Between the shuttle retirement and the launch of SpaceX's first cargo delivery flight in October 2012, NASA relied solely on spacecraft built by space agencies in Russia, Japan and Europe to send supplies to the station, but those vehicles aren't able to return cargo to Earth. Instead, the craft burn up in the planet's atmosphere.
Dragon, however, can bring cargo back to the ground to be studied or upgraded. This mission is slated to bring back about 2,300 lbs (1,043 kg) of space station material.
The 14.4-foot-tall (4.4 meters), 12-foot-wide (3.6 m) Dragon capsule is the first solar powered American spacecraft to dock with the International Space Station.
The space agency still relies on Russian Soyuz spacecraft to bring astronauts to the space station, but that could change eventually. NASA officials hope that a commercial firm, perhaps SpaceX or Orbital Sciences, will have the capability to send a manned mission to low-Earth orbit by 2017.
SpaceX's next launch to the space station is scheduled for fall of this year.