By Irene Klotz
WASHINGTON, Jan 9 (Reuters) - An unmanned Orbital Sciences Corp. Antares rocket blasted off on Thursday bound for the International Space Station to deliver the first of eight cargo ships for NASA.
The 13-story rocket lifted off its seaside launch pad in Wallops Island, Virginia, at 1:07 p.m. EST/1807 GMT, putting the Cygnus freighter on track for an early Sunday rendezvous with the station.
Launch, which was broadcast live on NASA Television, was delayed twice this week, first by cold weather and then by high space radiation stemming from a massive solar flare on Tuesday. Both conditions could have impacted critical rocket systems.
Orbital Sciences is one of two firms hired by NASA to fly cargo to the station, a $100 billion project of 15 nations, following the retirement of the space shuttles in 2011.
Privately owned Space Exploration Technologies, or SpaceX, is preparing for its third supply run on Feb. 22 from Cape Canaveral Air Force Station in Florida.
Thursday's launch was the third for Antares, a medium-lift rocket that Orbital also is marketing for satellite launches.
"We are negotiating with people with other payloads besides the Cygnus spacecraft and intend to fly more cargo out of Wallops," Orbital Sciences executive vice president Frank Culbertson told reporters during a prelaunch news conference on Tuesday. He declined to elaborate on prospective customers.
The company holds a $1.9 billion contract with NASA to fly eight Cygnus cargo ships to the station, a permanently staffed research outpost that flies about 250 miles (about 400 km) above Earth.
SpaceX has a separate 12-flight NASA contract worth $1.6 billion.
Orbital Sciences and SpaceX previously received a combined $686 million from NASA to help develop their rockets, capsules and launch sites.
Orbital Sciences' Antares rockets fly from a commercial space port carved out of NASA's Wallops Flight Facility in Virginia. SpaceX's NASA missions launch from Cape Canaveral Air Force Station in Florida.
Orbital Sciences debuted its Antares rocket in April 2013 and made a successful test run to the space station five months later. It planned to start flying cargo in December, but NASA delayed the flight to tackle a high-priority repair to the station's cooling system.
Cygnus is loaded with 3,221 pounds (1461 kg) of equipment and supplies for the station, including science experiments, computers and replacement parts for NASA's spacesuits.
The capsule also holds food, fresh fruit and belated Christmas gifts for the crew. "We haven't changed them out for Valentine's cards," Culbertson quipped.
The freighter is due to arrive at the station shortly after 6 a.m. EST/1100 GMT on Sunday.