Elon Musk's SpaceX keeps on completing milestones on its way to building that city on Mars ASAP, but first it must prove it can handle reliably traveling to somewhere much closer: the International Space Station, currently orbiting Earth. The Dragon is SpaceX's flagship space craft, and it has just completed its 4th successful mission resupplying the ISS, and the company has 8 more to go on its 12 mission contract with NASA.

The Dragon splashed down this past weekend in the Pacific Ocean after its four-week mission to the ISS at a location approximately 300 miles off the coast of Baja California. The space craft didn't just resupply the space station, it also brought back crucial information and data from experiments conducted aboard the ISS.

After being taken to Los Angeles, the Dragon will then have it's most important cargo removed there before having the rest of its contents harvested once it returns to SpaceX headquarters in McGregor, Texas. SpaceX and other private companies have contracted with NASA to ferry precious cargo to and from the ISS since the space shuttle program was retired in 2011.

SpaceX Dragon Flight Animation

NASA's head of its ISS division, Sam Scimemi, said of the mission, "This mission enabled research critical to achieving NASA's goal of long-duration human spaceflight in deep space."

Another aspect of this most recent Dragon mission was to deliver a 3-D printer to the space station and a device called ISS-RapidScat which measures the winds over the Earth's ocean.

According to Scimemi: "The delivery of the ISS RapidScatterometer advances our understanding of Earth science, and the 3-D printer will enable a critical technology demonstration." All told, the Dragon ferried 255 experiments to the ISS during this mission.

SpaceX's next Dragon flight is scheduled to begin this December, and it will deliver crew members in addition to supplies and experimental components. Earlier this year, NASA announced it was entering into a joint contract with Boeing and SpaceX to deliver astronauts and supplies to the ISS; the contract is worth $6.8 billion.

The first of these new manned flights by Boeing and SpaceX are expected to begin in 2017 after a rigorous testing and certification phase for the new spacecraft expected to shuttle crew and goods into orbit.