DULLES, Va.Aug. 8, 2005--Orbital Sciences Corporation (NYSE:ORB) announced today that it successfully launched a medium-range target vehicle that supported the U.S. Missile Defense Agency's (MDA) Critical Measurements and Countermeasures Program, Campaign 1 (CMCM-1). The launch of Orbital's medium-range Castor IVB(R) target vehicle originated from Kauai Test Facility at the Pacific Missile Range Facility on August 4, 2005. Orbital's role in the test, which was led by the company's Launch Systems Group in Chandler, AZ, was to supply the boost vehicle, to integrate the Massachusetts Institute of Technology Lincoln Laboratories payload deployment module and Sandia National Laboratories reentry system, and to conduct launch operations as contracted by the U.S. Army Space and Missile Defense Command.

"We are very proud to have successfully carried out another critical target vehicle mission for the U.S. missile defense effort," said Mr. Ronald D. Wiley, Orbital's Senior Vice President of Suborbital Launch Vehicles. "This flight test was of particular significance, as an important phenomenology and data collection mission for missile defense systems, and also demonstrated another variant of Orbital's flexible medium-range target vehicles in a ground-launched configuration."

Orbital is one of the country's most experienced suppliers and operators of suborbital boosters and anti-ship cruise missile targets that are used to test defensive weapons systems. In addition to the Critical Measurements and Countermeasures Program, Orbital supplies target vehicles for MDA's Ground-based Midcourse Defense System (GMDS), U.S. Navy's Aegis Ballistic Missile Defense System, and the U.S. Army's Patriot (PAC-3) and Theater High Altitude Area Defense (THAAD) Systems.

Orbital is one of the world's leading developers and manufacturers of affordable space systems for commercial, civil government and military customers. The company's primary products are spacecraft and launch vehicles, including geostationary and low-orbit satellites for communications, remote sensing and scientific missions; ground and air-launched rockets that deliver satellites into orbit; and missile defense boosters that are used as interceptors 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