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Last Updated: Wednesday, 14 December 2005, 12:17 GMT
Plasma engine passes initial test
Glow from argon plasma.  Image: LPTP, Ecole Polytechnique
The concept exploits a natural phenomenon we see taking place in space
Roger Walker, Esa
The European Space Agency (Esa) says initial testing of a new plasma drive for spacecraft has been a success.

The "double layer thruster" is a new kind of ion drive which could give much more power than existing versions.

It works by accelerating charged particles between two layers of argon plasma, gas where the atoms have been stripped of electrons.

Esa says it has "proven the principle", and will proceed with simulations and perhaps bigger prototypes.

Esa already uses an ion drive on its Smart 1 Moon probe, and the US space agency Nasa deployed one on Deep Space 1, which flew out to Comet Borrelly in 2001.

Different chemistry

The concept is very different from a conventional rocket engine powered by chemical reactions.

Gas is ionised and the ions accelerated in a magnetic field, producing a small thrust.

Although far less powerful than a chemical engine, an ion drive of realistic size can operate for much longer; for deep space missions it may prove a much better option.

The new version of the ion drive concept uses a different way of accelerating ions.

"Essentially, the concept exploits a natural phenomenon we see taking place in space," said Dr Roger Walker of Esa's Advanced Concepts Team.

Smart 1

"When the solar wind, a plasma of electrified gas released by the Sun, hits the magnetic field of the Earth, it creates a boundary consisting of two plasma layers.

"Each layer has differing electrical properties, and this can accelerate some particles of the solar wind across the boundary, causing them to collide with the Earth's atmosphere and create the aurora."

The concept has been developed by Christine Charles and Rod Boswell at the Australian National University (ANU) in Canberra.

Their Helicon Double Layer Thruster uses radio waves to ionise one of the inert, or noble gases - a group which includes krypton, xenon and argon.

Ions are accelerated across the junction between the two plasma layers, creating thrust.

The European team, from Esa and the École Polytechnique in Paris, has now confirmed the Australian findings, and Esa is convinced it could realistically power spacecraft of the future.

Esa believes double layer drives could be as small and economical as the one on board Smart 1, but much more powerful, which would enable craft to accelerate and decelerate faster.

Its next step is to construct computer simulations of the double layer thruster, and then use these simulations in designing larger prototypes.

1. Xenon gas atoms are pumped into a cylindrical chamber, where they collide with electrons from the cathode. The electrons - which are negatively charged - knock electrons off the xenon atoms, creating xenon ions - which are positively charged.
2. Coils outside the chamber create a magnetic field, which causes electrons from the cathode to spiral and become trapped at the mouth of the chamber.
3. The build-up of negatively charged electrons at the mouth of the chamber attracts the positively charged ions, accelerating them out of the chamber.
4. The stream of accelerated ions leaving the chamber thrusts the spacecraft forward. Although the force is small, over time it creates great speed in the frictionless environment of space.

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