Now that the hype surrounding the 40th anniversary of the Moon landings has come and gone, we are faced with the grim reality that if we want to send humans back to the Moon the investment is likely to run in excess of $150 billion. The cost to get to Mars could easily be two to four times that, if it is possible at all.

This is the issue being wrestled with by a NASA panel, convened this year and led by Norman Augustine, a former chief executive of Lockheed Martin, that will in the coming weeks present President Obama with options for the near-term future of human spaceflight. It is quickly becoming clear that going to the Moon or Mars in the next decade or two will be impossible without a much bigger budget than has so far been allocated. Is it worth it?

The most challenging impediment to human travel to Mars does not seem to involve the complicated launching, propulsion, guidance or landing technologies but something far more mundane: the radiation emanating from the Sun’s cosmic rays. The shielding necessary to ensure the astronauts do not get a lethal dose of solar radiation on a round trip to Mars may very well make the spacecraft so heavy that the amount of fuel needed becomes prohibitive.

There is, however, a way to surmount this problem while reducing the cost and technical requirements, but it demands that we ask this vexing question: Why are we so interested in bringing the Mars astronauts home again?

While the idea of sending astronauts aloft never to return is jarring upon first hearing, the rationale for one-way trips into space has both 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 that is sometimes given for sending humans into space is that we need to move beyond Earth if we are 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 missions.

First, money. Much of the cost of a voyage to Mars will be spent on coming home again. If the fuel for the return is carried on the ship, this greatly increases the mass of the ship, which in turn requires even more fuel.

The president of the Mars Society, Robert Zubrin, has offered one possible solution: two ships, sent separately. The first would be sent unmanned and, once there, combine onboard hydrogen with carbon dioxide from the Martian atmosphere to generate the fuel for the return trip; the second would take the astronauts there, and then be left behind. But once arrival is decoupled from return, one should ask whether the return trip is really necessary.

Surely if the point of sending astronauts is to be able to carry out scientific experiments that robots cannot do (something I am highly skeptical of and one of the reasons I don’t believe we should use science to attempt to justify human space exploration), then the longer they spend on the planet the more experiments they can do.

Moreover, if the radiation problems cannot be adequately resolved then the longevity of astronauts signing up for a Mars round trip would be severely compromised in any case. As cruel as it may sound, the astronauts would probably best use their remaining time living and working on Mars rather than dying at home.

If it sounds unrealistic to suggest that astronauts would be willing to leave home never to return alive, then consider the results of several informal surveys I and several colleagues have conducted recently. One of my peers in Arizona recently accompanied a group of scientists and engineers from the Jet Propulsion Laboratory on a geological field trip. During the day, he asked how many would be willing to go on a one-way mission into space. Every member of the group raised his hand. The lure of space travel remains intoxicating for a generation brought up on “Star Trek” and “Star Wars.”

We might want to restrict the voyage to older astronauts, whose longevity is limited in any case. Here again, I have found a significant fraction of scientists older than 65 who would be willing to live out their remaining years on the red planet or elsewhere. With older scientists, there would be additional health complications, to be sure, but the necessary medical personnel and equipment would still probably be cheaper than designing a return mission.

Delivering food and supplies to these new pioneers — along with the tools to grow and buildwhatever they need, for however long they live on the red planet — is likewise more reasonable and may be less expensive than designing a ticket home. Certainly, as in the Zubrin proposal, unmanned spacecraft could provide the crucial supply lines.

The largest stumbling block to a consideration of one-way missions is probably political. NASA and Congress are unlikely to do something that could be perceived as signing the death warrants of astronauts.

Nevertheless, human space travel is so expensive and so dangerous that we are going to need novel, even extreme solutions if we really want to expand the range of human civilization beyond our own planet. To boldly go where no one has gone before does not require coming home again.

Lawrence M. Krauss, the director of the Origins Initiative at Arizona State University, is the author of “The Physics of ‘Star Trek.’” Below is an article he wrote, originally published in The New York Times on August, 31, 2009.

 

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