DULLES, Va.Sept. 1, 2006--Orbital Sciences Corporation (NYSE:ORB) announced today that its Orbital Boost Vehicle (OBV) 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 interceptor missile was launched from Vandenberg Air Force Base, CA earlier today at 1:39 p.m. (Eastern) as part of the test designated as Flight Test-2 (FT-2). 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 at 1:22 p.m. (Eastern).

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 FT-2 were achieved or exceeded. 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.

"We continue to be very pleased with the operation and performance of the OBV interceptor, as clearly demonstrated by the excellent results from the Flight Test-2 mission," said Mr. Ron Grabe, Orbital's Executive Vice President and General Manager of its Launch Systems Group. "Orbital is proud of the critical role we play in helping deter and prevent a ballistic missile attack against our country and our allies."

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 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 offers space-related technical services to government agencies and develops and builds satellite-based transportation management systems for public transit agencies and private vehicle fleet operators.

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

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

    SOURCE: Orbital Sciences Corporation