SpaceX's effort to attach itself to NASA's International Space Station operations took a big step forward on Monday when the Elon Musk-backed company's Cargo Dragon capsule docked at the ISS.

It's the first time SpaceX has ever had two spacecraft docked to the ISS simultaneously, and should be the start of a near-permanent presence for SpaceX at the space station.

SpaceX Falcon 9 rocket lifting off from Kennedy Space Center in Florida

SpaceX's Falcon 9 rocket lifts off from Kennedy Space Center in Florida on Dec. 6, 2020. Image source: Kim Shiflett, NASA.

The latest capsule launched Sunday from NASA's Kennedy Space Center in Florida, and is the first launch for SpaceX under a NASA commercial resupply contract to deliver suppliers, equipment, and materials to the ISS. Cargo Dragon will join SpaceX's Crew Dragon, which has been docked at the ISS since bringing four astronauts to the ISS in November.

SpaceX is building additional Dragon capsules to cater to NASA's crew and cargo needs, with a steady stream of capsules expected to shuttle between Earth and the station in the years to come.

SpaceX and Boeing (NYSE:BA) each have contracts with NASA to service the ISS, but so far SpaceX has been first to deliver. Boeing's competing Starliner spacecraft has had some development issues, and does not expect to do its next test launch until the first quarter of next year.

For SpaceX, the revenue that comes with these NASA launches is a key part of its effort to fund research and development into its other extraterrestrial ambitions, most notably Musk's hope of one day colonizing Mars.

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