This story was updated at 5:09 p.m. EST.
NASA's first probe bound for the planet Pluto and beyond rocketed toward the distant world Thursday after two days of delay due to weather.
A Lockheed Martin-built Atlas 5 rocket flung the New Horizons spacecraft spaceward at 2:00 p.m. EST (1900), sending the probe speeding away from Earth at about 36,250 miles per hour (58,338 kilometers per hour)- the fastest ever for a NASA mission. The probe should pass the Moon at 11:00 EST (0400 Jan. 20 GMT) on a nine-year trek towards Pluto.
"The United States has a spacecraft on its way to Pluto, the Kuiper Belt and on to the stars," said New Horizons principal investigator Alan Stern during a post-launch press conference. "I have July 14, 2015 emblazoned on my calendar."
Initial reports indicate that the probe is in good health. Grounds stations received their first signals from New Horizons at about 2:50 p.m. EST (1950 GMT), which showed the spacecraft's radioisotope thermoelectric generator (RTG) - which uses heat from decaying plutonium dioxide to generate power - is online and performing as expected, mission managers said.
"The vehicle looks to be right where it needs to be," NASA launch manager Omar Baez, said just after liftoff. "It was Mother Nature that was holding us back earlier, but we got through it."
Indeed, nature was the bane of New Horizons' launch from the beginning.
Flight controllers were forced to scrub an initial Jan. 17 launch attempt when winds proved too strong at the spacecraft's Complex 41 launch pad at Cape Canaveral Air Force Station in Cape Canaveral, Florida. One day later, severe storms in Maryland prevented a second launch attempt when they knocked out power at New Horizons' mission control center at Johns Hopkins University's Applied Physics Laboratory. The laboratory is managing the mission for NASA.
Earlier today, thick cloud cover repeatedly forced flight controllers to push back New Horizons' planned liftoff from 1:08 p.m. EST (1808 GMT), until the weather eased to meet launch guidelines.
"It was suspenseful, there was no question," Stern said of today's countdown, holding up a small stub of a pencil. "This has been our mascot for years, this little ground-down pencil...it represents perseverance."
New Horizons mission managers took today's launch as an opportunity to honor Pluto's past.
Riding aboard the NASA spacecraft are ashes of the late astronomer Clyde Tombaugh, who discovered the planet in 1930 at the Lowell Observatory in Flagstaff, Arizona. Tombaugh died in Jan. 17, 1997, nine years to the day of New Horizons first launch attempt this week.
"I want to point out what a great honor it is to have Clyde's widow [and family] here with us," Stern said of Patsy Tombaugh, her daughter Annette and son-in-law.
Jim Kennedy, NASA's Kennedy Space Center director, said earlier this week that a Florida quarter - bearing the image of a space shuttle - is also accompanying the probe to Pluto.
Onward to Pluto
The $700 million New Horizons mission began in earnest as the probe popped free from its third stage to begin the long, nine-year trek toward Pluto. The spacecraft should swing past Jupiter, grabbing a gravity boost in the process, in late February 2007, NASA officials said.
"This mission is going to the far frontier of our solar system," said Richard Binzel, a science team co-investigator from the Massachusetts Institute of Technology (MIT), before today's launch. "In some ways, our basic knowledge about Pluto could fit on a three-by-five inch note card."
Pluto is the only member of the traditional nine-planet solar system not visited by a spacecraft, a statistic New Horizons hopes to change. The probe carries seven primary instruments to study Pluto, its moon Charon and two other objects - currently dubbed P1 and P2 - discovered orbiting the planet last year.
The spacecraft is designed to begin observing Pluto about five months before its scheduled flyby in July 2015, which will take place about three billion miles (five billion kilometers) from Earth on the 50th anniversary of Mariner 4's flyby of Mars - NASA's first ever red planet flyby, Stern said.
Mission managers expect New Horizons to speed past the planet at about 31,000 miles per hour while using its instrument package to build detailed maps of the planet, as well as study its composition and tenuous atmosphere.
About nine months after the encounter, the 1,054-pound (478-kilogram) spacecraft should finish sending its Pluto observations to Earth, which will take about 4.5 hours to reach researchers on the ground.
The information New Horizons will send to Earth about Pluto and its moons will likely alter our view of the distant, icy world, researchers said.
"I think it's exciting that all the textbooks will have to be rewritten," Stern said.
Thursday's space shot marked the second Atlas 5 launch for NASA - the Mars Reconnaissance Orbiter flight was the first - and the seventh flight overall for the Lockheed Martin rocket. The launch also marked the second success for NASA this week.
The space agency's Stardust probe - which collected samples of interstellar dust and fragments of Comet Wild 2 (pronounced "Vilt 2") - landed safely on the Utah desert on Jan. 15.
""This week, NASA has accomplished an amazing one-two punch for...exploration," said Andrew Dantzler, director of the solar system division at NASA's Washington, D.C. headquarters. "It's been a great day."
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