DULLES, Va.Jan. 27, 2004--

Company's GMD Interceptor Booster Launches Mock Kill Vehicle From Kwajalein Test Site

Orbital Sciences Corporation (NYSE:ORB) announced today that the company's missile defense interceptor boost vehicle, being developed and manufactured for the U.S. Missile Defense Agency's (MDA) Ground-based Midcourse Defense (GMD) system, carried out its third fully successful test flight late yesterday. As part of MDA's Integrated Flight Test-13b (IFT-13b), Orbital's GMD interceptor vehicle, which carried a mock kill vehicle to simulate actual mission operations, was launched from a silo at approximately 9:23 p.m. (EST) on January 26, 2004. The IFT-13b flight originated from the Reagan Test Site on Kwajalein Atoll in the Marshall Islands, located in the mid-Pacific Ocean.

Following preliminary post-flight analysis of the data collected from the mission, Orbital confirmed that all primary objectives for the vehicle's third launch were achieved. The objectives for the mission included the second demonstration of the vehicle's silo-launch capabilities, the verification of the vehicle's design and flight characteristics while carrying a simulated kill vehicle, and further confirmation of the planned performance of its guidance, control and propulsion systems.

Orbital's GMD boost vehicle is a three-stage rocket based on flight-proven hardware that has flown over 45 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 The Boeing Company (NYSE:BA).

"We are very pleased that our GMD interceptor vehicle successfully carried out its role in the integrated flight test," said Mr. Ron Grabe, Executive Vice President and General Manager of Orbital's Launch Systems Group. "We have continued to meet the progressively more challenging test conditions for our vehicle, which will lead to more extensive testing and operational deployment later this year."

The successful launch of the GMD boost vehicle was the company's first space mission in 2004 following two consecutive years of fully successful missions encompassing 26 rocket launches and satellite deployments. Orbital is expecting 2004 to be one of the busiest years in its history, with approximately 20 major space missions and up to 20 additional system deliveries to be completed for a wide range of military, scientific and commercial missions for domestic and international customers.

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, 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 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 and planetary spacecraft for communications, remote sensing and scientific missions. 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.

    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528

    SOURCE: Orbital Sciences Corporation