理工学术英语阅读资源库-Reading 5-Passage Two

The Application of Aerogel in Exploring the Solar System

Mark Miodownik

During the summer and autumn of 2002, while in deep space, millions of kilometers from any planet, the Stardust spacecraft opened a hatch and poked out its giant tennis racket fitted with aerogel. It had no opponent in this game of interstellar tennis and the balls it was looking for were microscopically small: the remains of other stars long gone, the leftover ingredients of our own solar system still flying around. The Stardust spacecraft couldn’t hang around in deep space too long because it had an appointment to keep with the comet Wild 2, now hurtling from the outer reaches of the solar system and approaching the center, which it does every 6.5 years. Having withdrawn its aerogel tennis racket, the spacecraft sped off for its meeting. It took just over a year to get to the right position, but on January 2, 2004, the spacecraft found itself on a collision course with the comet, which was five kilometers in diameter and speeding off around the sun. once it had maneuvered itself into the slipstream of the comet, 237 kilometers behind it, the spacecraft opened its hatch and once again poked out its aerogel tennis racket, this time using the B-side, and started to collect, for the first time in human history, virgin comet dust.

Having collected the comet dust, the Stardust spacecraft returned to Earth, arriving back two years later. As it approached the Earth it veered away, jettisoning a small capsule, which fell under Earth’s gravity, entering the atmosphere at a speed of 12.9 kilometers per second, the fastest re-entry speed ever recorded, and so becoming for while a shooting star itself. After fifteen seconds of free-fall, and having reached red-hot temperatures, the capsule deployed a drogue parachute to slow down the rate of descent. A few minutes later, at a height of ten thousand feet above the Utah desert, the capsule jettisoned the drogue chute and deployed the main parachute. At this point the recovery crews on the ground had a good idea of where the capsule was going to land and headed out into the desert to welcome it back from its seven-year, four-billion-kilometer round trip. The capsule hit the sand of the Utah desert at 10:12 GMT on Sunday, January 15, 2006.

“We feel like parents awaiting the return of a child who left us young and innocent, who now returns holding answers to the most profound questions of our solar system,” said the project manager, Tom Duxbury, of NASA’s Jet Propulsion Laboratory in Pasadena, California.

However, until they opened the capsule and started examining the aerogel samples, scientists had no idea whether they held any answers to anything. Perhaps the space dust would have passed straight through the aerogel. Or perhaps the violence and deceleration of re-entry would have disintegrated the aerogel into meaningless powder. Or perhaps there would be no dust at all .

They need not have worried. Once they got the capsule back to the NASA laboratories and opened it up, they found that the aerogel was fully intact and almost completely perfect. There were minuscule puncture marks in the surface and it was these that were subsequently shown to be the entry points for the space dust. Aerogel had done the job and no other material could do: it had brought back pristine samples of dust from a comet formed before the Earth even existed.

Since the return of the aerogel capsule, it has taken NASA’s scientists many years to find the tiny pieces of dust embedded within the aerogel, and the work continues to this day. The dust they are looking for is invisible to the naked eye, and so it must be found by microscopic examination of the samples, which has taken years. The project is so massive that NASA has enlisted the public to help with the search. The scheme Stardust@Hometrains volunteers to use their home computers to look through thousands of microscopic images of the aerogel samples and try to spot the signs that a piece of space dust is present.

The work so far has thrown up a number of interesting results, the most surprising of which is that most of the dust from the comet Wild 2 shows the presence of alumnum-rich melt droplets. It’s very hard to understand how these compounds could have formed in a comet that had only every experienced the icy conditions of space, since they require temperatures of more than 1200 ℃ to do so. Since comets are thought to be frozen rocks that date back to the birth of the solar system, this has come as a bit of a surprise, to say the least. The results seem to indicate that the standard model of comet formation is wrong, or there is a lot more we don’t understand about how our solar system formed.

Meanwhile, having completed its mission, the Stardust spacecraft has now run out of on-board fuel. On March 24, 2011, when it was 312 million kilometers away from Earth, it responded to a final command from NASA to shut down communications. It acknowledged this command, and said its final goodbye. It is currently traveling off into deep space, a kind of man-made comet.

Now that the Stardust mission is over, will this be the fate of aerogel too, to end in obscurity? It is all too possible. Although aerogels are the best insulators we have, they are very expensive and it is not clear that even now we care abut energy conservation enough to value aerogels economically. There are several companies selling aerogel for such thermal insulation applications, but at the moment the main ones are for extreme environments such as drilling operations.

It’s possible that, because of environmental considerations, our energy costs will get higher and higher. In a sufficiently high-cost energy future, it is conceivable that the monolithic double glazing we are all used to may be replaced with a much more sophisticated glass material based on aerogel technology. Research on developing new aerogels has been taking place at an increasingly rapid pace. There are now a number of aerogel technologies that result in a material that is not rigid and brittle, as silica aerogels are, but flexible and bendy. These so-called x-aerogels are made flexible by a neat piece of chemistry that detaches the rigid foam walls of an aerogel from one another and inserts between them polymer molecules that act like hinges within the material. These x-aerogels can be made into flexible materials such as textiles and could be used to make the warmest but lightest blankets in the world, potentially replacing duvets, sleeping bags, and the like. Because they are so light they would also be perfect for outdoor clothes and boots designed for extreme environments. They could even replace the foam soles in sports shoes that make that type of footwear so springy. Recently, a family of carbon aerogels have been created which conduct electricity, as well as super-absorbent aerogels that can suck up toxic waste and gases.

So aerogels may yet be part of our everyday lives, the answer perhaps to living in a more extreme and volatile climate. But although as a materials scientist it’s good to know that we are likely to have the right materials to offer the world in the event that global warming is not averted, this is not the kind of future I want for my children. In a world where we have industrialized so many materials, including those we used to hold sacred, such as gold and diamond, I like to think there may again be a place for a material valued solely for its beauty and significance. Most people will never hold a piece of aerogel in their hand, but those who do never forget it. It is a unique experience. There is no weight to it that you can perceive, and its edges fade away so imperceptibly that it is impossible to see where the material stops and the air begins. Add to this its ghostly blue color and it really is like holding a piece of sky in your hand. Aerogels seem to have the ability to compel you to search your brain for some excuse to be involved with them. Like an enigmatic party guest, you just want to be near them, even if you can’t think of anything to say. These materials deserve a different future, not of oblivion or embedment in a particle accelerator, but to be valued for themselves.

Aerogels were created out of pure curiosity, ingenuity, and wonder. In a world where we say we value such creativity, and give out medals to reward its success, it’s odd that we still use gold, silver, and bronze to do so. For if ever there was a material that represented mankind’s ability to look up to the sky and wonder who we are, if ever there was a material that represented our ability to turn a rocky planet into a bountiful and marvelous place, if ever there was a material that represented our ability to explore the vastness of the solar system while at the same time speaking of the fragility of human existence, if ever there was a blue-sky material — it is aerogel.

Note:

This passage is adapted from the book Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World by Mark Miodownik.

Vocabulary:

aerogel        n. aerogel is a synthetic porous ultralight material deroved from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity.

jettison         v.   to get rid of something or decide not to do something any longer

pristine         adj.  completely free from dirt or contamination

insulator      n.  a material or object which does not allow electricity, heat, or sound to pass through it