Turn satellites into sparkling fireworks to burn up space junk

The chemistry that gives festive sparklers their sparkle could be used to reduce the hazards of falling space junk. Researchers have demonstrated that a mixture similar to that used in fireworks can help bring dead satellites back to Earth safely.

Descending space junk largely ends up in the oceans, but that doesn’t mean we can turn a blind eye to the issue. In 2011, a Delta II rocket stage and a fuel tank came to Earth in Mongolia. Last year an old Chinese rocket stage landed in Myanmar, shaking houses.

“We actually get quite a lot of stuff falling,” said William Ailor at Aerospace, a non-profit company in California that studies orbital debris.

Safely de-orbiting dead satellites or used rocket stages is a serious challenge, and space agencies around the world are working on solutions.

Part of the problem is that a lot of space junk is made of titanium, which has a high melting point: about 1670 °C. Most satellites completely burn up in our atmosphere, but the titanium alloy pieces are more likely to survive re-entry. Even worse, some of these are aerodynamically shaped, making them more likely to reach the ground.

Now, Denis Dilhan at the French space agency and his colleagues have come up with a solution: making metal satellite parts burn up more efficiently as they enter the atmosphere, using thermite – a mixture of metal powder, fuel and metal oxide. Best known for its role in fireworks and welding, it releases heat when ignited.

The team say bits of thermite attached to titanium components would self-ignite when a satellite (or a piece of it) hits the upper atmosphere. That could melt holes in the metal, changing the shape of components and making them more likely to break up.

A team led by Konstantin Monogarov at the Semenov Institute of Chemical Physics in Moscow, Russia, came up with a working thermite formula that would suit this application. To do this, they strapped various types of thermite to some titanium and fired a laser at it.

A mixture of aluminium and cobalt oxide worked best: it took less time to ignite than other formulations, and did so at a lower temperature – down to about 590 °C if the aluminium particles are nano-sized.

It’s a clever idea, says Ailor. If future satellites included thermite, they would need less fuel because there would be no need for a de-orbit burn to put them on what seems a safe trajectory. Apart from there being much less chance of a spent rocket tank or stage ending up in a farmer’s field, use of thermite would save money and effort, too.

But in the real world, a thermite pellet might get shielded from re-entry heat – it might be on the trailing side of the spacecraft, for example – and so have trouble igniting. “The issue is verification,” says Ailor. “How do you know it’s doing what you thought it would?”