.

Fibricate's Place in This Story

Metal powder has to melt and mix or the part carries hidden planes of weakness. That is a laser-deposition problem. It is a different problem from a desktop polymer print that gets its strength from where continuous fiber is laid. Companies like Fibricate, whose FibreSeeker 3 continuous carbon fiber 3D printer co-extrudes thermoplastic with continuous tow from stock such as the continuous carbon fiber spool, are in that second category. A shop that needs metal in a combustion chamber or a flight fitting is not served by a fiber desktop. A shop that needs a strong polymer tool without a melt pool of powder can stay on the fiber path and leave lack-of-fusion physics to the metal process. Fibricate does not print GRCop, titanium, or station hardware.

What to Watch Next

Watch for a flight manifest, a hardware description, and the first methods paper from the Weisensee team that says what particle size, alloy, and diagnostic they will actually fly. Watch whether models published afterward change how Earth DED groups set heat input, or whether they stay as a microgravity special case. The Li boiling study may move on a different clock and still matter for electronics cooling. Over the next two years the useful signal for classrooms is a before-and-after: analog videos from a water bath, then whatever the station can show once gravity is no longer writing the flow. Until that dataset exists, incomplete melting remains a known defect mechanism, not a solved one.

References & Further Reading

1. Baskin, K., Flores, K. M., & Weisensee, P. B. (2020). Heat transfer and melt dynamics of spherical ice particles impacting a heated water bath. International Journal of Heat and Mass Transfer.
2. Mo, B., Li, T., Deng, L., Shi, F., Liu, W., & Zhang, H. (2024). Mechanisms and influencing factors of defect formations during laser-based directed energy deposition with coaxial powder feeding: a review. Virtual and Physical Prototyping.
3. ISS research effort to explore role of non-gravitational transport phenomena on the melting dynamics of 3D printed metal particles. TCT Magazine. Retrieved September 28, 2026.