SpaceX's robotic Dragon capsule is slated to blast off Sunday night (Oct. 7) on the first-ever bona fide private cargo run to the International Space Station.

In May, Dragon become the first commercial spacecraft to visit the station. But that was a demonstration flight, while Sunday's launch kicks off the first of 12 unmanned supply missions SpaceX will make for NASA under a $1.6 billion contract.

Dragon will deliver about 1,000 pounds (454 kilograms) of supplies, then return to Earth on Oct. 28 carrying more than 1,200 pounds (544 kg) of different gear down from the space station. Here's how the mission will work.

Getting into space

The Dragon capsule is set to blast off atop SpaceX's Falcon 9 rocket at 8:35 p.m. EDT Sunday (0035 GMT Monday). The mission has an instantaneous launch window, so if anything causes a delay Sunday, liftoff will be pushed to another day.

At about 1 p.m. EDT Sunday (1700 GMT), Dragon and the Falcon 9 will be powered up, and fueling of the rocket will begin three and a half hours later. [SpaceX's Dragon Poised to Launch Sunday (Photos)]

The terminal countdown begins at T-minus 10 minutes and 30 seconds, at which point all launch systems will be autonomous. A final "go" for launch will come at T-minus 2 minutes and 30 seconds, NASA officials said.

Seventy seconds after liftoff, the Falcon 9 rocket will reach supersonic speed. By 2.5 minutes into the flight, it will be traveling 10 times the speed of sound, at an altitude of 56 miles (90 kilometers). At about this time, the rocket's main engines will cut off.

A few seconds later, the Falcon 9 rocket's first and second stages will separate, with the second stage soon performing a six-minute burn to take Dragon to low-Earth orbit.

Nine minutes and 49 seconds after launch, Dragon will separate from the rocket's second stage. Seconds later, the capsule will reach its preliminary orbit, at which point it will deploy its solar arrays and begin a series of thruster firings to get it close to the space station.

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How SpaceX's First Space Station Cargo Mission Will Work