SCIENCE FICTIONAL HEROES swing a quick jaunt to Mars in a matter of days – or even hours. But that requires rockets that can accelerate all the way without running out of mojo. In the real world of science fact, we can expect travel time to be about nine months, each way. That's a long time to spend cooped up with a small bunch of people. Radiation and weightlessness are also going to make it potentially tough on the travellers' long-term health.
Radiation is the bigger problem. In principle, the solution is simple: make sure the ship's walls are thick enough to block it. But conventional radiation shielding is, unfortunately, heavy.
Ram Tripathi, a researcher at NASA's Langley Research Centre, adds that deep-space radiation doesn't simply plough into shielding and stop, like a bullet hitting a bucket of sand. Rather, it smashes into individual atoms, blasting them into just-as-lethal nuclear shrapnel. "You do not want a heavy material that produces debris," he says.
This makes hydrogen – the lightest of all elements – a prime candidate for shielding because it produces the least, most easily restrained shrapnel. Not that it's possible to build spaceship walls from hydrogen, but in March 2007, at a meeting of the American Physical Society, Tripathi suggested that they could be built of filaments of a material like carbon nanotubes, enriched with hydrogen.
Weightlessness is easier to deal with. One approach is to equip the spaceship with a gymnasium. A full-fledged spa and step classes aren't necessary; all that's needed is some multi-purpose workout widgets like the ones sold on the late-night telly by Chuck Norris. Even better would be to simulate gravity with a spaceship that spins, like a giant gerbil wheel, or is tethered to a burned-out booster engine and swung like a big bolas.
Science fiction author Kim Stanley Robinson, who has spent years thinking about Mars, suggests that during the flight the spin might even be decreased to acclimatise the astronauts to the lower Martian gravity – reducing the risk of unhappy mistakes such as bounding off a cliff when all you intended was to admire the view. On the way home, the ship could be progressively spun up, so the astronauts don't wind up as couch potatoes once they get back.
