DULLES, Va.April 26, 2005--Orbital Sciences Corporation (NYSE:ORB):

    --  Mach 2.5 Target Vehicle Demonstrates Highly Accurate
        Performance and Over 11-G Maneuvers During Fifth Consecutive
        Successful Flight

    --  Navy Orders 10 More Production Vehicles in $12.5 Million
        Option Exercise

    --  Flight Marks Sixth Rocket and Satellite Mission Conducted by
        Company in Last 30 Days

Orbital Sciences Corporation (NYSE: ORB) announced today that it successfully flight-tested the final development vehicle in the U.S. Navy's GQM-163A "Coyote" Supersonic Sea-Skimming Target (SSST) system for the Naval Air Systems Command (NAVAIR) on April 22, 2005. The flight test was conducted at the Navy's missile test range at Point Mugu in southern California and marked the completion of the SSST's development and flight test program consisting of seven launches over the last two years, including five guided and two unguided launches.

During this most recent mission, the GQM-163A vehicle achieved cruise velocity of Mach 2.5 while traveling approximately 15 meters above the sea surface, and reached a peak velocity of Mach 2.8. While in flight, the highly maneuverable vehicle conducted combined horizontal and vertical maneuvers that exceeded 11-G's of acceleration. It also successfully navigated to, and passed within 20 meters of, a moving remotely controlled target ship at a range of over 50 kilometers from its launch point. The duration of the mission was approximately 120 seconds and covered about 100 kilometers from its initial launch point off the California coast.

Captain Richard Walters, the U.S. Navy's GQM-163A Program Manager, said, "This is the last of five developmental flight tests. Deliveries of production assets later this summer allow us to fill a critical shortfall in the Navy's SSST target inventory. The capabilities of the Coyote will permit us to provide a wide variety of anti-ship cruise missile scenarios, including flight down to 15 feet, speeds approaching Mach 3.0, and sustained accelerations in excess of 10-Gs."

Mr. Keven Leith, Orbital's Vice President of Naval Programs, said, "We are pleased with the results of the GQM-163A flight test program. This final test flight success completes the planned engineering and development test phase, clearing the way for initial Coyote SSST production and operational deployment in support of the fleet's operational test and evaluation."

About the GQM-163 "Coyote" Program

Orbital was awarded an initial development contract in 2000 to meet the Navy's requirement for an affordable SSST system to simulate high-speed anti-ship cruise missiles for fleet training and weapon systems research, development, test and evaluation. With the successful completion of the final developmental flight, the Coyote target vehicle has met or exceeded all planned performance and maneuver levels. Orbital is now beginning the low-rate initial production (LRIP) phase of the program. In addition to the initial 10 LRIP Coyote vehicles already under contract for delivery to the Navy, Orbital recently received a second 10-unit production option exercise, bringing the total production vehicles under contract to 20.

The GQM-163A Coyote target missile design integrates a four-inlet, solid-fuel ducted-rocket ramjet propulsion system into a compact missile airframe 5.5 meters long and 0.35 meters in diameter. Ramjet supersonic takeover speed is achieved using a decommissioned Navy MK 70 solid rocket motor for the first stage. Rail-launched from Navy test and training ranges, the highly maneuverable GQM-163A Coyote achieves cruise speeds of up to Mach 2.8 following the separation of the MK 70 first-stage booster. The range of the target vehicle is approximately 100 kilometers at altitudes as low as 5 meters above the sea surface.

The GQM-163A Coyote program represents a significant milestone for the American aerospace industry by achieving multiple successful flights of a U.S.-built solid-fuel ducted-rocket ramjet. It is also the first successful development and flight test program of a new domestic ramjet missile configuration in over a decade. Orbital is the only U.S. Department of Defense prime contractor to be both developing and operating ramjet-powered missile systems. In addition to developing the GQM-163A Coyote, Orbital provides the Navy with launch services for the MQM-8 VANDAL SSST. The MQM-8 VANDAL is based on the liquid-fuel ramjet-powered Talos missile and has provided the Navy with a legacy SSST until the more capable GQM-163A Coyote was determined to be operational for fleet use.

Orbital is developing and manufacturing the GQM-163A Coyote at its launch vehicle engineering and production facility in Chandler, Arizona. Orbital's major subcontractors include Aerojet-General Corporation in Gainesville, Virginia and Sacramento, California, for the solid-fuel ducted-rocket motor and CEi, Inc. in Sacramento, California, for the vehicle's avionics system.

About Orbital

Orbital develops and manufactures small space and rocket systems for commercial, military and civil government customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous and planetary spacecraft for communications, remote sensing, scientific and defense 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 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