Commercial spacecraft firm Orbital Sciences Corp. says it will attempt to launch an unmanned cargo craft to the International Space Station after severe weather halted a first scheduled launch attempt.
The Cygnus robotic spacecraft was scheduled to launch into orbit atop one of the company's Antares rockets from NASA's Wallops Flight Facility in Virginia Saturday afternoon, but thunderstorm activity convinced company engineers to reschedule the attempt for Sunday.
Bad weather at the Wallops Island seaside launch complex is just the latest delay in Orbital's second unmanned supply mission to the space station; a first attempt to launch the Orb-2 mission in June was put off after an engine in the Antares launch vehicle malfunctioned while undergoing a ground systems test.
Orb-2 will ferry 3,300 pounds of supplies to the orbiting station, including tools, food, and science experiments to be conducted by the Expedition 40 crewmembers aboard the ISS.
The trouble-plagued mission is in stark contrast to Orbital Science Corp.'s inaugural Cygnus mission, which went without a hitch in January, conveying 2,800 pounds of supplies to the space station.
The company, based in Dulles, Va., was awarded a $1.9 billion contract by NASA calling for a total of eight of the cargo-resupply runs to the orbiting ISS.
Orbital Science Corp. and Space Explorations Technologies (SpaceX) are the only two commercial firms NASA has approved to conduct cargo missions to the space station.
SpaceX's $1.6 billion contract calls for 12 resupply missions, of which is has already completed three using its Falcon 9 rockets and Dragon spacecraft.
If Sunday's launch is successful -- local weather forecasts for the Wallops Island vicinity are predicting a 90 percent chance of clear skies -- the Cygnus craft will rendezvous with the ISS Tuesday morning, after which astronauts aboard the station will use a giant robot grapple arm to latch on to the cylindrical spacecraft.
German astronaut Alexancer Gerst has been practicing with the grapple in preparation for the capsule capture.
"A big moment in an astro's life: after 100s of sims, moving the real #ISS robotic arm for the 1st time. Felt great!" Gerst wrote in a tweet.
The Cygnus spacecraft will remain bound to the ISS for 30 days, during which time it will be filled with trash before being turned lose to return toward Earth and a fiery end in our planet's atmosphere.
Sunday's launch sequence at 12.52 pm EDT "will last about ten minutes from liftoff through the separation of Cygnus from the Antares Vehicle," Orbital Science Corp. said on its website.
