Cape Canaveral, Fla. ? The ability to explore planets beyond our solar system will require the use of space vehicles with nuclear-powered propulsion systems, NASA Administrator Sean O’Keefe said Tuesday.

Using nuclear power on future spacecraft could cut the time it takes to reach the edge of our solar system from 15 years to five years, O’Keefe told several hundred people attending a space industry conference in Cape Canaveral.

NASA’s past efforts to use nuclear power in space has met opposition from environmentalists. In 1997, hundreds of people protested the launching of the Cassini interplanetary robot craft, which was powered by plutonium.

Developing the new propulsion system has been allotted $3 billion over five years in NASA’s budget and given the name Project Prometheus. Besides making space trips speedier, it would also “enhance the ability of our robotic spacecraft to perform scientific investigations of planets,” O’Keefe said.

If used on manned spacecraft, nuclear propulsion would mean astronauts spend less time in space, reducing the amount of radiation exposure and bone and muscle loss they experience, he said.