SpaceX's "reusable" rocket crashes into its floating landing pad in the Atlantic Ocean

SpaceX's Falcon 9 rocket lifts off early Saturday from Cape Canaveral Air Force Station in Florida. An attempt to land the rocket on a platform in the Atlantic Ocean was unsuccessful.NASA

SpaceX almost made history on Saturday. Almost.

As part of its NASA-contracted mission to resupply the International Space Station, the private space-exploration company was attempting to launch the "world's first reusable rocket" and then land it on a landing pad floating in the Atlantic Ocean.

The launch, which was scrapped earlier this week because of a problem with a rocket part, went off without a hitch at 4:47 a.m. local time at Cape Canaveral Air Force Station in Florida, according to NASA.

SpaceX's 14-story Falcon 9 rocket also successfully sent a Dragon cargo capsule on its way to the space station. But when the first stage of the Falcon 9 returned to Earth, it crashed into its 300-by-100-foot floating landing pad.

"Close, but no cigar this time," SpaceX CEO Elon Musk tweeted Saturday morning. "Bodes well for the future tho."

SpaceX is one of a handful of private companies pursuing spaceflight, a realm once solely controlled by government space agencies. But the task isn't easy. In August, a SpaceX Falcon 9 rocket explodedduring a test flight. And in October, space-tourism company Virgin Galactic saw one of its space planescrash during a test flight, a mishap that killed one of the plane's two pilots.

Before Saturday's launch, SpaceX had put the odds of a successful landing at 50 percent "at best" and likened hitting the bull's eye to "trying to balance a rubber broomstick on your hand in the middle of a wind storm."

SpaceX has already started assessing what went wrong, and Musk tweeted an initial finding: "Grid fins worked extremely well from hypersonic velocity to subsonic, but ran out of hydraulic fluid right before landing." The grid fins are an upgrade for the rocket and are designed to move independently to help with landing, according to SpaceX.

Here are two of the four grid fins on SpaceX's Falcon 9 rocket. An issue with them may have contributed to the crash landing.SpaceX

Saturday's launch was part of SpaceX's fifth resupply mission to the International Space Station. The cargo on the Dragon capsule included two tons of gear, supplies, experiments and food, NASA said. The Dragon is scheduled to reach the space station on Monday.

SpaceX has seven more supply missions to go as part of a $1.6 billion contract with NASA.

In two test flights last year, SpaceX proved that Falcon 9 rockets can slow themselves down and use landing gear. In both those tests, though, the rocket tipped into the ocean after touching down.

According to SpaceX, reusable rockets are the key to reducing the cost of space missions and travel. "The majority of the launch cost comes from building the rocket, which flies only once," according to the company's website.