Government agencies are powering up to support the effort. U.S. aerospace firms have started assessing how to build nuclear-powered probes. And scientists are sketching out an unprecedented "power-rich" research agenda using potent suites of space science instruments.

Yet Prometheus is not without its detractors. Opponents see the program as dangerous and risky, dismissing it as a front for military star warriors.

In Greek mythology, Prometheus was the wisest of the Titans, and he gave the gift of fire to humanity. The name Prometheus means 'forethought', and true to its name, NASA's space nuclear power initiative was born out of past research with an eye on future innovations.

NASA’s Project Prometheus is targeted at developing two types of nuclear-powered technologies: Radioisotope-based generators and nuclear fission-based systems.

On the one hand, radioisotope power work falls into two camps, a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) and the Stirling Radioisotope Generator (SRG). This hardware is expected to greatly improve on those nuclear power packs used to energize such classic space probes as Pioneer, Voyager, Viking Mars landers, and the Cassini spacecraft now en route to Saturn. This technology would enable "all weather, anywhere, anytime" exploration of planetary surfaces.

But the major poster child for Prometheus is the Jupiter Icy Moons Orbiter, or simply known as JIMO in acronym officialdom.

Prometheus calls for fission power reactor research, advanced heat-to-power conversion hardware, as well as power management and distribution equipment.

Mastery of this technology is embodied in JIMO -- a mission with a wished-for launch in 2011, at the earliest. The spacecraft would orbit three different moons of Jupiter where earlier spacecraft discovered evidence for vast saltwater oceans hidden beneath icy surface layers: Europa, Ganymede and Callisto.

In part, JIMO is a "showoff" mission. That is, NASA wants this Prometheus-push to validate safe and reliable use of electric propulsion powered by a nuclear fission reactor.

"We completely change the way we look at everything if we figure out how to do this," said Sean O'Keefe, NASA Administrator. "What it might do is reveal itself as being the power generation, propulsion solution that ratchets you up, not just incrementally, not just marginally, but exponentially," he told SPACE.com.

O'Keefe said there are different nascent technologies that everybody has great dreams about. But until you finally pour the time, energy, and professional concentration into such an endeavor you won't break out of that dream state.

"This is going to be the catalyst that will get you to that," O'Keefe said. "If we continue to kind of bump along on gravity assists, sling shots, and hope you get the flyby right…you ain't going anywhere," O'Keefe said.

Once on duty, JIMO would set about its science duties. There will be plenty of power to carry out those tasks, O'Keefe explained. Scientists have long flown sensors drawing from miniscule amounts of energy, forcing they to dumb down whole science packages, he said.

What are they going to do with all that extra power on science packages? "They don't know…but they sure like it. That's a liberating aspect of this," O'Keefe added.

Generous gobs of electrical energy would allow radar mapping of the trio of moons, to ascertain the thickness of surface ice on each of the bodies. Additionally, a powerful laser could map surface elevations. An array of sensors, from cameras to an infrared imager and other equipment would be onboard too.

Ronald Greeley, a leading planetary geologist at Arizona State University in Tempe, is very hopeful that the promise of JIMO can be realized. He co-chairs a JIMO Science Definition team, now working to delineate science goals of the orbiter - an activity that should provide a stimulus for the instrument community.

"With nuclear power and propulsion, both the types of missions and the payloads that they can carry open-up significant new possibilities for science," Greeley told SPACE.com.

For one, Greeley said that many of today's space science instruments stand to benefit from additional power without too much development. They include ice-penetrating radar and certain remote sensing instruments. Also, the ability to transmit more data with the extra power is a great boon. Even today, current instruments can take far more data than can be transmitted to Earth, he said.

"The real question is, can new instruments be designed and brought to flight-ready status in time for JIMO? NASA will provide a new source of funding this year geared toward this development, which is very exciting," Greeley noted. "Only time will tell if new payload development can coincide with spacecraft development. Nonetheless, bear in mind that JIMO is the first in a series of similar projects, and now is the time to get the instrument developments underway," he explained.

