SpaceX's Falcon Heavy, the world's most powerful rocket, thundered to life and shot away from Florida Tuesday on the power of 27 engines and nearly 5 million pounds of thrust, kicking off a spectacular maiden flight to send founder Elon Musk's cherry red Tesla Roadster on a "just for fun" journey beyond the orbit of Mars.

It was easily the loudest and possibly most dramatic launch from Florida's "Space Coast" since NASA's space shuttle was retired in 2011 with the Falcon Heavy, made up of three strapped-together core stages powered by nine engines each, putting on a dazzling show for tourists and area residents jamming nearby roads and beaches.

Spectacular as it was, the launching was just the appetizer for a long-awaited test flight. Eight minutes after the rocket took off, two of the three Falcon 9 core stages that helped power the vehicle out of the lower atmosphere made rocket-powered descents to side-by-side touchdowns at the Cape Canaveral Air Force Station, generating thunderous sonic booms as they slowed for landing.

Recovering rocket stages was impressive in its own right, but it was a secondary test objective. The primary goal was to prove the rocket's ability to boost heavy payloads into space.

While the Tesla on board for the rocket's first test flight tipped the scales at a relatively modest one ton or thereabouts, the Heavy has the ability to boost nearly 140,000 pounds to low-Earth orbit and more than 37,000 pounds to Earth-escape trajectories to Mars.

NASA is currently building an even more powerful rocket known as the Space Launch System, or SLS, that will generate 8.8 million pounds of thrust in its initial configuration and up to 11.9 million pounds in a follow-on cargo variant. The initial version will be able to boost more than 50,000 pounds to Earth-escape velocity.

But the SLS is not expected to fly until late 2019 or later. Until then, the Falcon Heavy will be the world's most powerful rocket, offering a relatively low-cost option for getting heavy payloads into space for NASA, the Department of Defense and commercial satellite operators.

U.S. Commerce Secretary Wilbur Ross, who attended the launch at the Kennedy Space Center, said the Heavy offers a promising alternative for heavy weight national security satellites that are too big for the Falcon 9 and currently fly exclusively on more expensive United Launch Alliance Delta 4s.

"The national security people have indicated that assuming this test or a subsequent one goes well they would plan to use this Falcon Heavy for classified missions," he said.

The rocket also could be used to launch astronauts or space tourists to the moon, although plans for such flights are not yet mature.

Made up of three strapped-together Falcon 9 first stages and a single upper stage, carrying the Tesla, the Falcon Heavy's engines flashed to life at 3:45 p.m. EST (GMT-5), two hours and 15 minutes late because of higher-than-allowable upper-level winds.

After a lightning-fast round of computer checks, the 229-foot-tall rocket was released to climb away from from the pad, shattering the afternoon calm with an ear-splitting roar and an impossible-to-miss rush of fire from all 27 engines, nine at the base of each core stage.

The business end of the Falcon Heavy: 27 Merlin engines, clustered in groups of nine, developing nearly 5 million pounds of thrust at liftoff. / SpaceX

Going into the flight, Musk predicted a 50 percent to 70 percent chance of success based in large part on the difficulty predicting how the vehicle would respond to extreme aerodynamic stresses and vibrations from the clustered engines.

As it accelerated skyward, aerodynamic forces quickly ramped up, forming an invisible "bow shock" over the nose of the central core stage, creating complex interactions and, possibly, localized heating as the spacecraft picked up speed plowing through the thick lower atmosphere.

But the Heavy endured those stresses, rocketing through the speed of sound and the region of maximum aerodynamic stress about a minute after liftoff.

The 18 engines in the two outboard core stages shut down two-and-a-half minutes after launch. Both stages then separated from the core booster, flipped around, restarted three engines each and began flying back to Florida.

The nine center stage engines continued firing for another 30 seconds or so before they, too, shut down and the second stage pulled away on its own, lighting up a single Merlin engine to continue the boost toward a preliminary orbit.

The central core stage then fired three of its engines to set up a landing on an off-shore drone ship stationed several hundred miles east of Cape Canaveral. The two outboard stages, meanwhile, restarted three engines to slow down for atmospheric entry.

The burns -- brilliant side-by-side jets of flame -- were clearly visible across Florida's east coast as the boosters plunged tail-first toward pads at Landing Zone 1 at the Cape Canaveral Air Force Station. Falling like bombs, the rockets each restarted a single engine to slow for touchdown, each one deploying four landing legs.

