Future astronauts may not be able to depend on regular shipments from Earth. For missions lasting months or years—especially crewed missions to Mars—astronauts will need to manufacture tools, replacement parts and other components directly in space.
One promising technology is photopolymer-based manufacturing, which uses light to turn liquid resin into solid objects. It requires relatively little energy, needs compact equipment and offers precise control over where materials are cured.
But researchers have discovered a major problem: the same chemical reaction that hardens the material can generate enough heat to damage the finished product.
A team led by Jonathan Ericson has now investigated this problem through experiments on the International Space Station (ISS), parabolic flights and laboratory testing. Their work has produced a predictive thermal model that could help engineers design manufacturing processes that avoid overheating and defects in microgravity.
Why Manufacturing in Space Matters
The International Space Station, orbiting roughly 400 kilometers above Earth, represents humanity's longest-running large-scale presence in space. Yet even the ISS depends heavily on supplies launched from Earth.
Around 13 metric tons of spare parts are stored aboard the station, while more than 3 metric tons of additional supplies are still required each year.
For future missions much farther from Earth, this approach will become extremely difficult.
A crew traveling to Mars, for example, cannot simply wait for a replacement component to arrive from Earth. Communication itself takes time, and launching large quantities of spare parts is expensive and impractical.
That makes in-space manufacturing an important technology for future exploration.
NASA's In-Space Manufacturing program has been developing different approaches, including conventional polymer 3D printing, robotic extrusion and light-based manufacturing techniques.
Among these technologies, photopolymers are particularly attractive because liquid resin can be stored efficiently and converted into solid components only when needed.
The Heat Problem Nobody Can Ignore
Photopolymerization works by exposing a liquid resin to light, usually ultraviolet light. The light activates chemical reactions that transform the liquid material into a solid polymer.
However, this chemical reaction is exothermic, meaning it releases heat.
On Earth, that heat can be carried away partly through natural convection. Warm material moves, cooler material replaces it and the temperature can be regulated more easily.
Microgravity changes this situation dramatically.
Without normal gravity-driven convection, heat can accumulate inside the curing material. Photopolymer resins also tend to have relatively low thermal conductivity, making it difficult for heat to spread away quickly.
As temperatures rise, several problems can occur. Resins can release volatile compounds, gases can form bubbles and the surface of the material can deform or blister.
The result can be a component that looks fine at first but is mechanically or optically unusable.
A Surprising Discovery on the ISS
The researchers encountered this problem during a 2022 experiment aboard the ISS as part of the RAKIA Ax-1 mission.
Astronaut Eytan Stibbe demonstrated the production of optical lenses using a technique called Fluidic Shaping.
The method takes advantage of microgravity, where surface tension can naturally shape liquid resin into smooth forms. The liquid can then be cured into a solid lens.
The team tested three photopolymers: TJ-3704A, along with two Norland Optical Adhesives, NOA61 and NOA63.
On Earth, all three materials had produced high-quality optical components.
But in orbit, something unexpected happened.
The lenses made from TJ-3704A developed severe blistering on their surfaces. The researchers also observed deformation of the plastic frames and noticeable fumes.
This behavior had not appeared during their earlier ground-based experiments.
The difference pointed toward one major factor: microgravity was changing how the heat generated during polymerization was removed.
Parabolic Flights Confirmed the Hypothesis
Because experiments aboard the ISS are difficult and expensive, the team turned to parabolic flight experiments.
Aircraft flying special parabolic trajectories can create short periods of reduced gravity, allowing researchers to study how materials behave under microgravity-like conditions.
These experiments reproduced the important behavior observed aboard the ISS.
The results linked three factors: microgravity, rising polymer temperature and surface defects.
When natural convection was suppressed, heat accumulated more strongly inside the curing resin. Under the wrong conditions, the temperature increased enough to produce defects.
This demonstrated that thermal management is not a minor detail—it can determine whether a photopolymer manufacturing process succeeds or fails in space.
Building a Computer Model of the Process
The researchers then developed a predictive thermal model designed to simulate what happens inside a photopolymer during curing.
The model combines several important physical processes.
It calculates how heat moves through the material, how much light is absorbed and how the properties of the polymer change as it transitions from liquid to solid.
Light absorption is modeled using the Beer–Lambert law, which describes how light intensity decreases as it travels through an absorbing material.
The model also accounts for heat generated by the polymerization reaction.
This allows researchers to predict how temperature changes over time and how the curing process progresses under different environmental conditions.
Importantly, the model can be adapted for both normal Earth conditions and microgravity by changing the heat-transfer boundary conditions.
The Model Matched Real Experiments
The team first tested the model against laboratory measurements.
The predicted temperature profiles showed strong agreement with experimentally measured temperatures, giving researchers confidence that the model could describe the thermal behavior of photopolymerization.
They then applied the model to the ISS experiments.
The simulations successfully reproduced the blistering observed in the TJ-3704A lenses.
At the same time, the model predicted defect-free outcomes for the Norland optical adhesives under the tested conditions.
This is important because the model is not simply explaining why a previous experiment failed. It can potentially be used before manufacturing begins to determine whether a particular resin, light exposure and environmental condition is likely to produce a successful component.
A Design Tool for Future Space Factories
The researchers envision the model being used as a practical design tool.
Engineers could use it to select suitable polymer properties, light exposure strategies and environmental conditions.
For example, simulations could help determine how intense the UV exposure should be, how quickly curing should occur and how much heat must be removed from the material.
The researchers also found that forced convection could help prevent overheating in the particular manufacturing process studied on the ISS.
That does not mean simply adding a fan solves every space-manufacturing problem. Different manufacturing techniques and materials will have different thermal behaviors.
Instead, the broader lesson is that engineers need to understand and control heat from the beginning of the manufacturing process.
Why This Could Matter for Mars
The implications go beyond producing experimental lenses.
Future spacecraft could potentially manufacture replacement components, tools, optical elements and other useful objects rather than carrying every possible spare part from Earth.
Photopolymer systems are especially interesting because liquid resin can be stored efficiently and transformed into useful solid structures when required.
But scaling these systems up will require reliable control over temperature.
The researchers note that their current model has limitations. It is primarily one-dimensional and assumes uniform illumination and specific light-absorption behavior. More complex manufacturing systems such as DLP and SLA printing could require expanded models that account for nonuniform light patterns and heat conduction in multiple directions.
The model also does not currently include heat loss through evaporation or boiling. These effects could be incorporated in future versions when operation near critical temperatures needs to be studied in greater detail.
Toward Reliable Manufacturing Beyond Earth
The study highlights a problem that could easily be overlooked when bringing manufacturing technologies from Earth into space.
A process that works perfectly on Earth may behave very differently when gravity-driven convection disappears.
For photopolymer manufacturing, controlling the chemical reaction is therefore only part of the challenge. Engineers must also control the heat produced during that reaction.
The new predictive model provides a way to connect material properties, light exposure, heat generation and environmental conditions before an object is manufactured.
That could help transform in-space manufacturing from an experimental capability into a more reliable production technology.
As humanity prepares for longer missions away from Earth, the ability to make what astronauts need, when they need it, using materials already aboard the spacecraft could become one of the foundations of sustainable space exploration.
And before astronauts can build a future space factory, scientists first need to solve something surprisingly simple: how to stop the material from overheating while it is being made.
Reference: Ericson, J., Widerker, D., Stibbe, E. et al. Modeling the thermal behavior of photopolymers for in-space fabrication. npj Microgravity 12, 75 (2026). https://doi.org/10.1038/s41526-026-00612-1
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