Future spacecraft may surf the magnetic fields of Earth and other planets, taking previously unfeasible routes around the solar system, according to a proposal funded by NASA's Institute for Advanced Concepts. The electrically charged craft would not need rockets or propellant of any kind.

Mason Peck of Cornell University in Ithaca, New York, US, has received a grant to study the idea, which is based on the fact that magnetic fields exert forces on electrically charged objects.

He says a satellite could charge itself up in one of two ways – either by firing a beam of charged particles into space, or simply by allowing a radioactive isotope to emit charged particles. The charged satellite would then be gently pushed by Earth's rotating magnetic field, enabling it to change orbit and even escape to interplanetary space.

Early signs suggest the idea may work. In one experiment at Binghamton University in New York, US, Peck's colleague Jim Brownridge connected a small conducting sphere to a piece of radioactive Americium 241 inside a vacuum chamber, successfully charging up the sphere.

But the amount of charge held by a sphere at a given voltage, a quantity known as its capacitance, is not very large. Long, thin filaments, on the other hand, have a lot of charge-holding surface area, so one possible design involves many filaments attached to the spacecraft. The setup would have a rather comical look – because of the static charge, the filaments would stick out in all directions, like newly brushed dry hair.

Radioactive stocking

A cylindrical mesh of fibres – resembling a stocking – could also be attached to the spacecraft. To charge itself up, the stocking could be coated with a radioisotope, and one of the most powerful would be polonium-210, the isotope used to poison former Russian spy Alexander Litvinenko. But it should be safe to use on the stocking, says Peck, "as long as people working on the spacecraft don't lick it".

Radioisotopes provide far more charging power pound-for-pound than a particle beam, which would have to be powered by bulky solar cells. But they present their own technical problems. "We'd like to be able to modulate the charge," says Peck. "But how do you turn off an isotope?" He thinks the solution will involve changing the geometry of the charge-holder to alter its capacitance........Read on.....................http://space.newscientist.com/article/dn11375-spacecraft-may-surf-the-solar-system-on-magnetic-fields-.html

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