Having conquered the moon long time ago, the NASA [Images] now plans to send astronauts to Mars [Images] -- in what is called a journey which will cover hundreds of millions of miles and no less than two-and-a-half years of roundtrip.

The way to Mars, it seems, is through the moon, says a report in CBS News.

The report says the efforts to send humans back to the moon and beyond has already begun. NASA calls the mission the "most difficult mission ever attempted by the human race".

From the mountains of Utah to the factory floors of Cleveland, from the space center in Houston to the marshes of Virginia, spacesuits are being tested, rockets are being fired, and capsules are being designed, the report says.

"What's impossible? What can't we do if we wanna do it badly enough?" asks Gene Cernan, the last man to walk on the moon. He calls his trip on Apollo 17 a visit to God's front porch. The report quotes him saying as "anything seemed achievable in those days".

"When I came back from the moon in '72, stood on my soapbox and said, 'We're not only going back to the moon, we're gonna be on our way to Mars by the turn of the century. I believed it with my whole heart. But my glass has been half empty for the last 30 years. Now, it's half full," he said.

But according to the report, the project will take time to roll on.  

What will propel the astronauts, the report says, is the new Ares rockets, but they won't be ready until 2015.

Dr. Rick Gilbrech is NASA's exploration chief.

"A lot of people don't understand. They say, 'Why can't we go to the moon, we've already been there.' Well, we can't really roll up the garage door and dust off the Saturn V rockets. That whole infrastructure was dismantled after the Apollo programme."

The decision to break apart Apollo and to cancel possible future trips to places like Mars was made during the Nixon era.

Dr. Mike Griffin, NASA's director, calls that a colossal mistake.

And that mistake, Griffin says, led to the Space Shuttle [Images], which he believes doesn't generate as much excitement because it never leaves the Earth's orbit.

Griffin says Americans are bored by the space programme because NASA has run a boring space project.

There is no question Mars is the ultimate goal, but why return to the moon? Why not go straight to Mars?

The answer is interesting. He says, "If we didn't have a moon, we would. And we could. But it would be much riskier," Griffin says.

To get to Mars, the report says, the astronauts will need to travel several hundred million miles before landing. If something goes wrong along the way, the astronauts would never come back to Earth.

Steve Squyres, the principal investigator for the Mars rovers Spirit and Opportunity, says it is a tough when it comes to Mars, in what he calls a spacecraft graveyard.

Squyres and everyone at NASA were greatly relieved when they landed safely on the red planet four years ago, the report says.

The rovers have been a huge success in exploring Mars and transmitting rare pictures from there. Prior to their landing, roughly two-thirds of all missions to the planet had failed.

If the astronauts land on Mars, Squyres says, they are in store for a hostile environment,  such as radiation from solar flares, dangerous dust and temperatures that average 60 degrees below zero. And they'll have to do it for up to 18 months.

No astronauts, the CBS News report says, have ever spent that amount of time on another world. Neil Armstrong was on the moon for less than a day.

"And I think it's more responsible for us to go to the moon, check out these systems, make sure the life-support systems, the space suits, the little things we need for these long voyages, work properly," Gilbrech says.

This time, NASA wants its astronauts on the moon for weeks, even months, to work out any kinks.

To help essentially colonize the moon, NASA is trying out a new generation of rovers.

The new missions will have the assistance of robonaut, which looks like a cousin of C-3PO, the report says.  A Robonaut is an early model of a robot that might assist the astronauts with routine and dangerous tasks on the moon.

For NASA, the biggest obstacle is funding. During the 1960s, 4 percent of the entire national budget was spent on space. Now only one-sixth of 1 percent goes to NASA.

But nothing deters scientists from thinking ahead.

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."