DULLES, Va.May 18, 2004--Orbital Sciences Corporation (NYSE:ORB) announced today that it is in final preparations to launch its Taurus(R) space launch vehicle carrying the Republic of China's ROCSAT-2 remote sensing satellite on Thursday, May 20, 2004. The mission will originate from Vandenberg Air Force Base (VAFB), California. The available launch window extends from 10:47 a.m. to 11:11 a.m. (Pacific time), with a targeted launch time at the opening of the launch window. This schedule is subject to the completion of final preparations and testing, as well as acceptable weather conditions at VAFB at the time of the mission.

Onboard Orbital's four-stage ground-launched Taurus rocket will be the ROCSAT-2 spacecraft, built for Taiwan's National Space Program Office (NSPO) by EADS/Astrium. ROCSAT-2 is a 750 kg panchromatic and multispectral remote sensing satellite that will observe and monitor the terrestrial and marine environment of Taiwan and surrounding waters. The satellite also carries an instrument to observe lightning in the Earth's upper atmosphere.

On launch day, the Taurus rocket will be prepared for its mission during a four-hour countdown procedure. Following a final launch decision, the vehicle will ignite its first stage rocket motor, lift off and follow a pre-programmed launch sequence controlled by its onboard flight computer. Approximately 14 and a half minutes after liftoff, Taurus will deliver NSPO's ROCSAT-2 spacecraft into a circular parking orbit approximately 725 kilometers above the Earth, inclined at 99.1 degrees to the equator.

About the Taurus Launch Vehicle

Orbital developed the ground-launched Taurus vehicle to provide a cost-effective, reliable means of launching satellites weighing up to approximately 1,375 kg (3,000 pounds) into low-Earth orbit. Taurus incorporates advanced structural and avionics technology proven on Pegasus and other operational launch systems. It is also designed for easy transportability and austere site operations, offering customers rapid-response launches from a wide range of locations. The ROCSAT-2 mission will be the seventh flight of the Taurus rocket, with five of the six previous missions having been fully successful. This mission will also be the first launch of the Taurus XL configuration, which offers greater lift capability compared to previous versions of the Taurus rocket.

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.


    Notes to Editors:

    --  Orbital has developed an online media kit containing further
        information and images about the launch. The media kit can be
        found at:
        http://www.orbital.com/NewsInfo/MissionUpdates/t7.html

    --  On launch day, Orbital will broadcast live video of the launch
        via satellite from Vandenberg Air Force Base, beginning at
        1:30 p.m. (EDT). For satellite coordinate information please
        check the following link:
        http://www.orbital.com/NewsInfo/MissionUpdates/t7.html



    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528
             beneski.barron@orbital.com

    SOURCE: Orbital Sciences Corporation