An innovative plasma rocket being built as a spare for one heading to the International Space Station may have a space mission of its own: visiting an asteroid.

Equipped with an electric propulsion system, the rocket, known as Variable Specific Impulse Magnetoplasma Rocket (VASIMR), is being developed to one day transport astronauts to Mars in 39 to 45 days -- a fraction of the six to nine months the trip would take with conventional chemical rockets. Shorter travel time greatly reduces astronauts' exposure to potentially deadly cosmic and solar radiation, currently a show-stopper for human missions to Mars.

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