To boldly go--but not come back: a scientist asks if one-way trips are the only way to realty explore Mars.

• Author: Krauss, Lawrence M.
• Position: SCIENCE

Forty years after Americans first set foot on the Moon, the U.S. space program faces a huge decision: whether we should reach beyond the Moon and send astronauts to Mars.

The biggest challenge to human travel to Mars doesn't involve complicated launching, propulsion, guidance, or landing technologies, but something far more mundane: the radiation from the sun's cosmic rays. The shielding necessary to ensure that astronauts don't get lethal doses of solar radiation on a round-trip to Mars may make the spacecraft so heavy that the amount of fuel needed becomes prohibitive.

But there's a solution: What if we don't bring the Mars astronauts home again?

White the idea of sending astronauts off never to return is jarring, the rationale for one-way trips into space has historical and practical roots. Colonists and pilgrims seldom set off for the New World with the expectation of a return trip, usually because the places they were leaving were pretty intolerable anyway. Give us a century or two and we may turn the whole planet into a place from which many people might be happy to depart.

Moreover, one of the reasons sometimes given for sending humans into space is that we need to move beyond Earth in order to improve our species' chances of survival should something terrible happen back home. This requires people to leave, and stay away.

There are more immediate and pragmatic reasons to consider one-way human space exploration.

First, money: Much of the cost of a voyage to Mars would be spent on coming home. If the fuel for the return trip is carried on the ship, this would greatly increase the mass of the ship, which would then require even more fuel.

If the...