A spacecraft that crosses the boundary of plasma at the edge of our solar system could be boosted to the extreme speeds necessary for interstellar travel using a similar principle to how an albatross maintains flight on Earth.
The idea is an extension of a solar sail, which uses a large, reflective surface to 鈥渞ide鈥� the stream of particles being emitted by the sun, gradually increasing in speed over time as particles hit the sail.
Mathias Larrouturou at McGill University in Canada and his colleagues suggest that, rather than using a physical sail, a spacecraft could use magnetic coils to produce a vast electromagnetic field, hundreds of kilometres across.
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This invisible plasma sail would be able to exploit the plasma that streams from the sun at 650 kilometres per second. This plasma extends some 90 times further than the Earth-sun distance, where it collides with particles in interstellar space, creating a boundary called the termination shock. By repeatedly crossing this boundary, the spacecraft could reach tremendous speeds.
鈥淵ou can pick up a large multiple of the solar wind speed, potentially into the neighbourhood of 1 or 2 per cent the speed of light,鈥� says team member at US firm Electric Sky. 鈥淭hat would be two years of continuously going over the termination shock.鈥�
The technique is similar to how an albatross can sustain flight for months by moving between regions of high and low wind to maintain its speed, known as dynamic soaring. Beyond the termination shock, the solar wind drops to less than 200 kilometres per second, so by repeatedly crossing at an angle, a spacecraft could be continuously accelerated by the higher interior wind as it crossed back over. Larrouturou says pairs of magnetic coils would repeatedly push the spacecraft perpendicular to the solar wind as it crossed the boundary, a bit like a boat on Earth tacking in the wind.
Martin Rees, the UK Astronomer Royal and an advocate of interstellar travel, says the idea uses interesting physics, but it isn鈥檛 clear whether the coils could provide enough acceleration to put the spacecraft on a trajectory that took it back and forth over the termination shock. 鈥淚t would be interesting to see some numbers,鈥� he says.
At speeds of 2 per cent the speed of light, a spacecraft could reach our solar system鈥檚 closest star system, Alpha Centauri, in roughly two centuries. And the technology could send more than just simple probes, says Larrouturou. 鈥淭he interactions scale really well,鈥� he says. 鈥淲e think it can achieve human travel.鈥�
Frontiers in Space Technologies
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