Nanocardboard flyers could explore Martian atmosphere

The so-called nano-cardboard flyers, each weighing about as much as a fruit fly, levitate when bright light is shone on them. As one side of the plate heats up, the temperature differential gets air circulating through its hollow structure and shooting out of the corrugated channels that give it its name, thrusting it off the ground.

According to a study on the technology published in the journal Advanced Materials the thinner atmosphere in a Martian environment would give the flyers a boost, enabling them to carry payloads ten times as massive as they are. The weaker Martian gravity would further enhance their capabilities.

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According to Igor Bargatin, lead researcher on the project, the technology could offer an alternative to more complex probes like the Mars Helicopter, that will be carried aboard NASA Perseverance Mars Rover.

"The Mars Helicopter is very exciting, but it's still a single, complicated machine," said Bargatin, “If anything goes wrong, your experiment is over, since there's no way of fixing it. We're proposing an entirely different approach that doesn't put all of your eggs in one basket."

Bargatin's group has been experimenting and improving on their nanocardboard design since 2017. Inspired by the common paper packaging material, they collaborated with researchers at the Singh Center for Nanotechnology to achieve a record-setting ratio of weight and stiffness, as reported in a recent Nature Communications paper.

Like paper cardboard and other "sandwich structured composites" used in architecture and aviation, nanocardboard's material properties stem from corrugation. Consisting of a hollow plate of aluminium oxide walls that are only a few nanometers thick, that corrugation is a regular pattern of channels spanning the plate, which enhance its bending stiffness and prevent cracks from propagating.

These channels are also responsible for the plates' ability to levitate, as creating a temperature differential generates an air current that flows through their hollow structure.

Their recent study allowed the researchers to measure the flyers' ability to lift mock payloads -- silicone rings, attached to the top of the plates -- thanks to a new low-pressure test chamber with integrated cameras and light sources.

Studying these dynamics are important for vetting nanocardboard's potential as a material for atmospheric probes, especially on other worlds, including Mars, Pluto and Neptune's moon Triton. Because Bargatin's nanocardboard flyers weigh about a third of a milligram, it would take more than a million of them to equal the mass of the Mars Helicopter, and more than six billion to equal the ground-based rover that will deploy it.

But even in the ideal environment of the Martian atmosphere, the tiny flyers would still be limited to sensors and payloads that are at most a few milligrams. As such, Bargatin is now collaborating with other researchers on how to miniaturize chemical sensors that could detect water or methane -- key signatures of life on Mars.

"In addition to carrying sensors," Bargatin says, "our flyers could simply land and have grains of dust or sand passively stick to them, then transport them back to the rover so it doesn't need to travel as far."

The rover could also provide a means of piloting the nanocardboard flyers. Despite having no moving parts, they can be steered by way of a pinpoint laser, since the direction of the air flowing out of their channels depends on which parts of the plate are heated.