A shot of the Falcon Heavy atop pad 39A at the Kennedy Space Center during pre-flight tests last month. / SpaceX

Heralded by dual sonic booms that thundered across Cape Canaveral, both boosters touched down about eight minutes after liftoff. The central core landed on SpaceX's off-shore drone ship about 20 seconds later.

A few moments after that, the second stage engine shut down putting the rocket and Musk's still-attached Tesla Roadster into a preliminary orbit. A second engine firing 20 minutes later was planned to adjust the orbit as required to set up a trajectory to Mars.

A third rocket firing was planned about six hours later to boost the spacecraft's velocity to nearly 25,000 mph, fast enough to escape the pull of Earth's gravity. Again, Musk downplayed expectations.

"Once we reach orbit, we've got a very long coast, we've got a six-hour coast before restart, which is twice as long as we've ever coasted a stage," he said. "So we could see the fuel potentially freeze, because it's out there in deep space and when it's not facing the sun it's at three degrees above absolute zero.

"So it could easily freeze, or the liquid oxygen could boil off, so there's a lot that could go wrong."

Assuming it makes it through the high-radiation environment of Earth's Van Allen belts, and assuming the Falcon Heavy's second stage propellant doesn't freeze or boil away, the flight plan called for the Tesla to be released on a trajectory carrying it slightly farther than the orbit of Mars.

A mannequin known as Starman, wearing a spacesuit, was strapped into the driver's seat, its left arm casually draped across the door as if cruising through the country side. Or a long flight to Mars.

SpaceX founder Elon Musk's cherry red Tesla Roadster sports car, with a space-suited dummy pilot "Starman," will serve as a test payload for the Falcon Heavy in its maiden flight. / SpaceX

"We expect it'll get about 400 million kilometers away from Earth, maybe 250 to 270 million miles, and be doing 11 kilometers per second," Musk said. "It's going to be in a precessing elliptical orbit with one part of the ellipse being at Earth orbit and the other part being at Mars orbit. So it'll essentially be an Earth-Mars cycler.

"We estimate it'll be in that orbit for several hundred million years, maybe in excess of a billion years," he said. "At times, it will come extremely close to Mars, and there's a tiny, tiny chance that it will hit Mars (someday). Extremely tiny. I wouldn't hold your breath."

New rockets making their first flights typically carry dummy payloads, or "mass simulators." But not the Falcon Heavy.

"It's just for fun," Musk laughed in an interview. "A lot of people (wondered) what's the purpose of sending a car to Mars? There's no point, obviously! It's just for fun and to get the public excited."

Musk believes the Falcon Heavy, which at $90 million a copy costs much less than ULA's less-powerful rockets or the European Ariane 5 booster, is a potential game-changer for SpaceX. But first, the company must demonstrate the Heavy's reliability.

And it's not yet clear how the Falcon Heavy figures into SpaceX's long-term plans, whether enough customers, including NASA, will buy the Heavy for commercial satellite-launching missions, to send interplanetary probes into deep space or possibly to send space tourists into orbit aboard a piloted version of SpaceX's Dragon spacecraft.

"I think Heavy creates a lot of opportunities," said John Young, an engineer on a SpaceX advisory board. "There are several communities in Washington that would love to have a bigger aperture, either optical or radar, to collect more (national security) data, so this creates a whole new opportunity."

But it's unclear how SpaceX's efforts to develop an even larger rocket, known as the BRF, will affect its near-term plans for the Heavy. Musk said last year the Heavy would be used to launch two paying customers on a flight to loop around the moon by the end of this year, but that mission is on hold.

"The Falcon Heavy is definitely capable of sending the crewed Dragon vehicle around the moon," Musk said. "We may still do that, it depends on how quickly the BFR development goes. If that development's looking good, then we will try to push everything to BFR. If that's looking like it's going to take longer than expected, then we'll send people around the moon using Falcon Heavy and Dragon.""

But the BFR is the clear focus, a rocket system that he says will be "ideal for interplanetary colonization and for establishing a large base on the moon and a city on Mars. But this (the Falcon Heavy) is a prelude to that, this is going to teach us a lot about what's necessary to have a huge booster with a crazy number of engines."

For now, the Heavy remains a rocket under development. SpaceX's bread and butter comes from satellite launches using the Falcon 9 and it has a $10 billion manifest. SpaceX also holds NASA contacts valued at more than $2 billion for 20 space station resupply flights and a subsequent contract covering another six cargo missions.

The company is building a piloted version of its Dragon capsule to ferry astronauts to and from the station under a separate $2.6 billion contract and the company recently won a second long-term station resupply contract, with an unspecified value, for another half-dozen resupply missions.

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