A light spaceship bound for the no man’s land of space

It’s a bird, it’s a plane … no, it’s a small, light, levitating plane designed to fly in the “ignoro-sphere.“

We’ve been putting both crafts and humans in space since the 1960s, but never Was a spacecraft able to sustain flight in a specific area of ​​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 liminal region between Earth and space. Until now.

A team of engineers from the University of Pennsylvania have created a small spacecraft that they believe can levitate in the mesosphere, using only sunlight.

Why is this important – Built using inexpensive and easily accessible materials like mylar (a plastic used in some balloons), this near-space spacecraft may finally offer scientists the opportunity to explore the Earth’s mesosphere. This would provide access to crucial measurements of carbon dioxide, which scientists need to accurately monitor climate change.

The research was published in the journal Friday Scientific advances.

Here is the background – The Earth’s atmosphere is made up of four primary layers:

• Troposphere – the highest layer, up to 375 miles above Earth and is 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, that planes travel through.
• Mesosphere – Child of the middle of the atmosphere, the mesosphere lies between the troposphere and the stratosphere, about 31-53 miles above the ground.

In the video describing 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: Due to the pressure that exists at this height above Earth – around 10-30 Pascals – this part of the atmosphere exerts too much drag on the satellites, which can cause them to overheat, and not enough lift for airplanes.

Rockets, on the other hand, sometimes pass through the mesosphere on their way out of the Earth’s atmosphere, but they never stay for long.

The research team therefore decided to try to build a device that could go beyond the needs of planes and satellites by using a different and more natural source of fuel: the Sun.

Using a process called photophoresis, Using the same technique responsible for powering light sails, the research team set out to design a miniature spacecraft capable of maintaining flight through Earth’s mesosphere.

“It’s an exciting idea, that you can just light something up and make it float and overcome gravity,” Bargatin says in the video.

What did they do – The researchers designed a disc-shaped craft, six millimeters in diameter, with a smooth mylar top and a rough carbon nanotube bottom.

The idea, the researchers explain, is that air molecules at a pressure similar to the mesosphere react differently to these two surface textures. The air molecules will bounce off the rough bottom of the disc with a higher velocity than the smoother top face of the disc, creating a net lifting force that balances or levitates the disc in mid air.

The researchers did their best to recreate the atmospheric pressure and sunlight conditions in their Pennsylvania lab, creating an optical light trap that they could shape and modify to control the movement of the discs.

Why they found out – Unlike the team’s previous research, which demonstrated how the temperature differences on either side of the discs were also necessary for levitation, the new design shows that the same levitating effect is possible with the same temperature on both sides.

Not only were their tiny disks able to withstand levitating “flight”, the researchers show in the study that they can carry large payloads, including scientific instruments many times the weight of the disks. For trades like those in this study, a payload could weigh as much as 10 milligrams, which the authors say is enough for the disks to carry a small catcher of dust or carbon dioxide into the mesosphere.

And after – While these early results are promising, the researchers write that there is still a lot of work to be done before these tiny contraptions can start calling into the mesosphere. On the one hand, this study took place in a controlled laboratory, so it remains to be seen whether these light spacecraft can actually be successful in the real world.

Researchers are also to experiment with ways to evolve their technology so that a craft can hold more than 10 milligrams of cargo at a time. It would also be good to be able to direct and control the craft once it is in that forgotten layer of the atmosphere.

Abstract: We report the light levitation of macroscopic polymer films with nanostructured surfaces as candidates for long duration near space flight. We levitated centimeter-scale disks made of a 0.5 micron thick commercial mylar film coated with carbon nanotubes on one side. When illuminated with a luminous intensity comparable to natural sunlight, the polymer disc heats up and interacts differently with the gas molecules incident on the upper and lower sides, producing a net recoil force. We observed the levitation of 6 mm diameter disks in a vacuum chamber at pressures between 10 and 30 Pa. In addition, we controlled the flight of the disks using a shaped light field that trapped optically levitating disks. Our experimentally validated theoretical model predicts that lift forces can be several times the weight of films, allowing payloads of up to 10 milligrams for low cost sunlight-powered microflyers at altitudes of 50-100 km .