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A new study from the University of Nottingham has explored the use of fuel-free spacecraft propulsion systems and how they could be used in future space missions.

The , "Modeling and numerical optimization of refractive surface patterns for transmissive solar sails," explores a new class of ultra-light, fuel-free spacecraft propulsion systems. It is published in Acta Astronautica.

Transmissive solar sails steer using sunlight alone, not by reflecting it, but by bending it through microscopic, refractive patterns.

Academics from the Faculty of Engineering and NottSpace research team at the University of Nottingham developed a novel optimization framework to design and evaluate these patterns, achieving significantly improved control and propulsion efficiency. This contributes directly to the development of sustainable, low-impact technologies for future space missions, reducing reliance on onboard fuel and enabling longer-duration operations in deep space.

This work also lays the technical foundation for more ambitious applications such as space-based climate interventions.

Ph.D. student Samuel Thompson said of the project: "For this paper, I developed a ray tracing simulation to characterize and optimize patterned, refractive solar sails to maximize their acceleration and stability. The optics are, on the whole, chaotic and difficult to solve analytically, so I also wrote a reinforcement learning optimizer to run the simulations and iterate upon the designs.

"The appeal of this approach was that the algorithm could be told to optimize according to any criteria; such a sail could be fine-tuned for specific missions and flight regimes, or be rapidly redesigned in response to evolving mission requirements.

"For my Ph.D. project, I used these generative sails to improve upon higher-readiness (non-metamaterial) designs that could see operation soon, and to inform the design of our own NottSpace solar sail prototype. This research is worth expediting because these sails are a highly sustainable propulsion solution, and are even one of the few economically viable means of removing space debris from LEO."

Dr. Cappelletti and Dr. Pushparaj from the NottSpace research team, in collaboration with Technical University of Munich, Germany, and KTH Royal Institute of Technology, Sweden, have contributed to a broader roadmap for a planetary sunshade system, an idea being explored as part of global solar geoengineering efforts. The proposed sunshade system could help reflect or diffuse solar radiation to reduce global temperatures.

Recently, Dr. Cappelletti from the University of Nottingham, was also invited to present this concept at a United Nations event on climate innovation, where she spoke about the potential of solar sail-enabled planetary sunshades as part of future climate resilience strategies.

The team behind this research are also actively integrating these transmissive sails into their in-house CubeSat missions, including WormSail (Astropharmacy Payload in collaboration with School of Pharmacy) and JamSail (GNSS jamming mapper Payload) both 3U platforms currently under development at the University of Nottingham.