Space Exploration Technologies' Dragon cargo ship started heading back to Earth from International Space Station (ISS) on Thursday after the first test flight.

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Dragon became the first privately owned vehicle to reach the $100 billion research complex, a project of 15 countries, on Friday when astronauts used the station's robot arm to pluck it from the orbit and latch it onto a berthing port as the spacecraft sailed about 250 miles above the planet.

The bell-shaped capsule, which was partly financed by NASA, was detached from the station at 4:07 a.m. EDT (0807 GMT) on Thursday and is to be released from the station's crane about 90 minutes later. Splashdown in the Pacific Ocean about 560 miles southwest of Los Angeles is expected at 11:44 a.m. EDT (1544 GMT).

Space Exploration Technologies, or SpaceX, successfully recovered a Dragon capsule from orbit during a previous test flight in December 2010.

We've done it once, but it's still a very challenging phase of flight, SpaceX mission director John Couluris told reporters on Wednesday.

The United States has been without its own transportation to the station since the space shuttles were retired last year. Rather than building and operating a government-owned replacement, NASA is investing in companies such as SpaceX with the intention of buying rides for its cargo - and eventually astronauts - on commercial vehicles, a far cheaper alternative.

The ability to get to (the) space station on our first time, to not only rendezvous but then to berth, transfer cargo and depart safely are major mission objectives. We would call that mission alone a success, Couluris said.

The successful trial run is expected to clear SpaceX to begin working off its 12-flight, $1.6 billion NASA contract to fly cargo to the station.

A second commercial freighter, built by Orbital Sciences Corp is expected to debut this year.

Our plans are to carry out a test launch in the August-September time frame and the demonstration mission - same as what SpaceX impressively just did - in the November-December time frame, Orbital spokesman Barry Beneski wrote in an email to Reuters.

Orbital has a similar contract to deliver space station cargo, valued at $1.9 billion.

After leaving the space station, SpaceX's Dragon capsule will fire its steering jets to leave orbit and begin its plunge through the atmosphere.

Recovery ships owned by American Marine Corp of Los Angeles will stand by to pick up the capsule and bring it back to the Port of Los Angeles, a trip that should take two to three days.

From there, Dragon will be taken to a SpaceX processing facility in McGregor, Texas, and unloaded and inspected.

The company's last test will be seen if it can speedily return some equipment coming back from the station to NASA within 48 hours, a practice run for ferrying home precious science samples when Dragon begins regular cargo hauls.

The rest of the 1,300 lbs (600 kg) of gear returning on Dragon is due to be sent to NASA within two weeks, said flight director Holly Ridings.

Because this is a test flight, specifically the program made sure that there's not anything coming home that we couldn't afford to not get back, she said.

I know it's a really important capability to prove for NASA and for the space station program as we go forward, since this vehicle has the unique capability to return cargo, she added.

The only vehicles that return to Earth are Russian Soyuz spacecraft, which primarily are used to transport crew and have little room for cargo. The other freighters are discarded and burnt up in the atmosphere.

NASA Los Angeles International Space Station Spacex