Engineers at Cape Canaveral, Florida are making final preparations for another launch of the world's first privately-owned space cargo ship, on a mission to resupply the International Space Station.

Liftoff of the unmanned SpaceX Dragon cargo ship is set for 0135 hours UTC Sunday, with forecasters predicting a 60 percent chance of acceptable launch weather.

In May, an unmanned Dragon cargo ship supplied the space station in a test flight.

Sunday's mission is the first under a $1.6 billion contract between SpaceX — or Space Exploration Technologies Corp. — and NASA that calls for 12 resupply flights in the coming years.

The latest launch will see the Dragon tethered to the space station for most of October, as astronauts fill the capsule with blood and urine samples and other experiments for the return flight.

The samples have been stored in space station freezers since the last space shuttle flight in July 2011. The entire U.S. shuttle fleet was subsequently retired.

Unlike SpaceX, previous cargo supply ships flown by Russia, Europe and Japan burn up on reentry into the Earth's atmosphere, while the SpaceX Dragon is designed to parachute into the Pacific.

SpaceX is owned by Internet entrepreneur Elon Musk, who says he plans to fly humans to the space station by 2015.