-- Data from Latest Test of AJ26 Engine Confirms High-Thrust Performance, Thrust Vector Control System Functioning, and Test Facility Operations --

DULLES, Va., Dec 20, 2010 (BUSINESS WIRE) --

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(R)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(R), 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.

In addition to its work with NASA on the COTS and CRS programs, Orbital is also offering the Taurus II rocket to U.S. civil government, military and commercial customers for dedicated launch services for medium-class satellites. From its Wallops Island, Virginia launch site, Taurus II will be capable of supporting mid-inclination and polar orbiting spacecraft weighing approximately 10,500 lbs. and 5,500 lbs, respectively. Development of a West Coast launch capability is planned for the future to optimize performance to high-inclination orbits.

About Orbital

Orbital develops and manufactures small- and medium-class rockets and space systems for commercial, military and civil government customers. The company's primary products are satellites and launch vehicles, including low-Earth orbit, geosynchronous-Earth orbit and planetary exploration spacecraft for communications, remote sensing, scientific and defense missions; human-rated space systems for Earth-orbit, lunar and other missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense systems that are used as interceptor and target vehicles. Orbital also provides satellite subsystems and space-related technical services to U.S. Government agencies and laboratories.

More information about Orbital can be found at http://www.orbital.com

Note to Editors: Photos of the AJ26 test can be found at: http://www.orbital.com/NewsInfo/ImagesMultimedia/Images/SpaceLaunch/index.shtml

SOURCE: Orbital Sciences Corporation

Orbital Sciences Corporation
Barron Beneski, 703-406-5528
Public and Investor Relations