Orbital Sciences Corporation (NYSE: ORB), one of the world’s leading space technology companies, today announced that it successfully carried out a long-duration test firing of the liquid-fueled AJ26 rocket engine that will power the first stage of the company’s Taurus ®II space launch vehicle. In a test conducted on Friday, December 17 at NASA’s Stennis Space Center in Mississippi, Orbital and its engine supplier Aerojet, a unit of GenCorp (NYSE: GY), oversaw a test of the AJ26 engine at the recently refurbished E-1 test stand. The AJ26 engine test ran for 55 seconds, during which the engine was purposely stressed to 109% (or about 370,000 lbs) of its baseline thrust level. The test of the engine’s primary control functions accomplished all primary objectives, including engine startup, propellant valve commanding, thrust vector control functioning and shutdown sequencing. Preliminary review of the test data indicated that all test objectives were met. The data collected from Friday’s test will be used to fine-tune the AJ26 engine system and prepare it for a third and final firing in mid-January, which will verify tuning of engine control valves. The first stage of the Taurus II launch vehicle is powered by two liquid oxygen/kerosene AJ26 engines, which together generate nearly 740,000 lbs. of liftoff thrust and accelerate the vehicle to a speed of 10,700 miles per hour in the first 235 seconds of flight. As the Taurus II program enters its initial launch phase in 2011, each AJ26 engine will be subjected to rigorous acceptance testing at Stennis prior to being shipped to the Taurus II integration site at NASA’s Wallops Flight Facility in Eastern Virginia. Three more AJ26’s are scheduled for testing over the next five months. About Taurus II Orbital is developing the Taurus II medium-class space launch vehicle to boost payloads into a variety of low Earth and geosynchronous transfer orbits and Earth escape trajectories. Taurus II incorporates proven technologies from the company’s Pegasus ®, Taurus and Minotaur rockets, and is supported by a “best-in-class” network of suppliers from the U.S. and around the world. The Taurus II program currently has a backlog of nine launches, beginning with the Commercial Orbital Transportation Services (COTS) project, a joint research and development effort with NASA to develop a space transportation system capable of safely and reliably supplying the International Space Station (ISS) with essential cargo. Orbital is also under contract with NASA for the Commercial Resupply Services (CRS) program with an eight-mission, $1.9 billion agreement to deliver cargo to the ISS from 2011 through 2015.