An ISS experiment produced nearly 12km of ZBLAN glass fibre, with space-made samples showing 80 per cent greater strength than Earth-made equivalents.
An automated fibre-drawing machine aboard the International Space Station (ISS) has demonstrated how microgravity could improve the mechanical properties of specialised optical fibres. The experiment produced approximately 11.8km of ZBLAN fibre, a fluoride glass being investigated for applications requiring low optical signal loss. Researchers found that the median ultimate tensile strength of space-drawn step-index fibres was 80 per cent higher than that of comparable fibres manufactured on Earth.
The experiment involved Flawless Photonics, which developed the compact drawing system, and researchers from several institutions, including Adelaide University in Australia. The equipment was designed to operate within the ISS’s restrictions on mass, volume, power consumption and astronaut working time. It automated the feeding of glass preforms, drawing of fibres, diameter monitoring and collection of the finished material. This enabled researchers to produce kilometre-scale samples for more detailed comparisons with fibres manufactured under terrestrial conditions.
ZBLAN is a heavy-metal fluoride glass named after its constituent fluorides: zirconium, barium, lanthanum, aluminium and sodium. It is being investigated as an alternative to conventional silica glass for specialised optical applications because of its transmission properties, particularly in the mid-infrared region. Although ZBLAN has the potential to exhibit substantially lower optical attenuation than conventional materials over certain wavelengths, manufacturing defects have prevented commercially produced fibres from consistently achieving their theoretical performance.
One challenge is crystallisation during the drawing process. When glass is heated and pulled into a thin fibre, small crystals can form within the material. These crystals scatter light and increase optical losses. Microgravity provides a different environment for processing molten glass, potentially reducing some of the effects associated with gravity-driven flow and material separation. Drawing fibres in orbit could therefore help researchers investigate whether improved manufacturing conditions produce glass with fewer defects.
The researchers used two types of ZBLAN preforms for their comparison. Single-index preforms contained glass of one refractive index, while step-index preforms had a core and surrounding cladding with different refractive indices. This distinction matters because optical fibres guide light through their internal structure, and the refractive-index difference between the core and cladding helps confine light within the core.
The team produced approximately 11.8km of fibre aboard the ISS and selected about 2.1km of samples with relatively uniform diameters for detailed testing. The samples were compared with fibres manufactured on Earth using a similar drawing system. The researchers assessed optical attenuation, tensile strength and other mechanical properties, allowing them to investigate how the manufacturing environment affected the finished material.
The mechanical results showed that space-drawn fibres had higher median ultimate tensile strength than their ground-manufactured counterparts. The improvement was 25 per cent for single-index fibres and 80 per cent for step-index fibres. The researchers also observed a 39 per cent increase in the Weibull modulus for space-drawn step-index fibres, a measure associated with the consistency and reliability of material strength. These results suggest that the benefits of manufacturing in microgravity can vary according to the fibre structure rather than applying equally to every sample.
Optical performance showed a more nuanced outcome. Space-drawn step-index fibres exhibited lower attenuation than comparable ground-drawn samples, but the researchers did not observe a measurable optical difference between the single-index fibres. The findings therefore do not establish that every type of ZBLAN fibre manufactured in space will transmit light more efficiently. Instead, they indicate that the manufacturing environment and fibre structure both influence the resulting properties.
Despite the encouraging results, manufacturing ZBLAN fibre in orbit does not eliminate all sources of optical loss. Impurities in the starting glass and bubbles trapped in the preforms can still affect the finished fibre. Improving raw-material purity and controlling the manufacturing process remain important requirements before space-produced ZBLAN can be considered for applications demanding extremely low attenuation. Conventional silica fibre is already highly optimised and widely deployed, so ZBLAN must demonstrate a practical advantage in specific applications to justify the additional cost and complexity of orbital manufacturing.
Producing long fibres in orbit is also only one part of the manufacturing challenge. A commercially viable process would need reliable automated equipment, consistent material quality, efficient packaging and a way to return the finished product to Earth. Researchers would also need to establish whether the improvements observed in selected samples can be reproduced at scale. The ISS experiment provides material for evaluating these questions, but it does not yet establish the economics of operating an orbital fibre factory.
For India, the experiment highlights a possible future application for microgravity research as the country develops its own space infrastructure. The planned Bharatiya Antariksh Station is intended to support scientific and technological investigations, including research into space manufacturing. ISRO has identified the first station module for 2028 as part of its broader space programme, although the schedule remains subject to development and mission readiness.
Indian researchers and manufacturers working on optical communications, advanced glass and photonic materials could follow developments in space-based fibre production to identify applications where improved material properties justify specialised manufacturing. However, the experiment does not demonstrate that ZBLAN fibre is ready to replace conventional telecom fibre, nor does it establish that manufacturing it in orbit would be commercially viable in India. Its significance lies in showing that microgravity can improve the mechanical strength of particular fluoride-glass fibres while providing a platform to investigate optical materials that are difficult to manufacture on Earth.
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