(Reuters) - A SpaceX Falcon Heavy rocket blasted off from Kennedy Space Center in Florida on Tuesday, putting 24 experimental satellites into orbit after what Elon Musk’s rocket company called one of its “most difficult” launches ever.

The craft lifted off to cheers from onlookers at 2:30 a.m. (0630 GMT) after a three-hour delay from the original launch time late Monday.

The boosters separated safely as the craft began its six-hour mission to deploy the satellites.

The two side booster rockets returned safely to Earth, descending onto adjacent Air Force landing pads, but the rocket’s center booster missed its mark, crashing in the Atlantic Ocean.

Musk, who predicted trouble landing the center booster on SpaceX’s drone ship, said on Twitter early Tuesday, “It was a long shot.”

The mission, dubbed Space Test Program 2 (STP-2), is the third for the Falcon Heavy rocket, which SpaceX describes as the most powerful launch system in the world.

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REUSABLE ROCKET

It was commissioned by the U.S. Department of Defense, the key contractor for commercial space companies such as SpaceX.

SpaceX has landed and used many of its booster rockets more than once, touting their reusability as an effective way to cut the costs of future space travel.

The U.S. Space and Missile Systems Center, a unit of the U.S. Air Force, said all the satellites lifted into orbit had been deployed and made contact after what one of its officials called “a momentous launch.” It marked the first time that the Pentagon has allowed its satellites or other hardware to be launched aboard a previously used rocket.

“The SpaceX Falcon Heavy allows the Air Force to begin using previously flown rocket technology to further reduce the cost of launch,“ said Colonel Dennis Bythewood, program executive officer at the Space and Missile Systems Center in Los Angeles.

The company deployed the satellites for agencies including NASA and the National Oceanic and Atmospheric Administration (NOAA), defense department laboratories, universities and a non-profit organization, SpaceX said.

The mission was one of the most challenging in SpaceX history, with four separate upper-stage engine burns and three separate orbits to deploy the satellites, the company said on its website.

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SOLAR SAIL

The payloads on the satellites Falcon Heavy put into orbit included an atomic clock NASA is testing for space navigation, another testing new telescope technologies, and a solar sail project part-funded by the Planetary Society, a non-profit organization headed by Bill Nye, popularly known as the “Science Guy” from his frequent U.S. TV appearances.

The LightSail 2 is a crowdfunded project that aims to become the first spacecraft in Earth orbit propelled solely by sunlight, the Planetary Society, which has championed solar propulsion for decades, said on its website.

LightSail 2 was enclosed within Prox-1, a small satellite built by Georgia Tech students, which will deploy it on July 2, according to the website.

Falcon Heavy is the most powerful operational rocket in the world “by a factor of two,” SpaceX said on its website. It has the ability to lift nearly 64 metric tons (141,000 pounds) into orbit - more than a 737 jetliner loaded with passengers, crew, luggage and fuel.