NASA has embarked on a challenging quest to build a powerful nuclear reactor for long-duration deep space excursions.

As part of the multi-pronged Prometheus Project, engineers and scientists are now tackling plans for the nuclear-powered Jupiter Icy Moons Orbiter (JIMO). This flagship mission using electric propulsion powered by a nuclear fission reactor would showcase a slate of key technologies. It also promises to usher in a new era of solar system exploration.

The amount of power available to JIMO from a nuclear reactor would be hundreds of times greater than on current interplanetary spacecraft.

JIMO's ambitious interplanetary passport -- departing Earth no earlier than 2011 -- calls for orbiting three planet-sized moons of Jupiter: Europa, Ganymede, and Callisto. Each moon may harbor vast oceans beneath their icy surfaces. Loaded down with science instruments, JIMO's tour allows for inspecting the makeup of these moons, their history, and their ability to support life.

The technical hurdles ahead are daunting. So much so, there is a cynical running joke within some corners of the space science community that the icy moons of Jupiter may thaw before JIMO ever shows up.

A JIMO milestone was met this past April with NASA awarding study contracts to Boeing, Lockheed Martin, and Northrop Grumman Space Technologies. Those mission studies are to be completed by year's end.

Early feedback from the trio of contractors is heartening, said Alan Newhouse, Director Project Prometheus, the Nuclear Systems Program at NASA Headquarters.

"I was very encouraged by the breadth of thinking that they are promising us. Whether they deliver of course, we'll know when they do it," Newhouse told SPACE.com .

JIMO does not signal incremental change. It's a "paradigm buster," explains Colleen Hartman, Director of the Solar System Exploration Division within NASA's Office of Space Science.

"This is a huge leap for mankind…not a tiny step," Hartman noted at a Women in Aerospace (WIA) forum on new initiatives in space science held last month in Washington, D.C.

Why the icy moons of Jupiter as JIMO's destination?

"We're following the water. That's one of the main tenants of NASA…because we know that where there is water there is life on Earth," Hartman said. "Is that going to be true throughout the solar system? Frankly, I certainly don’t know. There is energy. There is water. There are organics. There is a possibility of life. So that's why we are endeavoring this icy moons tour," she explained.

Whether or not JIMO winds up slipping year after year due to problems in fabricating a space-rated nuclear reactor is an issue still to be dealt with.

That's the view of Jerry Grey, Director, Science and Technology Policy for the American Institute of Aeronautics and Astronautics (AIAA). "It's not going to be easy. But it's certainly worth doing," he told SPACE.com .

Grey underscores the challenging, long road ahead.

Among issues are special orbit precautions -- putting JIMO into a nuclear safe orbit, to checkout hardware and activate the space reactor high above Earth. Then there's the shielding problem, making sure JIMO's delicate science instruments aren't toasted by the reactor's radiation. Yet another matter is radiating waste heat from the reactor into space.

"One of the biggest concerns in nuclear systems is development and testing," Grey said. Ground facilities for building and checking out new nuclear systems will be costly, take a long time, and involve a high-level of safety precautions, he said.

"And until we do proper testing, we're not going to fly any Prometheus systems," Grey said.

Add to this mix public perception.

"Most of what the public perceives about nuclear systems is wrong…but they perceive it that way. Therefore, you had to deal with it," Grey said.

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