Imagine a lightweight device that does not need propellers, wings, rockets or even a battery to stay airborne. Instead, it could use sunlight and the extremely thin air found high above Earth to generate a lifting force.
That is the idea behind a new class of photophoretic flying structures being explored by Benjamin Schafer and his team. Their work focuses on specially engineered nanofabricated structures that could potentially float in the near-space environment using sunlight.
The concept is particularly interesting because the structures are extremely lightweight. Researchers believe that, with the right design, such devices could eventually carry small sensors and other payloads at altitudes where conventional aircraft cannot operate.
How Can Sunlight Make Something Fly?
The basic principle is called photophoresis. It describes a force that can occur when light interacts with a small structure surrounded by a gas.
At high altitudes, Earth's atmosphere becomes extremely thin. Gas molecules can interact with surfaces in unusual ways because there are relatively few collisions between molecules.
When sunlight heats different parts of a specially designed structure unevenly, gas molecules can leave those surfaces with different amounts of energy. This difference can produce a small force on the structure.
Individually, these forces are tiny. But if a structure is designed correctly and made extremely lightweight, the force can become large enough to counteract gravity.
One particularly promising mechanism is known as thermal transpiration.
The Key Is the Structure
The researchers focused on a design made from two thin, perforated membranes separated by a small distance.
Think of it as an extremely lightweight sandwich. Instead of solid layers, the device contains thin membranes with carefully designed openings. Tiny vertical structures, or ligaments, connect the two membranes.
This architecture is important because the researchers need to solve two problems at the same time.
The structure must be strong enough to maintain its shape, but it must also remain light and allow photophoretic forces to act efficiently.
Making the device stronger generally requires additional material. However, adding too much material increases its weight and makes levitation more difficult.
The researchers therefore used computational modeling to determine how different structural parameters affect the lifting force.
Finding the Optimal Design
The team developed a hybrid analytical–numerical model to investigate how the structure should be designed at different atmospheric altitudes.
Several factors were particularly important.
These included the overall size of the device, the density and arrangement of holes in the membranes, and the distribution of the vertical ligaments connecting the two layers.
The optimal design is not necessarily the same at every altitude.
As altitude increases, atmospheric pressure decreases. That changes how gas molecules interact with the device and therefore changes the photophoretic force.
The researchers used these relationships to identify structures that could provide an effective balance between low mass, mechanical stability and photophoretic performance.
A Clever Compromise Between Strength and Lift
One challenge was that a structure designed purely for maximum photophoretic force might be mechanically fragile.
To address this, the team fabricated structures with a heterogeneous distribution of ligaments.
In simple terms, the tiny supporting elements were not distributed uniformly. Instead, their arrangement was designed to provide structural support where it was needed while limiting unnecessary material elsewhere.
This approach allowed the researchers to compromise between two competing requirements: making the structure rigid enough to survive and keeping it light enough to generate useful lift.
The Experiment
The researchers then tested how the generated lifting force changed with gas pressure.
They performed experiments using gases with three different molecular weights. This allowed them to examine how gas properties influence the photophoretic behavior of the structures.
The results demonstrated that the effect was not merely theoretical.
The team observed photophoretic levitation of a structure approximately 1 centimetre wide at an air pressure of 26.7 pascals.
The structure was illuminated with 750 watts per square metre, which is about 55% of the intensity of sunlight.
This is an important demonstration because it shows that carefully engineered structures can produce enough photophoretic force to overcome their own weight under suitable low-pressure conditions.
Why Near-Space Is Important
The proposed technology is designed for the region of the atmosphere often described as near-space, where the air is far thinner than at Earth's surface.
At these altitudes, conventional aircraft face major limitations. There is not enough dense air for ordinary aircraft wings to operate efficiently, while staying aloft with rockets would require continuous energy.
A photophoretic device could potentially occupy a different operating regime.
It could use sunlight as its energy source and interact with the remaining atmospheric gas to produce lift.
That could create an unusual type of platform capable of remaining at very high altitudes without conventional propulsion.
A Future 3-Centimetre-Radius Device
The researchers also presented a preliminary design for a larger device.
Their concept has a radius of approximately 3 centimetres and is designed around a potential 10-milligram payload capacity at an altitude of about 75 kilometres.
A payload of 10 milligrams may sound extremely small, but modern microelectronics and sensors can be remarkably lightweight.
That means such platforms could potentially carry miniature instruments for scientific measurements.
However, this remains a preliminary design rather than a fully operational flying vehicle. Considerable engineering work would still be required before such a system could be deployed outside laboratory conditions.
More Than Just Vertical Levitation
Simply floating is not enough to make a useful aircraft.
A practical device would also need some way to control its horizontal movement.
The researchers therefore discuss the possibility of horizontal motion control, as well as what happens when sunlight disappears.
At night, the photophoretic lifting force would change or disappear, meaning the device could potentially settle to a lower altitude.
Understanding this overnight settling behavior will be important for designing systems that can operate repeatedly over long periods.
Future designs would need to account for the daily cycle of sunlight and darkness.
Potential Applications
If the technology can eventually be scaled and controlled, these tiny atmospheric platforms could have several applications.
One possibility is climate sensing. Lightweight sensors could potentially monitor atmospheric conditions at altitudes that are difficult to reach with conventional aircraft.
Another possibility is communications. Small floating platforms could potentially act as temporary communication nodes in specialized environments.
The researchers also discuss possible applications in Martian exploration.
Mars has a much thinner atmosphere than Earth, making atmospheric flight challenging. However, the physical principles behind photophoretic forces could potentially inspire new approaches to lightweight aerial exploration there.
Whether the same structures could provide useful lift under Martian conditions would require further research because atmospheric pressure, gas composition, gravity and sunlight are all different from those on Earth.
A New Way to Think About Flight
The most interesting aspect of this research is that it challenges the conventional idea that flying machines need traditional wings, rotors or engines.
Instead, these structures are designed to exploit the interaction between sunlight, extremely thin gases and nanoscale engineering.
The lifting force is small, but the structures are designed to be even lighter.
That balance could eventually allow tiny devices to float in the upper atmosphere using nothing more than sunlight.
The current experiments represent an early demonstration rather than a ready-to-deploy aircraft. Scaling the technology, controlling its movement, surviving changing atmospheric conditions and carrying useful payloads will require further development.
But if those challenges can be solved, photophoretic structures could open an entirely different approach to near-space exploration—one where ultralight materials and sunlight replace conventional propulsion for keeping tiny machines airborne.
Reference: Schafer, B.C., Kim, Jh., Sharipov, F. et al. Photophoretic flight of perforated structures in near-space conditions. Nature 644, 362–369 (2025). https://doi.org/10.1038/s41586-025-09281-8
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