-- Company's Long-Range, Silo-Launched Booster Completes Seventh Consecutive Successful Flight for the Ground-Based Missile Defense System --

DULLES, Va.Dec. 5, 2008--Orbital Sciences Corporation (NYSE:ORB) announced today that its Orbital Boost Vehicle (OBV), which is the booster rocket for the Ground-Based Interceptor (GBI), was successfully launched as part of a test of the Ground-Based Midcourse Defense (GMD) program. Orbital provides the OBV as part of an industry team led by The Boeing Company (NYSE:BA) for the U.S. Missile Defense Agency (MDA). The OBV was launched from Vandenberg Air Force Base, CA earlier today as part of the test designated as Flight Test Ground-based Midcourse Defense-05 (FTG-05). Following its launch from a silo, the OBV flew downrange over the Pacific Ocean and successfully supported the intercept of a target vehicle that was launched earlier from Alaska.

Following a preliminary post-flight analysis of the data collected from the mission, MDA and the GMD team confirmed that all primary OBV objectives for FTG-05 were achieved. These included pre-launch built-in test functionality, launch and flyout of the OBV, accurate delivery of the Exoatmospheric Kill Vehicle (EKV) payload and acquisition of telemetry data for further characterization of the OBV's flight characteristics. The OBV and the EKV make up the GBI, which is assembled by Boeing.

"The FTG-05 test marks the seventh successful flight of our OBV booster, supporting MDA's increasingly realistic flight test conditions of the GMD system," said Mr. Ron Grabe, Orbital's Executive Vice President and General Manager of its Launch Systems Group. "Orbital is extremely proud to be a part of this program that now provides a defensive capability for our homeland and will, in the future, extend that coverage to our European allies as well."

Orbital's GMD boost vehicle is a three-stage rocket based on flight-proven hardware that has flown over 50 times on missions carried out by the company's Pegasus(R), Taurus(R) and Minotaur space launch vehicles. Orbital is developing, manufacturing and testing interceptor vehicles under a multi-year contract from Boeing.

Orbital's space launch vehicles, missile defense interceptors and related suborbital rockets are primarily produced at the company's engineering and manufacturing facility in Chandler, AZ and its vehicle assembly and integration facilities at Vandenberg Air Force Base in California. The company's launch vehicles are used by commercial and government customers to deliver small satellites into low altitude orbits above the Earth and in missile defense systems, both as threat-simulating target vehicles and as interceptor boosters for U.S. national defense systems.

In addition to its launch vehicle systems, Orbital's other primary products are satellites and related space systems, which are also used by commercial, civil government and military customers. These products include low-orbit, geostationary-orbit and planetary spacecraft for communications, remote sensing, scientific and defense missions. Orbital also provides human-rated space systems for Earth-orbit, lunar and other missions, as well as satellite subsystems and space-related technical services to government agencies and laboratories.

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

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

    Source: Orbital Sciences Corporation