There's a growing chorus of calls to send astronauts to Mars rather than the moon, but critics point out that such trips would be long and gruelling, taking about six months to reach the Red Planet. But now, researchers are testing a powerful new ion engine that could one day shorten the journey to just 39 days.
Traditional rockets burn chemical fuel to produce thrust. Most of that fuel is used up in the initial push off the Earth's surface, so the rockets tend to coast most of the time they're in space.
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