DULLES, Va., Aug 11, 2003 (BUSINESS WIRE) -- SCISAT-1 Mission Will be the Fourth Pegasus Launch in 2003 and 35th in the Program's History

Orbital Sciences Corporation (NYSE:ORB) today announced that it is in final preparations to launch the Scientific Satellite (SCISAT-1) Atmospheric Chemistry Experiment (ACE) spacecraft for the National Aeronautics and Space Administration (NASA) and the Canadian Space Agency (CSA) aboard the company's Pegasus(R) rocket. The launch is currently scheduled to take place on Tuesday, August 12, 2003 from Vandenberg Air Force Base (VAFB), California during an available launch window that extends from 10:05 p.m. to 11:02 p.m. (EDT). The targeted launch time is approximately 10:10 p.m. This operational schedule is subject to the completion of final pre-launch activities, as well as acceptable weather conditions at VAFB at the time of the launch.

The powered flight sequence for the SCISAT-1 mission is expected to take approximately 11 minutes, from the time the Pegasus rocket is released from the L-1011 carrier aircraft to the time that the satellite is deployed into orbit. Orbital plans to launch the 330-pound SCISAT-1 spacecraft into a polar orbit approximately 400 miles above the Earth, inclined at 73.9 degrees to the equator.

About Pegasus

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.

The SCISAT-1 mission will be the 35th flight of the Pegasus rocket and its fourth mission in 2003. Earlier this year, Pegasus carried out three successful launches, each carrying an Orbital-built satellite, including SORCE in January, GALEX in April, and OrbView-3 in June, which was the 20th consecutive successful mission for the Pegasus rocket.

About SCISAT-1

The SCISAT-1 spacecraft was developed under a cooperative program between NASA and CSA. The Canadian government selected ACE for the scientific mission for the SCISAT-1 spacecraft. The major scientific goal of the ACE instrument is to measure and understand the chemical processes that control the distribution of ozone in the Earth's atmosphere, especially at high altitudes.

The data gathered by SCISAT-1 will help Canadian scientists and policy makers assess existing environmental policy and develop protective measures for improving the health of the Earth's atmosphere and preventing further ozone depletion. The SCISAT-1 mission is designed to last at least two years.

About Orbital

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are satellites 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

    Note to Editors:

    --  High-resolution photos the Pegasus rocket are available on
        Orbital's web site at:

    --  Live television coverage of the Pegasus/SCISAT-1 mission will
        be broadcast on NASA TV beginning at 8:30 p.m. (EDT).
        Television is broadcast on AMC-9, transponder 9C, C-band,
        located at 85 degrees West longitude. The frequency is 3880.0
        MHz. polarization is vertical, and audio is monaural at 6.80
        MHz. Live audio commentary of the launch will also be
        available on NASA's "V" circuit and can be accessed by calling
        (321) 867-1220/1240/1260/7135. NASA will also webcast the
        launch at http://www.ksc.nasa.gov

SOURCE: Orbital Sciences Corporation

Orbital Sciences Corporation
Barron Beneski, 703-406-5528
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