The next launch window is Thursday from 1:08 p.m. ET to 3:07 p.m. ET. NASA has until February 14 to launch the probe.

New Horizons will lift off atop a Lockheed Martin Atlas V rocket from the Cape Canaveral Air Force Station in Florida to begin a 10-year, 3-billion-mile mission to Pluto.

Upper-level winds exceeding 33 knots pushed back the launch numerous times during Tuesday afternoon's launch window.

The New Horizons spacecraft will be the fastest ever launched, more than 10 times faster than a speeding bullet.

About 42 minutes into launch and after it separates from its third stage, New Horizons will speed from Earth at about 16 kilometers per second, or 36,000 mph.

New Horizons will reach a speed of about 47,000 mph (75,600 kph) during its 10-year trip to Pluto. According to The Physics Factbook, a bullet from a large-caliber rifle travels about 5,000 feet (1,500 meters) per second -- about 3,400 mph (5,400 kph).

It took Apollo 11 three days to reach the moon in 1969. New Horizons will fly by it about nine hours after launch and reach Jupiter in a little more than a year, the space agency said.

If all goes as planned, it will then execute a "gravity assist" maneuver, slingshotting around Jupiter to pick up speed.

The maneuver will increase New Horizons' speed to 21 kilometers per second -- 47,000 mph, NASA said.

From there it will travel nine more years in more or less a straight line to Pluto.

The probe, about the size of a baby grand piano, will capture the first up-close imagery of Pluto, its moons and a region of the outer solar system called the Kuiper Belt.

The 10 years it will take New Horizons to reach Pluto will be a long wait for the scientists and engineers who have designed the mission, but they say the payoff will be worth it. (Watch: Mission to Pluto -- 1:28)

"The New Horizons mission is going somewhere no mission has gone before," project scientist Hal Weaver said. "This is the frontier of planetary science."

The Kuiper Belt is a region of icy, rocky bodies that populate a part of the solar system beyond the planet Neptune.

"It is fantastically interesting to me to have a chance maybe within my lifetime for scientists to see up close what those objects look like and to begin our reconnaissance of that region of space," NASA Administrator Michael Griffin said Tuesday morning.

Scientists think the bodies are debris left over from the formation of the planets 4.6 billion years ago. Researchers theorized for decades that such an area probably existed in the solar system, but the first Kuiper Belt object was not identified until 1992.

Since then, hundreds have been found, some of them quite large. Planetary astronomers now believe Pluto is a Kuiper Belt object.

"It's the capstone of the initial reconnaissance of the planets," New Horizons principal investigator Alan Stern said. "It's something that will go down in history, not just for the way it changes textbooks, but for the sort of society we are, that we do these things of lasting historic importance, that we explore beyond our own world."

Weaver said, "This is one of the most important regions of the solar system. It hasn't been explored yet, and New Horizons is going to be the first mission to go out there and look at it up close and personal."

Plutonium to indirectly power craft

With the spacecraft containing 24 pounds of radioactive plutonium-238, the New Horizons launch is somewhat controversial.

The craft is not directly nuclear-powered, but the decay of the plutonium generates heat to fuel a battery, which in turn will power the probe as it moves far away from the sun to the outer reaches of the solar system.

Critics have expressed concern that an accident on launch could spread deadly plutonium over a wide swath of central Florida. (Full story)

In an environmental impact statement NASA was required to file before making final flight plans, the space agency indicated that a 1-in-620 chance exists of an accident on liftoff that would release plutonium into the environment.

As a worst-case scenario, NASA estimated the chances at "1 in 1.4 million to 1 in 18 million" that an "extremely unlikely launch area accident" could release up to 2 percent, or about half a pound, of the plutonium on board the spacecraft.

NASA critic Karl Grossman, author of "The Wrong Stuff: The Space Program's Nuclear Threat to Our Planet," said he doesn't agree with NASA's interpretation of the risks.

"Is NASA again crossing its fingers and hoping?" he asked. "If it's 2 percent or it's 6 percent or if it's 20 percent or if it's 100 percent, when you're talking about plutonium, you're talking about the most toxic radioactive substance known."

New Horizons scientists say the benefits of the project outweigh the risks associated with launch.

"In order for us to continue our exploration of the universe, we have to do these kinds of things," Weaver said.

"The exploration of space, the detailed study of the planets, including Pluto and the Kuiper Belt, are going to be some of the things that people look back on as the achievements of our civilization."

Stern added, "I wouldn't be bringing my friends and family, my children if I thought they were at serious risk."