Mission Was 33rd Flight of Air-Launched Pegasus
                   Rocket and its 19th Consecutive Success

   Orbital-Built GALEX Satellite Operating as Planned Early in the Mission

DULLES, Va., April 28 /PRNewswire-FirstCall/ -- Orbital Sciences Corporation (NYSE: ORB) announced that earlier today, it successfully launched the National Aeronautics and Space Administration (NASA)'s Galaxy Evolution Explorer (GALEX) satellite into its targeted orbit aboard the company's Pegasus(R) rocket. The 312-kilogram (690-pound) GALEX scientific satellite, which Orbital designed and built at its Dulles, Virginia satellite manufacturing facility, was accurately delivered into its targeted orbit approximately 690 kilometers (420 miles) above the Earth, inclined at 29 degrees to the equator.

The powered flight sequence for the GALEX mission took about 11 minutes, from the time the Pegasus rocket was released from its L-1011 carrier aircraft at approximately 8:00 a.m. (EDT) to the time that the satellite was deployed into orbit. Preliminary information indicates that the GALEX satellite is working as planned in the early stages of its mission.

Pegasus is the world's leading launch system for the deployment of small satellites into low-Earth orbit. Its patented air-launch system, in which the rocket is launched from beneath Orbital's "Stargazer" L-1011 carrier aircraft over the ocean, reduces cost and provides customers with unparalleled flexibility to operate from virtually anywhere on Earth with minimal ground support requirements.

Pegasus is the only small launch vehicle to have earned NASA's Category 3 certification, which allows the U.S. space agency to launch its most valuable payloads aboard the rocket. A Category 3 certification is achieved through a long-term record of highly reliable launch services, such as the current record of 19 consecutive successful Pegasus missions carried out since 1997.

The GALEX mission was the 33rd flight of the Pegasus rocket and the second of four planned missions in 2003. In January, Orbital successfully launched another company-built satellite, SORCE, for NASA aboard Pegasus. Orbital's next launch will be the OrbView-3 high-resolution imaging satellite, which the company built for ORBIMAGE, in early June. Orbital is also scheduled to launch the SCISAT scientific spacecraft for NASA/Kennedy Space Center and the Canadian Space Agency later in 2003.

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are spacecraft and launch vehicles, including low-orbit, geostationary and planetary spacecraft 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 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: Barron Beneski, Public and Investor Relations of Orbital Sciences Corporation, +1-703-406-5528, or Beneski.barron@orbital.com.

SOURCE  Orbital Sciences Corporation
    -0-                             04/28/2003
    /CONTACT:  Barron Beneski, Public and Investor Relations of Orbital
Sciences Corporation, +1-703-406-5528, or Beneski.barron@orbital.com/
    /Web site:  http://www.orbital.com/

CO:  Orbital Sciences Corporation; National Aeronautics and Space
     Administration; NASA
ST:  Virginia

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8593 04/28/2003 10:40 EDT http://www.prnewswire.com