It’s a bird, it’s an airplane … no, it is a small, light-powered, floating aircraft designed to operate in the “ignoro atmosphere
Since the 1960s, we have been bringing both craft and people into space, but never a spacecraft has been able to sustain flight in a specific zone of the Earth’s atmosphere called the mesosphere. Sandwiched between the airspace occupied by planes and the upper atmosphere occupied by satellites, the mesosphere is essentially a no man’s land in the border region between Earth and space. Until now.
A team of engineers from the University of Pennsylvania has created a small spacecraft that they say can be done float in the mesosphere, with only sunlight
Why it matters – Built with inexpensive, easily accessible materials such as mylar (a plastic used in some balloons), this near-spacecraft could finally give scientists the chance to explore Earth’s mesosphere. This would provide access to crucial measurements of carbon dioxide that scientists need to accurately track climate change.
The research was published Friday in the journal Science Advances
Here’s the background – Earth’s atmosphere consists of four primary layers:
- Troposphere – the highest layer, up to 375 miles above Earth and home to orbiting observatories such as Hubble (370 miles) and the International Space Station (250 miles).
- Stratosphere – the ozone layer lives here.
- Thermosphere – the layer of the atmosphere, up to 10 miles above the ground, through which planes fly.
- Mesosphere – The middle child of the atmosphere, the mesosphere, lies between the troposphere and the stratosphere, about 50-53 miles above the ground.
In the video detailing the research below, Igor Bargatin, lead author of the study and associate professor of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania, jokingly refers to the mesosphere as the “ ignorosphere. ”
And for good reason.
Here’s why: Because of the pressure that exists above Earth at this height – about 10-30 pascals – this part of the atmosphere exerts too much resistance on satellites, which can cause them to overheat and not provide enough lift for airplanes.
Rockets for their part occasionally pass through the mesosphere on their way out of Earth’s atmosphere, but they never last long.
So the research team decided to try to build a craft that would somehow exceed the needs of planes and satellites by using a different, more natural fuel source: the sun.
Using a process called photophoresis, The same technique responsible for powering light sails, the research team wanted to design a miniature spacecraft capable of continuing to fly in Earth’s mesosphere.
“It’s an exciting idea that you can just shine light on something and make it float and overcome gravity,” Bargatin says in the video.
What they did – The researchers designed a disc-shaped vessel, six millimeters in diameter, with a smooth mylar top and a scratchy carbon nanotube bottom.
The idea, the researchers explain, is that under mesosphere-like pressure, air molecules react differently to these two surface textures. Air molecules will bounce off the scratching bottom of the disc at a higher speed than the smoother top of the disc, creating a net lift that balances or floats the disc in mid-air.
The researchers did their best to mimic the atmospheric pressure and sunlight conditions in their Pennsylvania laboratory, creating an optical light that they could shape and alter to control the movement of the discs.
Why they discovered – In contrast to the team’s previous study, which showed how temperature differences on either side of the discs were also needed for levitation, the new design shows that the same floating effect is possible with the same temperature on both sides.
Not only were their small disks capable of withstanding floating “flight,” but the researchers show in the study that they can carry significant payloads, including scientific instruments many times the disk’s own weight. For vessels like the one in this study, a payload can weigh up to 10 milligrams, which the authors say is enough for the discs to carry a tiny dust or carbon dioxide sensor in the mesosphere.
What’s next – While these initial results are promising, the researchers write that there is still a lot of work to be done before these small crafts can begin to call the mesosphere home. First, this study took place in a controlled laboratory setting, so it remains to be seen if these light-powered spacecraft can actually make it in the real world.
The researchers must also experiment with ways to scale up their technology so that a vessel can hold more than 10 milligrams of cargo at a time. It would also be good to be able to steer and steer the craft if they are also in this forgotten layer of the atmosphere.
Abstract: We report light-guided levitation of nanostructured surface macroscopic polymer films as candidates for long-term near-space flight. We floated centimeter-scale discs made of commercial 0.5 micron thick mylar film coated on one side with carbon nanotubes. When exposed to a light intensity comparable to natural sunlight, the polymer disk heats up and reacts differently with incident gas molecules at the top and bottom, creating a net rebound force. We observed the levitation of discs with a diameter of 6 mm in a vacuum chamber at pressures between 10 and 30 Pa. In addition, we checked the flight of the discs using a shaped light field that optically retained the floating discs. Our experimentally validated theoretical model predicts that the lift forces could be many times the weight of the films, allowing for loads of up to 10 milligrams for sunlight-powered low-cost microflyers at an altitude of 50 to 100 km.