Space Exploration Technologies' Dragon spaceship is poised to wrap up a pioneering test flight, the first by a private company to the International Space Station, and head back to Earth.
Dragon became the first privately owned vehicle to reach the $100 billion (€80 billion) research complex, a project of 15 countries, last week when astronauts used the station's robot arm to pluck it from orbit and latch it onto a berthing port as the spacecraft sailed about 402 km above the planet.
The bell-shaped capsule, which was partly financed by NASA, was scheduled to be detached from the station 8am (Irish time) and released from the station's crane about 90 minutes later.
Splashdown in the Pacific Ocean about 907 km southwest of Los Angeles is expected at 3.44pm.
Space Exploration Technologies, or SpaceX, successful 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 last night.
The United States has been without its own transportation to the station since the space shuttles were retired last year.
Rather than build and operate 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," Mr 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 said.
Orbital has a similar contract to deliver space station cargo, valued at $1.9 billion. After leaving the space station, SpaceX's Dragon capsule is expected to 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 be standing by to pick up the capsule and bring it back to the Port of Los Angeles, a trip that should take two or 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 to see 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.
Reuters