Just before 4:00 a.m. this morning, the SpaceX Falcon 9 rocket successfully lifted off from Cape Canaveral, carrying the first privately built spacecraft to visit the International Space Station. The unmanned mission will resupply the ISS and, if successful, could be the first step to replacing America's Space Shuttle program with private vehicles.

SpaceX, a private company founded by former PayPal CEO Elon Musk,  has a $1.6 billion contract with NASA to become the future supplier of cargo to the ISS and eventually (if all goes well) people. The space agency — which is still responsible for the launch and mission control — also provided about half of the company's seed money to help develop the Falcon rockets and the Dragon capsule that sat on top of it and is now in orbit. Since retiring the Space Shuttle program last year, the United States has no way to get astronauts and equipment into space and must rely on the Russian space program, who it must pay around $63 million per astronaut to get a ride to ISS. Another company, Orbital Sciences Corporation, is also working with NASA on its own supply ships.

The Dragon capsule will rendezvous with the ISS on May 25 to drop off supplies and then return to Earth, dropping into the Pacific Ocean, where it will (hopefully) be recovered and used again on a future mission.