A married couple could be sent to Mars in as little as five years' time as part of a private mission backed by the world's first space tourist.
The voyage would take the husband and wife astronauts as close as 100 miles from the surface of Mars, but would not actually land them on the Red Planet.
The expedition would see them cooped up for 16 months in a cramped space capsule.
The project's backers - including US multimillionaire Dennis Tito - intend to use a private rocket and space capsule.