Sunlight is all that’s needed to keep these tiny aircraft aloft

Earth’s mesosphere is a “no-fly zone.” The air in this layer of the upper atmosphere is too thin to support traditional aircraft. But new, lightweight devices could defy that rule, requiring only sunlight to keep them aloft on high.

The technology is based on photophoresis, the flow of gas generated around an object when light shines on it. This effect is particularly strong at low pressures, as in the mesosphere, which sits 50 to 85 kilometers above Earth’s surface. Aircraft designed to harness this principle levitated in laboratory conditions that mimicked the mesosphere, physicist Benjamin Schafer and colleagues report in the Aug. 14 Nature. The technique could help scientists unlock the secrets of the mesosphere, which is so poorly understood it’s known as the “ignorosphere.”

Just a centimeter wide, the fliers weigh less than a milligram. Cradling one in your hand feels like holding nothing, says Schafer, of Harvard University and Rarefied Technologies, a startup in Albuquerque, N.M., developing the technology. An errant sigh could send it sailing from your palm. “If you sneeze, you might as well say goodbye.”

The design consists of two thin layers of material stacked atop one another, perforated by channels that allow gas flow — like two slices of Swiss cheese. The top layer is transparent, while the bottom layer absorbs sunlight. This produces a temperature difference that sends gas streaming from the top of the device to the bottom, generating an upward force.

Similar mesosphere surfers have been studied previously, but the new devices generate the largest lift forces for their weight of any tested so far, Schafer says. The researchers estimate that a device with a 3-centimeter radius could hold a 10-milligram payload that could make simple measurements and communicate with the ground.

The devices could provide data on wind speeds, temperatures and pressures in the mesosphere. Or the craft could explore an even more challenging environment: the thin atmosphere of Mars.