Orbital's First Operational Missile Defense Interceptor Vehicle Emplaced in Silo at Fort Greely, Alaska.

DULLES, Va. -- Company On Track to Meet U.S. Missile Defense Agency's Deployment Requirement for Up To 20 Interceptor Boosters by the End of 2005, Plus Additional Vehicles for Robust Test Program

Orbital Sciences Corporation (NYSE:ORB) announced that it supplied the first interceptor boost vehicle for the U.S. Missile Defense Agency (MDA)'s Ground-based Midcourse Defense (GMD) system that was installed into an underground silo at Fort Greely, Alaska yesterday, July 22, 2004. The company also stated that it has delivered several other Orbital Boost Vehicle (OBV) interceptors that are scheduled for emplacement over the next several weeks and is currently producing additional vehicles at its facilities at Vandenberg Air Force Base (VAFB), California. The company is currently on schedule to meet MDA's goal of deploying up to 10 operational interceptors by the end of 2004 and up to 20 operational interceptors by the end of 2005. The current plan calls for 16 OBVs to be deployed at Fort Greely and up to four OBVs to be deployed at VAFB by the end of next year. Orbital will also supply OBV interceptor rockets and several target vehicles to support the robust GMD testing program MDA has planned for the next several years.

"This is a very proud moment for all of Orbital's employees," stated Mr. Ron Grabe, Executive Vice President and General Manager of its Launch Systems Group. "To have Orbital's expertise in interceptor vehicle technology play such a key role in helping defend the United States from the threat of ballistic missile attack is a true honor. We place the utmost importance on our role in the GMD program and regard it as our highest calling."

Over the next several weeks, the three-stage OBV, which will carry an exoatmospheric "kill vehicle" designed to collide with and destroy a hostile long-range missile in the midcourse phase of its flight, will be integrated with the Defense Department's network of early warning sensors, long-range radars, and command and control, battle management and communications systems. When operational, the GMD system will be operated by the U.S. Northern Command and will be an integral part of the planned multi-layer ballistic missile defense system designed to detect, intercept and destroy ballistic missiles to protect the U.S. homeland, deployed U.S. troops and nations.

Orbital's GMD boost vehicle is a three-stage rocket based on flight-proven hardware that has flown about 50 times on previous 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 The Boeing Company (NYSE:BA), MDA's lead system integrator for the GMD program.

About Orbital

Orbital's space launch vehicles, missile defense interceptors and related suborbital rockets are primarily designed and produced at the company's engineering and manufacturing facility in Chandler, Arizona 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 orbits about 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, geosynchronous and planetary spacecraft for communications, remote sensing, scientific missions and national security. In addition, Orbital 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.