A new review published on ScienceDirect by researchers from Xi’an Jiaotong University and the China Academy of Space Technology provides a detailed account of in-space 3D printing progress using polymers and fiber-reinforced composites. The document identifies in-situ additive manufacturing as a transformative approach to fabricating space structures, bypassing launch constraints and enabling rapid production of tools, components, and large assemblies directly in orbit.
Additive manufacturing in space addresses challenges associated with payload mass, onboard spares, and launch geometry. Traditional fabrication methods rely on Earth-based assembly followed by launch, incurring costs exceeding $10,000 per kilogram. Structures are limited in size by payload fairings, and launch overloads require excessive design redundancy. In contrast, 3D printing in orbit allows for lightweight, structurally efficient designs. Thermoplastic polymers, particularly fiber-reinforced variants, are favored due to their low processing temperatures, high strength-to-weight ratios, radiation resistance, and recyclability.
Microgravity and vacuum are two principal conditions affecting printability in space. The review identifies Fused Filament Fabrication (FFF) as the most viable technique under microgravity due to its use of solid filament feedstock and absence of free-flowing liquids or powders. NASA first tested extrusion-based 3D printing aboard a parabolic flight in 1999 using ABS. Subsequent campaigns by Made In Space Inc. (MIS) led to the first on-orbit prints aboard the International Space Station (ISS) in 2014. MIS and NASA produced over 200 parts on ISS using ABS, Ultem 9085, and HDPE.
Experimental comparisons showed negligible mechanical degradation in microgravity-printed specimens. For example, under 1g, ABS specimens exhibited a tensile strength (Xt) of 23.86 MPa, modulus (Et) of 1.52 GPa, and compressive strength (Xc) of 51.37 MPa. Microgravity prints showed Xt of 25.03 MPa, Et of 1.45 GPa, and Xc of 43.37 MPa. Dimensional variation (DV) remained between -0.3 mm and +0.13 mm. PLA parts printed by the European Space Agency (ESA) and German Aerospace Center (DLR) during parabolic flight showed maximum layer heights of 0.26 mm in 0g compared to 0.16 mm on Earth, yet tensile strength remained above 33 MPa in both cases.
The absence of gravity eliminates hydrostatic pressure, disrupting typical material flow. Surface tension becomes the dominant force, increasing the risk of melt fracture and spherical bead formation. A continuity criterion proposed by Crockett et al. established that nozzle height should remain under π times the nozzle diameter to ensure consistent filament deposition. Hafley et al. confirmed that precise nozzle-substrate distance control preserved print continuity in microgravity.
Vacuum conditions introduce thermal control challenges by removing convective cooling. Heat transfer relies on conduction and radiation, slowing cooling rates and altering temperature gradients. Spicer et al. at Virginia Tech developed a vacuum-compatible hotend with titanium heat breaks and radiative heat sinks, maintaining operational stability at 390 °C while keeping feedstock temperatures below 85 °C. Using this system, over 100 functional parts were printed in PEKK, PEI, and carbon nanotube-reinforced variants under 0.01 Pa.
Simulated vacuum tests revealed significant performance differences. PEEK parts printed at 100 Pa exhibited 212.5% higher tensile strength in the V-90 direction compared to atmospheric specimens (10.0 MPa vs 3.2 MPa), indicating improved interlayer bonding. However, H-0 and H-90 SCF/PEEK specimens printed in vacuum showed 6.3% and 29.7% lower tensile strength respectively, due to porosity. Microstructural analysis found 28.91% porosity in vacuum SCF/PEEK compared to minimal levels in pure PEEK, attributed to swelling of closed air pores during extrusion.
Outgassing is a critical constraint. NASA requires TML < 1% and CVCM < 0.1% under ASTM E595. PEKK and PEI reported 0.41% and 0.48% TML respectively, with 0.00% CVCM. PLA, ABS, PETG, PC, and PEEK met the thresholds, while PA exceeded them, making it unsuitable for extended orbital use without formulation changes.
Structural applications of in-space 3D printing focus on two categories: debris shielding and truss frameworks. A variable-density lattice shield developed by Gabriel et al. used Ultem 1010 and 9085, with angled internal panels to deflect debris clouds. In hypervelocity tests, it successfully absorbed a 4 mm aluminum projectile at 5.2 km/s. Spiderfab, developed by Tethers Unlimited, fabricated triangular truss units using SCF/PEEK tapes via heated die pultrusion. A 10-meter truss weighing 340 g was built at 15 cm/min. Redwire’s OSAM system produced a 37.5-meter Ultem 9085 truss using reciprocating push-based deposition. Under vacuum, fabrication of 850 mm segments was validated.
In-space recycling is necessary to maintain material stocks for long-duration missions. The Refabricator, developed by Tethers Unlimited and deployed on ISS in 2018, recycled Ultem 9085 in a closed-loop cycle. After six print/recycle iterations, tensile strength increased by ~10%, though strain at fracture dropped 20%. A second device, Recycler, followed a similar melt-extrusion model.
For fiber-reinforced composites, researchers implemented a reverse melting process using infrared heating. In vacuum (100 Pa), fiber bundles were separated from molten PEEK resin and redrawn into filaments. Remanufactured CCF/PEEK composites showed a tensile strength of 233.8 MPa and modulus of 25.16 GPa—both slightly higher than the original (228.2 MPa and 23.42 GPa). Flexural modulus was 1.5× higher. Microstructural inspection showed improved resin impregnation and reduced voids due to better fiber wetting during remanufacture.
The review identifies four areas requiring further research: accurate simulation of multi-condition space environments, structural design tailored to microgravity stiffness constraints, autonomous on-orbit assembly using robotic systems, and multifunctional structural integration using multi-material printing. Most notably, long-term exposure to temperature swings, atomic oxygen, and radiation—only briefly explored to date—remains a limiting unknown.
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Featured image shows external exposure and post-flight material testing. Image via ScienceDirect.
