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03 October, 2006

Xenon

On 24th October 1998, the spacecraft Deep Space 1 took off from Cape Canaveral in Florida and headed away from the Earth. As it travelled through the Solar System, the little spacecraft successfully tested a package of 12 different new technologies that might be used in space exploration during the 21st Century. It also rendezvoused with comet Borrelly along the way, and snapped a few pictures. DS1 was powered by an ion propulsion drive which used electric fields to eject a stream of highly-accelerated charged particles. The particles it used were xenon ions and, by an odd coincidence, the launch happened exactly 100 years after xenon was first discovered.

It was the Scottish chemist, Sir William Ramsay who, with Morris Travers, discovered xenon in 1898. Ramsay devoted much of his career to discovering the so-called ‘noble’ gasses (helium, neon, argon, krypton, xenon and radon) and, with Travers and Lord Rayleigh managed to find them all except radon. It was partly for this that Ramsay received the 1904 Nobel Prize for chemistry.

The noble gasses are peculiarly unreactive and tend not to form compounds with other chemicals. That is why they are also known as the inert gasses. This means that the only interest people have in them is largely for themselves and their own peculiar properties rather than the chemistry they take part in. Yet, even so, many laboratories around the world are dedicated to research into some or all of these gasses. Xenon, for example, has found uses in ultra-violet laser technology, electron tubes, bactericidal lamps and various applications in the nuclear industry.
It found its way into space because, for a gas, its atoms are relatively heavy. Once a gas is ionised by stripping electrons off the atoms, it can be pushed around using strong electric fields. Xenon ions can be ejected from DS1’s ion drive at more than 100,000 kilometres per hour using only the power the little spacecraft can generate from it’s own solar panels. It doesn’t produce much force (about as much as you would feel from a piece of paper lying on your hand) but, if it is applied for long enough, the tiny acceleration it creates can push a spacecraft to extremely high speeds.

DS1’s ion drive was turned on two weeks into the mission and the delicate blue haze of its xenon exhaust signalled a new era in deep space exploration, demonstrating a technology that might take us on our first journeys to the stars. It is impossible to believe that Sir William Ramsey could ever have dreamed that the work he did, in an obscure branch of chemistry, would have led us here?

Ultimately, all aspects of the physical world are related through the fundamental laws which govern them. The astonishing power of science is that it can reveal the underlying patterns in the world and uncover these laws. Later, technologists can use these findings - findings from a wide range of different fields of study - to create devices like ion drives that were not even dreamt of a few generations ago.

And that is one of the best arguments I know for letting researchers pursue their own interests rather than be directed by the State into areas that are deemed to have immediate value. We cannot predict what particular pieces of knowledge will prove useful in the future but brilliant and resourceful scientist have the best idea of anyone where they should be probing and how, in order to push back the boundaries of our ignorance.

Give them their head.

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