Dawn spacecraft has left today Earth and begun its eight years journey to the dwarf planet Ceres and the asteroid Vesta.

At the moment of liftoff, the Delta II's first-stage main engine along with six of its nine solid-fuel boosters ignited. The remaining three solids were ignited in flight following the burnout of the first six. The second stage had put Dawn in a 185-kilometer-high (100-nautical-mile) circular parking orbit in just under nine minutes. At about 56 minutes after launch, the rocket's third and final stage ignited for approximately 87 seconds and Dawn is already on its way to Vesta.

"Dawn, you're on your way. Good luck," Launch Control said once Dawn separated from its third rocket stage.

NASA’s Dawn space program, which costs $343.5 million (not including launch vehicle) and consists of $267 million spacecraft development and $76.5 million mission operations, has received a major setback on July 5, because of heavy thunderstorms above Kennedy Space Center.

Dawn originally was scheduled to fly on June 20 from the Cape Canaveral Air Force Station but the mission was delayed after a crane failure. Then the spacecraft needed minor repairs to one of its solar wing panels.

The Dawn mission will study the asteroid Vesta and dwarf planet Ceres, celestial bodies believed to have accreted early in the history of the solar system.

"Dawn will be history's first mission to go out into the solar system, orbit and explore a distant body, and then go on to a totally different celestial body and explore that one," said Dawn project manager Keyur Patel of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "To do all that you need a spacecraft with a lot under the hood."

The mission will characterize the early solar system and the processes that dominated its formation. Both bodies lie in an orbit between Mars and Jupiter and are building blocks left over from the solar system's formation some 4.6 billion years ago, at the same time and in similar environments as the bodies that grew to be the rocky inner planets, Mercury, Venus, Earth and Mars.

The 1.6-metre long, 747 kilogramme craft is headed for moon.  "The asteroid belt is really fascinating because it's kind of like the boneyard of material that's left over from forming all these planets," said Carol Raymond of NASA's Jet Propulsion Laboratory in Pasadena, California.

"It's fragments of explosions of planetary embryos, perhaps during collisions or material that's come in from other parts of the solar system and been captured into this orbit of the asteroid belt."

Vesta and Ceres were discovered more than 200 years ago, and NASA chose them for their completely different characteristics.

Dawn will first survey Vesta, arriving in October 2011. Vesta is about 500 kilometres in diameter and is the brightest asteroid in the solar system. It can be seen from Earth as a small point of light above the Scorpius constellation. The heavenly body is hot and dry and there are remnants of volcanos.

Six months later, Dawn will leave the heat for icy Ceres. The dwarf planet is 950 kilometres in diameter and its coat of ice is believed to be 100 kilometres thick.

Ceres was the first asteroid to be discovered in our solar system in 1801.

"Ceres likely has a rocky core and a very thick ice mantle," Raymond said. "There's even the possibility that there's liquid water under the surface of Ceres."

"Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Dawn Principal Investigator Christopher Russell of the University of California, Los Angeles. "One is rocky and is representative of the building blocks that constructed the planets of the inner solar system. The other may very well be icy and represents the outer planets. Yet, these two very diverse bodies reside in essentially the same neighborhood. It is one of the mysteries Dawn hopes to solve."

Dawn's launch is the culmination of five years of hopes and fears. NASA at one time scrapped the 449-million-dollar robotic expedition because of high costs and technical problems, before reviving the project last March.

Dawn is also the first US mission on which primary components originated in Europe. Two multispectral cameras that allow the craft to capture images were made in Germany, and the Italian space agency provided the craft's spectrometer.

Dawn is powered by an engine called NASA Solar Electric Propulsion Technology Applications Readiness. Most people in the deep space exploration business just refer to it as "ion propulsion." The juice is, of course, electricity, courtesy of 54 feet of electricity-producing solar array. The gas is xenon, an inert, colorless gas that is four times heavier than air and is the propellant of choice for asteroid explorers everywhere.

Photo: Orbital Sciences Corporation