Satellites to benefit from exploding eggshells

No, really

The European Space Agency (ESA) is reportedly turning to eggshells to help it track orbital debris from spent rocket stages.

This debris, otherwise known as space junk, poses a significant threat to other craft in orbit. Because of the high speed of everything in orbit around Earth, a piece of debris just a centimetre across could cause huge amounts of damage, and could even destroy a satellite.

Since the earliest days of spaceflight, there have been nearly 200 explosions in orbit. At present, 8500 pieces of debris larger than 10cm across are tracked by global space agencies. No one knows exactly how many pieces there are in the 1cm-10cm range, or where they are.

This is where the eggshells come in, New Scientist reports. It turns out that eggshells and spent rocket casings break up in a very similar way. Both break up according to a power law: lots of intermediate sized fragments and few larger ones.

Falk Wittel from the University of Stuttgart in Germany and Ferenc Kun from the University of Debrecen in Hungary, were investigating how eggshells break up in the hope of modelling exploding aircraft. They blew up a more than a few eggshells, and built a computer model of the process.

The eggshell therein is represented by a network of nodes, connected by springs. An explosion inside the shell makes the springs oscillate: if they stretch too far, they break. A broken spring represents a crack. Gradually more and more springs break until the whole shell shatters.

The model allows Wittel and Kun to predict the size of the fragments, and how fast they fly out. Heiner Klinkrad, an expert in space debris at ESA in Darmstadt, saw them demonstrating their experiment on TV and thought that the same model could apply to rocket fuel stages. The information from the model should help the space agencies track down missing pieces of debris.

For those who are curious, the researchers blew up the eggshells by poking holes in the top and the bottom, emptying them of egg, and filling them with hydrogen gas instead. The hydrogen egg is then put in a plastic bag and the escaping gas is lit at one end. Air is sucked in at the other end, and mixes with the hydrogen. Eventually, with a squeaky pop, the eggshell explodes. The plastic bag catches the fragments, and then Wittel and Kun note their number and size. Obvious, when you think about it. ®

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