* Capsule to re-enter atmosphere and burn up on Wednesday
* NASA now has second U.S.-based supply line to station
* Firm preparing to fly next cargo ship in December
By Irene Klotz
CAPE CANAVERAL, Fla., Oct 22 (Reuters) - Virginia-based Orbital Sciences Corp completed a successful test mission at the International Space Station on Tuesday, clearing the firm to begin regular cargo runs for NASA under a $1.9 billion contract.
Using the space station's robotic arm, astronauts aboard the station plucked the Orbital Sciences' Cygnus capsule from its docking port and released the unmanned capsule into space as the two sailed high over the Atlantic Ocean.
The capsule was launched on Sept. 18 aboard an Orbital Sciences' Antares rocket from a new commercial spaceport on Wallops Island, Virginia.
Cygnus arrived at the station 11 days later. Docking was delayed a week due to a spacecraft communications glitch and the higher priority arrival of new station crew members aboard a Russian Soyuz capsule.
"This test flight went pretty much without any hiccups at all," NASA mission commentator Josh Byerly said during a NASA Television broadcast of Cygnus' departure.
The capsule is scheduled to make two braking maneuvers on Wednesday to lose altitude so it can be tugged back into Earth's atmosphere by the planet's gravity and burn up.
Cygnus, which carried about 1,300 pounds (590 kg) of cargo to the station, was loaded up with trash and items no longer needed aboard the station before its release.
Orbital Sciences is the second of two U.S. firms hired by NASA to fly cargo to the space station, a $100 billion project of 15 nations, following the retirement of the space shuttles in 2011.
Rival Space Exploration Technologies, or SpaceX, a privately owned California company, began work for NASA about 18 months before Orbital Sciences. It has already made a test flight and two cargo runs to the station, a permanently staffed research complex that flies about 250 miles (about 400 km) above Earth.
SpaceX, which is owned and operated by billionaire entrepreneur Elon Musk, has a $1.6 billion NASA contract for 12 station resupply missions, as well as a backlog of more than 40 other Falcon rocket flights for commercial satellite companies and non-U.S. government agencies.
"We are delighted to now have two American companies able to resupply the station," NASA administrator Charles Bolden said in a statement.
"Congratulations to the teams at Orbital Sciences and NASA who worked hard to make this demonstration mission to the International Space Station an overwhelming success," he said.
Like SpaceX, Orbital Sciences also hopes to sell its rockets to customers beyond NASA.
"With two really good launches under our belt, things are picking up in terms of customer interest," Orbital Sciences Chairman and Chief Executive David Thompson said during a conference call with investment analysts last week.
The company debuted its medium-lift Antares rocket during a test flight on April 21. Its next mission, scheduled for December, is the first of eight cargo runs to the station under a $1.9 billion contract with NASA.