The biggest obstacle NASA faces is money. One critic has called the Constellation program "Apollo on food stamps." During the 1960s, four percent of the entire national budget was spent on space; today one-sixth of one percent goes to NASA.
"The average American's bill, if you will, for the space program, is 15 cents per person, per day," says Griffin. "I don't know about you, but I spend more than that on bubble gum."
And there are worries there could be further cuts. Constellation is a tempting target in a difficult economy. The money squeeze is the main reason why the U.S. won't set foot on the moon until 2020. A Mars landing won't take place until about 2030. To defray costs for the trip to Mars, NASA may need an international partner. If it's up to Congressman Barney Frank, D-Mass., who tried to halt the Mars program, Americans won't be part of any human missions to the planet. So what does he have against Mars?
"I don't have anything against a lot of things I don't wanna spend hundreds of billions of dollars on," says Rep. Frank. "Sending human beings there for the sole purpose of proving that we can do it and bringing them back requires an enormous amount of money at a time when we have a serious deficit, when we are not adequately funding a lot of very important needs right here at home."
Others wonder why NASA doesn't simply continue to send rovers like Spirit and Opportunity to Mars. Miraculously, they not only survived the landing, they have survived for four years on the Martian surface. The rovers were originally supposed to last only three months. The rovers are cheaper and don't put humans at risk. But what rovers can do in a day, humans could do in a minute. And manned missions to Mars could intensify a very important search, according to Squyres, the lead scientist for the rovers.
"We're exploring Mars, fundamentally, because it may once have harbored life," he says. "So, by going to Mars we can address basic questions like, 'How did life first come to be? Is life common or rare throughout the universe?' These are big questions."
Discoveries by the rovers have given hints to the possibilities of life on Mars. Perfect, blueberry-like spheres on the surface are made of a mineral that is often formed in water on Earth. Last year, white dirt appeared in Spirit's tracks. It was silica. The presence of water is required to produce such a high concentration. And inside what's known as the Victoria Crater, Opportunity is finding proof that water once saturated the sub-surface of Mars. Water is the essential ingredient for life.
"This is a big if," Squyres says, "but if you could show that life arose independently on two different planets just in this one solar system, when you consider the multitudes of solar systems that there are out there, it takes no great leap of logic or faith or anything else to believe that life might actually be commonplace throughout the universe."
And if that isn't enough to think about, the real issue may not be whether there was or is life on Mars, but whether there will be life on Mars.
Griffin says, "I think Mars will figure prominently in the future of the human race. Well, I think Mars is in, in the distant future, is another home for human beings."
Human settlements on Mars: is it all just a dream? Will the American public even support traveling to places humans can barely imagine? That may be the biggest question of all.
Produced by Draggan Mihailovich