Tim Radford
United States space scientists believe they will be able to conjure up refrigerator and furnace insulation tiles out of thin air.
They are experimenting with a composite material called aerogel, the lightest solid known. A lump of this “frozen smoke” the size of a man would weigh less than 0,45kg, but could bear the weight of a car.
The stuff, made of silica, alumina and carbon, can weigh less than the same volume of air. It was tested on the robot rover on Mars last year, and on a shuttle flight this year. It may also play a part in an experiment called Stardust, under which a robot spacecraft will fly through a comet and collect its dust.
But Nasa researchers in California have more practical things in mind. Spacecraft work in an environment far colder than anywhere on Earth. But the space shuttle has to return through the upper atmosphere at colossal speeds – and at 1 100 C or more. Insulation is a big problem.
“Solid smoke, or aerogel, works like a vacuum layer because it is a great insulator,” said Dr Susan White, of the Nasa Ames Research Centre at Moffet Field. “The new aerogel tiles can insulate spacecraft from 10 to 100 times better than today’s tiles.”
The idea of “frozen smoke” is an old one – it was developed at Stanford University in California 60 years ago – but only recently have scientists been able to make the stuff in useful quantities.
Researchers at Nasa’s Marshall Space Flight Centre in Huntsville, Alabama, have been contemplating using it for window material.
The catch is that – so far – the material is opaque. But if light cannot get through, nor can heat. A 2,5cm-thick sheet has about the same insulation value as 15 panes of glass and trapped air. The sandwich of aerogel in the space shuttle tiles is filled with a tangle of “strings of pearls” each a billionth of a metre across. This creates so many sides and surfaces that a 2,5cm-thick cube of the stuff could, if unfolded, cover a tennis court.
“The reason the aerogel tile composite will act as a great insulator for keeping freezers cold, or automobile catalytic converters hot, is that the air flowing through the tile is almost completely blocked by aerogel,” said Dr White. “It is like having a chunk of solid vacuum where you need it.”
Aerogel has, so far, been a space technology solution in search of a problem. It is brittle, so on its own it cannot be machined.
But insulation tiles filled with a layer of it can be cut, shaped, drilled and attached to any surface. The Ames scientists believe it could be used to line furnaces, contain cold substances such as liquid oxygen or nitrogen, or protect spacecraft from icing up on the launch pad.