Cape Canaveral, Fla. ? An unmanned NASA spacecraft hurtled toward Pluto on Thursday on a 3-billion-mile journey to the solar system’s last unexplored planet – a voyage so long that some of the scientists who will be celebrating its arrival are just taking their first physics class.

The New Horizons spacecraft blasted off aboard an Atlas V rocket in a spectacular start to the $700 million mission. Though it is the fastest spacecraft ever launched, capable of reaching 36,000 mph, it will take 9 1/2 years to reach Pluto and the frozen, sunless reaches of the solar system.

“God has laid out the solar system in a way that requires a certain amount of patience on the part of those who choose to explore it,” NASA administrator Michael Griffin said.

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 advocates who had feared an accident could scatter lethal radioactive material.

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

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

An Atlas V rocket that will carry the New Horizons spacecraft on a mission to the planet Pluto lifts off from a launch pad at the Cape Canaveral Air Force Station. Thursday's liftoff was just the start of a lengthy journey: The spacecraft is estimated to reach Pluto sometime in 2015.

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

Pluto is the only planet discovered by a U.S. citizen, Clyde Tombaugh, who first saw it in 1930. Tombaugh later received his bachelor’s and master’s degrees from Kansas University.

New Horizons contained some of Tombaugh’s ashes. His 93-year-old widow, Patricia, was in tears as she watched the liftoff from about four miles away.