Researchers have created tiny aircraft — each weighing about as much as a fruit fly — that have no moving parts. These flyers are made of plates of nanocardboard and 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.
A study demonstrated nanocardboard's flying and payload-carrying abilities in an environment similar to that of Mars. The thinner atmosphere there would give the flyers a boost, enabling them to carry pay-loads ten times as massive as they are. The weaker Martian gravity would further enhance their capabilities.
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 aluminum oxide walls that are only a few nanometers thick, that corrugation is a regular pattern of channels spanning the plate, which enhances its bending stiffness and prevents 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.
The air current through these microchannels is caused by a classical phenomenon called thermal creep, which is a rarefied gas flow due to the temperature gradient along the channel wall. The researchers measured 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 is important for vetting nanocardboard's potential as a material for atmospheric probes, especially on other worlds including Mars, Pluto, and Neptune's moon Triton. 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.
In addition to carrying sensors, the flyers could simply land and have grains of dust or sand passively stick to them, then transport them back to a 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.