Daring to Go There

M. G. Lord's article "Impossible Journey?" [June] was a wake-up call for those eager to rocket into the hostile void of space. But may I beg a big-picture overview here? The age of exploration that made the modern world was bought by the cruel butcher's bill of lost ships, even of completed missions whose crews were decimated by malnutrition, disease, and violence. Those left behind were snuffed out early anyway by the "live squalid, die young" lifestyle. So when we tally the risks of space exploration, we really should compare our potential risk to that of our forefathers who risked far more in giving us the cozy life we have now.

J. Wroblewski
Vancouver, British Columbia

If Mars were habitable, then it would make sense to send humans there, but it isn't, so it doesn't. If it is important to further explore Mars, then spend the money on robotic machines, invulnerable and expendable, to do the job. What knowledge was acquired by humans on the moon that could not have been acquired by ­remote-controlled instruments?

James Hendry
Florissant, Missouri

John Charles, deputy chief scientist at NASA's Space Life Sciences division, responds: Mr. Hendry seems to be asking two important philosophical questions. First, is there any purpose to sending humans to Mars (or anywhere else) if not for permanent habitation? In my opinion, humans can profitably and effectively explore Mars for years or decades without having to live there permanently, so its habitability is not the deciding factor. Second, is there any advantage offered by human explorers that isn't offered by robotic explorers? Given that sending humans will be much more expensive than sending robots, then we must be satisfied that the large extra cost is justified. NASA's current approach is to partner humans and robots, using each to the best advantage. Steve Squyres, principal investigator for the Spirit and Opportunity rovers, says that a robot takes a whole day to do what a human geologist can accomplish in 45 seconds and that the exploration of Mars requires humans on the planet.

Trapped on Earth? Not even close, but you would never know it from this article. There is no mention of experimental programs for checking radiation-quality factors, the importance of dose rate on biological responses, the role that the energy spectrum plays, not even a recognition of the variation in cosmic radiation with the solar cycle—perhaps exploitable to drop an already small hazard by a factor of two or so, just by traveling at the right time. Like anything else in space exploration, the central issue is risk versus reward.

Robert Terry
Columbia, Maryland

M. G. Lord names a way to shield space crews from cosmic rays—surround them with five feet of water—but Earth water isn't practical. I informally submitted a better source to the NASA Institute for Advanced Concepts: Solar-powered robotic bases on the asteroid Ceres could dig out water ice. Mass drivers could launch it slowly but cheaply to other parts of the solar system. Arriving near Earth, this ice could supply water, tritium, hydrogen, oxygen, and so on. We could use what I call a "honeypot ant" spaceship. The ship would basically be a very big balloon made of carbon nanofiber, spinning for gravity, with water inside and air inside that. The crew would live in the central air bubble. Water would simultaneously act as shielding, fuel, and hydroponics/life support. Most of the ship's mass would be Cererian water; Earth would supply the crew, the ship's skin, and the engines. Ceres' surface gravity is about ¹/₃₆ Earth's gravity, and the asteroid is just close enough to the sun for it to power the machinery. Cererian water may unlock the solar system.

Tom Buckner
Asheville, North Carolina