The fastest spacecraft ever launched began the first full day of its 3-billion mile journey to Pluto, where it will study the last unexplored planet and the mysterious icy area that surrounds it.

The New Horizons spacecraft blasted off aboard an Atlas V rocket Thursday afternoon in a spectacular start to the $700 million mission.

Despite the speed — it can reach 36,000 mph — it will take 9½ years to reach Pluto and the frozen, sunless reaches of the solar system.

"It looked beautiful," said Ralph McNutt Jr. of the Johns Hopkins University Applied Physics Laboratory, one of the mission's scientists. "I was getting a little bit antsy."

The 1,054-pound spacecraft was loaded with seven instruments that will photograph the surfaces of Pluto and its large moon, Charon, and analyze Pluto's atmosphere. Two of the cameras, Alice and Ralph, are named for the bickering couple from TV's "The Honeymooners."

New Horizons also contained some of the ashes of Clyde Tombaugh, the astronomer who discovered Pluto in 1930. His widow, Patricia Tombaugh, was in tears as she watched the launch from four mile away.

"I got emotional. I really did. I just got carried away," said Tombaugh, 93, of Las Cruces, N.M. "It was so beautiful and we've waited so long."

NASA had postponed the liftoff two straight days because of wind gusts at the launch pad and a power outage at the spacecraft's control center in Maryland.

Pluto is the solar system's most distant planet and the brightest body in a zone known as the Kuiper Belt, which is made up of thousands of icy, rocky objects, including tiny planets whose development was stunted for unknown reasons. Scientists believe studying those "planetary embryos" can help them understand how planets were formed.

Some astronomers question whether Pluto is technically a planet. Pluto is a celestial oddball — an icy dwarf unlike either the rocky planets of Mercury, Venus, Earth and Mars or the gaseous planets of Jupiter, Saturn, Uranus and Neptune.

"We're realizing just how much there is to the deep, outer solar system," said Alan Stern, the mission's principal investigator. "I think it's exciting that textbooks have to be rewritten, over and over."

Because it was launched in January, the spacecraft will be able to use Jupiter's gravity as a sling to shave five years off the trip, allowing it to arrive as early as July 2015.

The probe, powered by 24 pounds of plutonium, will not land on Pluto but will photograph it, analyze its atmosphere and send data back across the solar system to Earth.

The launch went off without incident, to the relief of anti-nuclear activists who had feared an accident could scatter lethal radioactive material.

The probe will rely on the natural decay of the plutonium to generate electricity for its instruments.

NASA and the Department of Energy had put the chances of a launch accident that could release radiation at 1 in 350. As a precaution, the agencies brought in 16 mobile field teams that can detect radiation and 33 air samplers and monitors.

"Certainly there are feelings of relief that we didn't have to actually execute any of our contingency plans," said Bob Lay, emergency management director for surrounding Brevard County.

NASA administrator Michael Griffin said he had an answer for those who may question spending $700 million on the mission to a place in space too far away to observe in any detail from Earth.

"Of what value do you think it might be to be able to study the primordial constituents from which the solar system and all the planets and we, ourselves, were formed?" Griffin said.