SpaceX had originally slated the launch for Dec. 19, but after the rocket's Merlin 1D engines failed to run for the full three seconds during a static fire test on Dec. 17, the company rescheduled for early 2015.

A second test on December 19 was successful, clearing the rocket for launch in January, which will end with a test of the rocket attempting to land upright on an open-ocean platform — a big hurdle to making reusable rockets. Elon Musk said that the attempt has about a 50% chance of success.

Reusable Rockets

The Jan. 6 launch will ferry 3,700 pounds of science experiments, spare parts, food, water, and other supplies to the International Space Station on the Dragon spacecraft.

But the most important part of the launch will not be what goes up, but what comes down. After the Falcon 9 rocket has emptied most of its fuel, it will detach from the Dragon spacecraft. That's when things get interesting as the rocket, using GPS tracking, navigates its way down onto a floating platform in the Atlantic Ocean. But it won't be easy.

"During previous attempts, we could only expect a landing accuracy of within 10 kilometers (6.2 miles). For this attempt, we're targeting a landing accuracy of within 10 meters (33 feet)," SpaceX said in a statement.