It was SpaceX's second attempt to land the first stage of its Falcon 9 rocket on the floating platform, which Musk calls an "autonomous spaceport droneship," essentially a modified barge that’s 300 feet long by 170 feet wide.
In January, the rocket crashed and exploded into a spectacular fireball. Another recent attempt was scratched because of high seas.
Typically, rocket boosters are used once, burning up or crashing into the ocean after liftoff. But Musk, the billionaire co-founder of PayPal and Tesla, has been working on creating reusable rockets that act like airplanes—fly, land, then fly again. If SpaceX, his Los Angeles-based company, can repeatedly land rockets and reuse them, it would mark a significant step toward making spaceflight much more affordable.
Tuesday's attempt came after years of development and testing. SpaceX had been successful at launching rockets a few hundred feet into the air, and then bringing them back down to the landing pad. In previous launches, it brought rockets down to Earth, where they hovered over the ocean for a few seconds before crashing.
The ability to consistently land and reuse rockets, one of space flight’s holy grails, is part of Musk’s plan to further explore the cosmos and eventually colonize Mars.
As he said during a forum at MIT last year, there are "no runways on Mars," meaning rockets would have to land using the thrust in their engines.
A successful landing would be yet another breakthrough for SpaceX. It was the first commercial company hired by NASA to ferry supplies to the International Space Station. And it won another contract, along with Boeing, to fly astronauts to the station, starting as soon as 2017.
But as SpaceX has evolved from spunky start-up to a mainstream space company, Musk has continued to push toward developing the technologies that eventually would make humans an "interplanetary species."
In order to do that, the cost of space flight, now prohibitively high, would have to come down dramatically. And the ability to reuse rockets — as commercial airlines repeatedly reuse their aircraft — ultimately will make space travel more accessible, Musk has said.
"Imagine if aircraft were single use — how many people would fly?" he said at the MIT forum. "Nobody’s paying half a billion dollars to fly from Boston to London."
Once it docks with the space station later this week, SpaceX’s Dragon capsule will unload some 4,300 pounds of cargo, including science experiments, food, and even an espresso maker.
It is also carrying material that could be used as synthetic muscles in robots and prosthetics. The material "contracts with an electric current and expands back to its original state when the charge is reversed," according to NASA. The astronauts will test the material to see how it functions on the station to determine if they could be used on robots in space.
Among the astronauts on board is Scott Kelly, who recently began a year-long tour on the station. Scientists will study how so much time in orbit affects the human body, research that could help prepare astronauts to fly on deep-space missions.