No matter how you cut it, lobbing humans to the Red Planet, and keeping them safe, sane, and fit for back-at-home ticker-tape parades is a daring, epic-making sojourn.

Even hurling robots across the vacuum void to Mars has proven hard to do. In fact, there is considerable angst within NASA regarding the landings on Mars of two automated rovers early next year. A two-for-two failure would certainly put a damper on any White House vote of confidence to send humans there.

For one, data on the flux of cosmic radiation reaching the planet's surface is needed. Is there a toxic-to-human chemistry lurking in Martian soil and rock? How troublesome to an expedition are dust-blown particles that might gunk up protective space suits and other life-sustaining hardware?

These are among a number of near-term knowledge gaps points out James Garvin, NASA Lead Scientist for Mars Exploration in the space agency's Office of Space Science in Washington, D.C.

Without this wisdom, and additional data points squarely in head and hand, space engineers, life science specialists, and others could be forced to over-design a humans to Mars effort by factors of 10, Garvin said. A paucity of particulars would surely add to total mission cost.

Garvin points out that NASA's current Mars Exploration Program -- while now all robotic -- does have one research focus firmly centered on supporting future flesh and bone, on-the-spot examination of the Red Planet. And that is to obtain the required environmental knowledge about Mars such that human explorers can tromp across Mars with both a high degree of safety and cost effectiveness.

Much work remains to be done on the kinds of deep space flight systems, the habitats, life support equipment, information technology needs, as well as issues concerning long-haul human adaptation to space, Garvin suggests.

"Our current program of orbital and soon in-situ reconnaissance will provide some of the elements needed for proper systems engineering and development of human-rated systems needed for Mars," Garvin stated.

Now on the books is a string of NASA robots that will attack Mars on various fronts.

Already en route are the Spirit and Opportunity rovers. They will wheel and deal with Mars beginning in January. Those missions are to be followed by a Mars Reconnaissance Orbiter launch in 2005, the Phoenix lander in 2007, and a Mars Science Laboratory in 2009, a probe now intended to roll across the planet carrying an array of super-slick science gear.

An in-house cadre of NASA Mars thinkers is now busily hammering out a strategy for next decade robotic exploration of that faraway world.

"Mars beckons, it is true," Garvin noted, "but to optimally design human-rated systems to allow for people to undertake expeditions to the Red Planet may require another decade of intensified environmental measurements."

Doing so will facilitate better systems engineering and design solutions for safe, cost-effective human-based exploration of the exciting Red Planet, Garvin said.

While both the Moon and Mars have their backers and detractors, another objective is gaining ground -- and high ground at that.

"The only religion I will ever have is planetary defense…using space to protect Earth," said noted author and New York University journalism professor, William Burrows. "For the first time in all of history, access to space allows us to protect ourselves."

Not only can Earth-threatening asteroids be thwarted, Burrows said. But also access to space can help short-circuit weapons of mass destruction proliferation, pollution, nasty weather, resource depletion, and more.

Burrows has just completed a book called The Survival Imperative: Using Space to Protect Earth. To make his case he draws three threads together. First, NASA is adrift without an apparent purpose. Secondly, Earth is a fragile planet increasingly beset by dangers, both from self-inflicting wounds and by nature itself. Lastly, a disaffected youth increasingly has no sense of joy of purposeful adventure.

Taken collectively, Burrows suggests, these dreadful threads lead to a single, majestically important solution of using space to protect Earth. As he sees it, "planetary defense should become NASA's overarching, completely focused, goal." This plan involves active defense; starting a continuously updated cultural archive at places on Earth and on the Moon; and migration outward by returning to the Moon and building large stations.

"Access to space for the first time gives us the wherewithal to defend ourselves against multiple calamities," Burrows said. "As the saying has it: If the dinosaurs had had a space program, they would still be here."