After two days of delays, NASA's New Horizons spacecraft executed a picture-perfect liftoff Thursday from Cape Canaveral in Florida on a nine-year journey to Pluto, the last unexplored planet in the solar system.
The spacecraft, which would be the first American probe to visit a new planet since 1977, launched at 11 a.m. Pacific time.
"The spacecraft is where it needs to be, going at the right speed, in the right direction," launch director Omar Baez said.
New Horizons is the fastest craft ever built by the space agency, and is supposed to reach a top speed of 47,000 mph next year by using Jupiter's gravity to slingshot itself into the outer solar system.
It is expected to reach Pluto, the ninth planet in the solar system, in July 2015.
The New Horizons launch capped a successful week for NASA, which on Sunday saw the return of the Stardust spacecraft, bearing pieces of the hamburger-shaped comet Wild 2.
"NASA has accomplished an amazing one-two punch of planetary exploration," said Andrew Dantzler, head of the space agency's solar system division.
It might never have happened. In 2000, NASA canceled the New Horizons program, which had been on the back burner for years. Congress later rescued it, restoring $700 million in funding.
Even as it sat on the launch pad this week, uncertainty reigned.
Scheduled to launch Tuesday, high winds forced a one-day delay. The mission was scrubbed the next day when a power outage struck the Applied Physics Laboratory at Johns Hopkins University, where mission control is located. Clouds delayed the launch Thursday by about an hour.
Launching in January was important for the spacecraft to keep its appointment with Jupiter next year. Continued delays would have forced the craft to go straight to Pluto, costing the mission an extra three years of travel time.
Plumbing the mysteries of Pluto will help scientists understand why the planets formed where they did. New Horizons is also to give researchers a close-up look at the Kuiper Belt, a huge region of icy planetoids that lies beyond Neptune.
The Kuiper Belt was once thought to be a sparse junkyard of castoff planetary parts, but so many new objects recently have been found there that scientists are speculating it may be the remains of a 10th planet torn apart by the forces of the inner planets.
At a news conference after the launch, Alan Stern, the mission's principal investigator, revealed that besides the seven scientific instruments New Horizons was carrying, it also had an unusual piece of cargo: the ashes of Clyde Tombaugh, the astronomer who discovered Pluto in 1930.
Tombaugh, whose widow attended the launch, is the only American to have discovered a planet. That may change soon if the International Astronomical Union certifies Xena, an object discovered last year by a Caltech team, to be a planet. Xena is larger than Pluto.
If all goes according to plan, New Horizons will fly as close as 6,200 miles to Pluto to sample its thin atmosphere and map its unknown surface. So far, the best picture of Pluto has come from the Hubble Space Telescope, which shows a hazy, brownish-red object with bright and dark regions.
The spacecraft's suite of instruments includes a visible light and infrared camera called Ralph, named for Ralph Kramden of the 1950s television comedy "The Honeymooners." It has a long-range reconnaissance imager that will be able to discern objects the size of a football field.
After scrutinizing Pluto, the spacecraft is to take a quick look at its moon, Charon, which is half the size of the planet. From there, it may be redirected toward one or two other Kuiper Belt objects before heading into interstellar space.
"I don't think the final chapter [of the solar system] will be written by this mission," Stern said. "The 21st century will be a bonanza of studies of the deep outer solar system."