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Space junk is a huge problem. The surge in satellite launches in recent years is leaving low Earth orbit (LEO) cluttered with debris such as discarded rocket bodies, broken parts and defunct satellites. Beyond the risk of debris colliding with working satellites that are vital for navigation, communication and weather forecasting, large pieces could come crashing back down to Earth.

Space junk may also be a threat to the environment. Old rockets and satellites burn up when they re-enter the atmosphere, leaving a trail of chemicals behind that could damage the ozone layer. The more we launch, the messier LEO gets, and the bigger the problems become.

Space agencies and private companies are looking at ways to clear up the litter we leave behind, but they're also exploring how to build more sustainable rockets and satellites, using organic polymers instead of metals. In a new study, in Acta Astronautica, researchers turned to origami, the ancient Japanese art of paper folding, to find a sustainable alternative.

Paper planes in space

Maximilien Berthet and Kojiro Suzuki from the University of Tokyo wondered what would happen if a paper plane were launched from the International Space Station (ISS) at a height of 400 kilometers and a speed of 7,800 meters per second, similar to that of the orbiting station. They wanted to know how long it would take to fall back into the Earth's atmosphere and how much heating it could endure, among other things.

Initially, the plane remained stable due to the way it was folded, gliding smoothly in the vacuum-like conditions of space, according to the software simulations. But then after four days, when it reached about 120 kilometers above the Earth, things took a different turn. The plane tumbled and started to spin out of control.

"The paper space plane's extremely low rotational inertia and aerodynamic static margin enable it to passively maintain a stable flow-pointing orientation for most of atmospheric entry," explained the researchers in their paper.

"Below around 120 km altitude, tumbling motion is expected, accompanied by severe aerodynamic heating resulting in burn-up in the atmosphere at around 90–110 km altitude."

Â鶹ÒùÔºical model

Berthet and Suzuki also built a physical model of their plane made from paper with an aluminum tail. They put it into the Kashiwa Hypersonic and High Enthalpy Wind Tunnel at the University of Tokyo to see how it would hold up under conditions similar to re-entry. They subjected it to Mach 7 for seven seconds, during which the nose bent back, and there was some charring on the wing tips, but it didn't disintegrate. However, it would have burned up had the experiment gone on for longer.

One small step

This research shows how a simple idea could inspire a more sustainable approach to tackling the problem of space debris. The study's authors also suggest paper-based spacecraft could play a role in future missions, such as gathering data about the Earth, then burning up completely without leaving harmful material behind. It's a small step, but one that could make our forays into space better for the environment and safer for us down on the ground.

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