KENNEDY SPACE CENTER, Fla.--A towering Atlas 5 rocket flashed to life and vaulted into space Saturday, putting on a spectacular weekend sky show as it boosted NASA's $2.5 billion Mars Science Laboratory rover on an eight-and-a-half-month, 352-million-mile voyage to the Red Planet.

Equipped with a nuclear power pack, a robot arm, and a suite of sophisticated instruments, the mobile laboratory, dubbed Curiosity in a student naming contest, is expected to spend at least two years looking for organic compounds and signs of past or present habitability in the layered terrain at the heart of a 100-mile-wide crater.

United Launch Alliance

It's the most complex and scientifically ambitious Mars mission yet attempted, one that promises to revolutionize humanity's understanding of martian history and whether the planet ever had--or still has--the raw materials and an environment hospitable to the evolution of life.

"We are ready to go for landing on the surface of Mars, and we couldn't be happier," Project Scientist John Grotzinger told reporters after the rover was safely on its way. "I just can't wait to get on the ground."

Doug McCuistion, director of the Mars Exploration Program at NASA headquarters in Washington, said he was "ecstatic."

"We have started a new era of exploration of Mars with this mission, not just technologically, but scientifically," he said. "I hope we have more work than the scientists can actually handle. Once we get to the surface, I expect them all to be overrun with data that they've never seen before."

And the public can expect dramatic new vistas from the floor of Gale Crater, Curiosity's landing site.

"Those first images are going to just be stunning, I believe," McCuistion said. "It's going to be like sitting at the bottom of the Grand Canyon. So we are absolutely ecstatic. Can't wait to get to Mars."

The long-awaited mission got under way on time at 10:02 a.m. ET, when the rover's United Launch Alliance Atlas 5 rocket roared to life and lifted away from launch complex 41 at the Cape Canaveral Air Force Station.

Equipped with four solid-fuel strap-on boosters for additional power, the 1.2-million-pound Atlas 5 blasted off with nearly 2 million pounds of thrust, majestically climbing away from its seaside pad and arcing toward the East through scattered clouds as it accelerated spaceward.

Trailing a churning cloud of fiery exhaust, the strap-on boosters were jettisoned just under 1 minute and 55 seconds into the flight, and the rocket continued on its way under the power of its Russian-built RD-180 first-stage engine.

Four-and-a-half minutes after takeoff, the first stage dropped away and the hydrogen-fueled RL10 engine at the base of the Centaur second stage ignited, powering the spacecraft toward a planned 102-by-201-mile-high parking orbit 11-and-a-half minutes after launch.

Telemetry from the rocket was spotty during a 20-minute coast to the Mars departure point, but the Centaur reignited as planned for a final 8-minute burn, accelerating the spacecraft to an Earth-escape velocity of 22,500 mph. A few moments after that, at 10:46 a.m., the Mars Science Laboratory and its solar-powered interplanetary cruise stage separated from the Centaur, completing the launch phase of the mission.

"Our spacecraft is in excellent health, and we're on our way to Mars," Project Manager Peter Theisinger told reporters. "We separated perfectly, on time, and the acquisition of signal was as expected, about six minutes later. We are power positive, slowly charging the batteries.... We are thermally as expected, the heaters for propulsion are on, the temperatures are as we expect them on the key pieces of equipment, and we're changing slowly as you'd expect as we transition from ground-based to space operations.

"We are in cruise mode," he concluded. "We have commanded the spacecraft and we are therefore in two-way (communications) and are getting navigation data. The injection was first rate.... That's about it from me. A very happy guy."

During the craft's 8-and-a-half-month cruise to Mars, engineers at the Jet Propulsion Laboratory in Pasadena, Calif., will test the rover's instruments, adjust the craft's trajectory, and tweak the control software that's vital to the mission's success.

If all goes well, Curiosity will reach the Red Planet on Aug. 5 for a nail-biting six-minute descent to the floor of Gale Crater.

Just before entry, the cruise stage will reorient the spacecraft, and small weights will be ejected to change the entry vehicle's center of gravity, providing the lift necessary for a guided descent.

Using an advanced heat shield to endure entry temperatures of up to 3,400-degrees Fahrenheit, the rover's flight computer will fire small rocket thrusters as required to fine-tune the craft's fight path based on actual atmospheric conditions.

Four minutes and 15 seconds after entry, at a velocity of about 900 mph and an altitude of roughly 7 miles, a huge braking parachute will unfurl, slowing the probe's plunge to a more manageable 180 mph. At that point, at an altitude of just under 1 mile, the rover and its "sky crane" rocket pack will fall free of the parachute assembly for a powered descent to the surface.

NASA

For JPL flight controllers monitoring the computer-controlled descent, this will be the moment of truth.

Too large to use airbags like those that cushioned NASA's Pathfinder, Spirit, and Opportunity rovers, Curiosity will rely instead on landing rockets positioned above the rover, avoiding the challenge of coming up with a reliable way to get a 1-ton vehicle off of an elevated, possibly tilted lander.

Using a high-precision radar altimeter, sophisticated attitude sensors, and complex software, Curiosity's radiation-hardened computer will control the dual rockets on each corner of the sky crane to achieve a steady 1.7 mph vertical descent rate.

Just before touchdown, the rover will be lowered from the hovering sky crane on a long tether, gently setting down on its six 20-inch-wide wheels. At that point, the bridle will be cut, the sky crane will fly away to a crash landing and flight controllers will begin checking out and activating Curiosity.

Thanks to the sky crane and the guided entry, mission planners were able to select the most scientifically interesting target--Gale Crater--from a list of carefully considered candidates.

Starting on the floor of the vast crater and then slowly ascending the central peak through canyons and ravines visible in orbital photography, "we're basically reading the history of Mars' environmental evolution," Grotzinger said before launch.

"We start at the bottom, where...the clays are, we go up farther, there are the sulfates, and then we go to the top of the mound and we get rocks that we think were formed...in the drier, more recent phase of Mars," he said.

Climbing the central peak with its exposed layers will be "analogous to what you would see in the Grand Canyon," Grotzinger said. "So our rover is going to be like John Wesley Powell going down the Grand Canyon on Mars, looking at this thick stack of strata."

The mission is expected to last at least two years and possibly longer if the rover stays healthy and no major malfunctions occur.

The primary goal of the mission is to determine if Mars ever had a habitable environment at some point in its history, areas where the three necessities of life--water, energy, and carbon compounds--existed in concert.

The first two are now well established, thanks to earlier Mars missions that showed Mars was once a much warmer, wetter world. But the search for carbon compounds is a much more challenging proposition.

"The promise of Mars Science Laboratory, assuming that all things behave nominally, is we can deliver to you a history of formerly, potentially habitable environments on Mars," Grotzinger said. "But the expectation that we're going to find organic carbon, that's the hope of Mars Science Laboratory. It's a long shot, but we're going to try."