The first highly compressible yet heat-resistant material for spacecraft heat shields has been developed 鈥� and in early tests, it is proving five times more resilient to vibration and shock damage than any previous material.
Heat shield tiles like those used on NASA鈥檚 space shuttle, which prevented it from being incinerated on re-entry, were often found to be heavily damaged when the spacecraft landed. This made reuse of the shuttle a slow and expensive business.
The damage was due to the fragile nature of the ultralight, ceramic aerogel that the tiles were made of. This material has such low density it is known as 鈥榝rozen smoke鈥� 鈥� its filigree-like structure of silicon dioxide nanoparticles means it weighs only as much as three times the same volume of air.
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But they are utterly miraculous heat insulators: it鈥檚 possible to hold a piece in one hand while blow torching the other side of it, with no ill effects. Still, their fragility has always been their downfall. Until now, that is.
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Spinning jelly
A聽team of chemists led by and at Donghua University in China, have engineered a compressible aerogel that can cope with severe vibration without shattering.
A traditional ceramic aerogel, says Si, is comprised of silicon dioxide nanoparticles strung together like discrete beads on a necklace, which is inherently brittle. Their new aerogel, called a ceramic nanofibrous aerogel, is made from continuous, flexible ceramic nanofibres which are much less prone to snapping.
To make these, the team used a process called sol-gel electrospinning in which silica nanoparticles dissolved in a solvent grow into nanofibres 200 nanometres in diameter. They then link these bendy fibres with molecules of another ceramic material called aluminoborosilicate, which bonds strongly to the fibres. The resulting honeycomb-like material is extremely elastic, says Si.
鈥淚t鈥檚 like a polymer sponge, yet the elastic ceramic remains compressible by as much as 80 per cent, and can still rapidly recover its shape at a temperature of 1100掳C,鈥� he says.
Fly me to the moon
The material could be a boon to China鈥檚 nascent space program, which has the moon and Mars in its crosshairs. On behalf of the China National Space Administration, the Shanghai Academy of Spaceflight Technology has put the material through accelerated ageing tests.
鈥淧reliminary results showed that the service life could increase at least five times than traditional insulation tiles under high vibration conditions,鈥� says Si.
鈥淭his new development appears to offer great promise across a range of potential applications, not least a novel and potentially disruptive solution to the complex challenges of designing space vehicles to return to Earth from orbit,鈥� says Richard Crowther, chief engineer at the UK Space Agency.
鈥淏ut proving the material鈥檚 predictability, survivability and reusability will be the key to its adoption in the safety critical area of space transportation,鈥� he says.
Science Advances
Read more: 2018 preview: Return to the moon as eight missions are planned
