The "Dawn" Of Asteroid Exploration

A Delta 2 rocket boosted NASA's $357 million Dawn spacecraft into space early Thursday, kicking off a decade-long flight to orbit and map the two largest members of the asteroid belt between Mars and Jupiter.

The United Launch Alliance Delta 2, equipped with nine strap-on solid-fuel boosters, roared to life at 7:34 a.m. and climbed away from launch complex 17B at the Cape Canaveral Air Force Station atop a brilliant jet of flame and a cloud of churning exhaust, reports CBS News space consultant Bill Harwood.

It's a three-billion-mile, eight-year journey.

Liftoff was delayed 14 minutes because of a boat that strayed into the offshore launch impact danger zone and then to make sure the rocket did not fly too close to the international space station.

Dawn will travel to the two biggest bodies in the asteroid belt between Mars and Jupiter - rocky Vesta and icy Ceres from the planet-forming period of the solar system.

"They're two of the largest asteroids in the main asteroid belt, but also they're every different from each other," NASA engineer Jennifer Roca said.

Ceres is so big - as wide as France - that it has been reclassified a dwarf planet. Vesta is about the length of Poland.

"We should learn a lot about the evolutionary history, the geologic makeup, and, of course, take stunning visual images throughout the orbital phases," Roca told CBS News correspondent Peter King earlier this week.

The initial stages of the flight appeared normal as the solid-fuel boosters burned out and fell away, followed by first stage shutdown four minutes and 22 seconds after liftoff. The rocket's second stage then boosted the probe into space.

The flight plan called for a short second stage burn 51-and-a-half minutes after launch and ignition of a solid-fuel third stage motor a few minutes later. Spacecraft separation, the final event in the launch sequence, was expected 62 minutes after liftoff.

Dawn will accelerate at a snail's pace, reports King, taking four days to go from zero to 60 mph, in order to conserve fuel.

It will take engineers nearly three months to activate and check out Dawn's systems and its innovative ion propulsion system, the technology that makes the unprecedented flight possible.

The Delta 2 rocket put Dawn on course for a close flyby of Mars on Feb. 4, 2009, that will alter the craft's trajectory, add a bit of velocity and put the probe on course to its first target - the asteroid Vesta.

If all goes well, says Harwood, Dawn will brake into orbit around the second largest asteroid on Aug. 14, 2011. After nine months of orbital exploration at varying altitudes, Dawn will move out of orbit and head off on a three-year voyage to the dwarf planet Ceres, the largest asteroid and the first ever discovered, arriving on Feb. 1, 2015.

Dawn is "the first mission to journey into and explore the heart of our asteroid belt," said Jim Adams, deputy director of planetary science at NASA headquarters. "It'll be the first to journey to and orbit around two celestial bodies and it'll be the first to visit a dwarf planet."

Ceres, Pluto and the recently discovered Eris in the extreme outer solar system are the only currently known members of the dwarf planet family, a new designation that emerged from the recent debate over how Pluto and other similar bodies should be classified.

"This is comparative planetology at its best," said Dawn program scientist David Lindstrom. "We are going to the two largest asteroids, but they are very different. Vesta is a very dense, igneous object from which we get plentiful meteorites. About 5 percent of the meteorites that fall on Earth come from the asteroid Vesta.

"We know that some of these rocks are (lava-like) basalts that crystallized 4.5 or (4.6) billion years ago, within a few million years of the earliest dated materials in the solar system. So we truly are going back in time, back to the dawn of the solar system.

"In contrast, Ceres, which is the largest asteroid and makes up about a quarter of the total mass in the asteroid belt, has much lower density indicating substantial amounts of ice. We have no known meteorites from Ceres so there's even more to learn by going to Ceres."

Dawn is the first operational deep space mission to be equipped with an ion propulsion system. Instead of burning liquid propellants in short, high-power bursts, Dawn's propulsion system works by using electrical power to ionize and accelerate electrically charged xenon to velocities 10 times greater than the exhaust from chemical rockets. One of Dawn's 12-inch-wide ion thrusters uses about 10 ounces of fuel over 24 hours of operation.

The resulting thrust is very low compared to chemical rockets, but it can be maintained for months at a time. Over the course of Dawn's mission, the ion engines will fire some 2,000 days, rivaling the capability of the entire Delta 2 rocket.

Dawn will get the necessary electrical power from two huge 27-foot-wide solar arrays that stretch 65 feet from tip to tip. The arrays are the most powerful ever sent into deep space, capable of generating 11,000 watts of power - enough for 10 average American homes.

Dawn doesn't need that much power, but the arrays were sized to provide sufficient energy when the spacecraft is orbiting Ceres, which is three times farther from the sun than Earth.

"This is NASA's first mission to use ion propulsion since it was proven on Deep Space 1 and it really is the key to why we can undertake such an ambitious and potentially rewarding journey in which we're going to be visiting some of the last unexplored worlds in the inner solar system," said Marc Rayman, Dawn project systems engineer. "The ion propulsion system is 10 times more efficient than conventional propulsion, so it allows us to undertake missions that are really far beyond the capability of conventional systems.

NASA originally hoped to launch Dawn in June, but the flight was delayed by a variety of booster-related issues, bad weather that interrupted launch processing and trouble with downrange tracking systems. NASA ultimately delayed the flight from July to September to avoid any possible conflict with launch of the Mars Phoenix lander in August.