A major step in building JIMO took place this month. NASA awarded study contracts to Boeing, Lockheed Martin, and Northrop Grumman Space Technologies.

"By next year we will have an idea of what industry thinks they can build," said Alan Newhouse, NASA Director of Project Prometheus, the Nuclear Systems Program. "There are a lot of technical issues. They'll tell us what they think it will cost, whether the mission makes sense, and when they can launch it," he said.

Newhouse told SPACE.com that JIMO is being carried out under NASA's Office of Space Science. While aimed at robotic exploration of the Solar System, could Prometheus lead to human flight beyond low Earth orbit?

"It's something that is in the planning…but not in the execution," Newhouse said.

Regarding space nuclear reactor design work, NASA and the U.S. Department of Energy (DoE) have formed an interagency partnership. "We're still working out the details of whose going to do the work over at DoE. The organization is a little thin to support us, and that's a problem. The whole industry is thin," Newhouse said.

Pushed toward Jupiter on ion engines, JIMO's surveying ability of that planet's icy moons would be extraordinary, Newhouse advised. "The scientists have been thinking for years in terms of watts rather than kilowatts. It's a whole new game," he said.

By converting the reactor's heat to electricity, JIMO could operate with more than 100 times as much power as a non-fission system of comparable weight.

But Newhouse points out that a multitude of tough engineering challenges await solutions. Among them: Large deployable radiators to dissipate heat; long-lived and powerful ion thrusters; power conversion hardware; radiation-hardened electronics; and a long mast between the payload package and the nuclear reactor.

"It's fun…but it is scary," Newhouse said. "I have all of these different tracks that all have to come together at the same time. It'll be one of the biggest spacecraft we've ever built, if not the biggest. It is a challenge to keep it on focus, which is my job," he said.

Early studies of getting JIMO off the ground suggest it would need a boost from an Atlas 5 or a Delta 4 Heavy launcher, Newhouse said. "People ask even today…how can we even think of launching something knowing what happened to Columbia?"

For one, the reactor is launched in a cold shutdown mode. It remains in that mode even if a launch accident were to occur, with the payload striking the water or ground, Newhouse said.

The reactor will have multiple safety features including a design that will prevent criticality while the vehicle is still near Earth. Present plans call for boosting JIMO into a roughly 310-mile (500-kilometer) orbit. From there, it would be nudged out to some 1,240-miles (2,000 kilometers) above Earth.

"We wouldn't run the reactor until we are sure it is headed out, away from the Earth," Newhouse said. "We make sure it's working…and send it on its way," he said.

Rockets lobbed off Earth carrying nuclear reactors on space science pilgrimages is not embraced by everybody.

On May 3, a protest of "NASA Plutonium launches and warfare in space" is slated outside the gates of the Kennedy Space Center in Florida.

Organized by the Global Network Against Weapons & Nuclear Power in Space of Gainesville, Florida, the group wants to call attention to White House intentions to spend nearly $3 billion in the next five years to expand NASA's nuclear space program. Moreover, they argue that any military-run space laser project to control space requires onboard nuclear reactors too.

Also falling under the group's crosshairs are the soon-to-be-launched Mars Exploration Rovers. Each robot is equipped with Radioactive Heater Units (RHUs) to help machinery survive super-cold Martian nights.

In their view, not only are they a danger if they careen back to Earth due to a launch failure. Even if the robots succeed they'll be planting a loathsome nuclear seed on Mars.

"The Mars Rovers will explore the surface of the red planet doing soil identification that NASA hopes will ultimately lead to manned colonies on Mars to mine for uranium, cobalt, magnesium and water. NASA has said that the eventual mining colonies would be powered with nuclear reactors. When the day comes that space mining is profitable NASA intends to turn operations over to the aerospace industry," warns the protest group in a recent news release.