Washington—NASA wants to renew its nuclear power research and development program, as well as restart production lines for electrical generators powered by radioactive plutonium.

Officials said the reason for moving in this direction is that simple, nuclear-powered spacecraft can operate whether or not a planet gets sunlight, and they have a longer life than solar-powered craft.

The solar-powered Mars Pathfinder mission lasted less than three months, but according to Jim Garvin, who heads the Mars exploration program at NASA headquarters in Washington, had the generator been filled with pellets of plutonium, its lifetime might have been years.

NASA’s Galileo and Cassini spacecraft derive electrical power from the natural decay of radioactive plutonium in devices made by the Department of Energy, called radioisotope thermoelectric generators (RTGs). NASA plans to delay launch of a Mars rover from 2007 to 2009 to swap out its planned solar-powered electrical system for an RTG.