WASHINGTON, May 21 -- A commercial cargo ship, operated by private U.S. space firm SpaceX, left the International Space Station on Thursday morning, concluding its sixth contracted commercial resupply mission to the orbital laboratory.

After a one-month visit, the Dragon capsule was detached and released at 7:04 a.m. EDT (1104 GMT) from the Earth-facing side of the station's Harmony module using a robotic arm, operated by ground controllers at the U.S. space agency NASA's Johnson Space Center in Houston.

The capsule was expected to splash down in the Pacific Ocean at 12:42 p.m. EDT (1642 GMT), about 250 km southwest of Long Beach, California, said NASA.

Dragon, the only space station resupply spacecraft able to return to Earth intact, was launched on April 14 on a SpaceX Falcon 9 rocket from the Cape Canaveral Air Force Station in Florida, and arrived at the space station three days later.

It delivered more than 2 tons of supplies and research equipment, including a coffee machine, to the station.

Dragon's seventh cargo mission is scheduled for June 26.