DULLES, Va.May 20, 2004--

       Mission Marks Debut of Enhanced Performance Configuration
           of Company's Ground-Launched Space Launch Vehicle

Orbital Sciences Corporation (NYSE:ORB) announced today that its Taurus XL space launch vehicle successfully boosted the Republic of China's ROCSAT-2 remote sensing satellite into low-Earth orbit in a mission that originated from Vandenberg Air Force Base in California earlier this afternoon. Today's mission was the seventh in the Taurus program's history and was also the inaugural flight of the enhanced performance "XL" version of the space launch vehicle.

At approximately 1:47 p.m. (EDT), following the ignition of the Taurus first stage motor, the rocket lifted-off from launch pad 576E at Vandenberg and flew its trajectory over the Pacific Ocean. Approximately 14 minutes later, the ROCSAT-2 satellite separated from the final stage of the Taurus booster and was placed into orbit approximately 735 kilometers above the Earth, inclined at 99.1 degrees to the equator. Preliminary results indicate that the ROCSAT-2 satellite is operating as planned in the early stages of its mission.

Mr. Ron Grabe, Orbital's Executive Vice President and General Manager of its Launch Systems Group, said, "We are very pleased with the results of the Taurus launch and wish our customers from Taiwan's National Space Programs Office the very best with their satellite mission. Today's successful launch sets the stage for Orbital's continued support for the ROCSAT program. As the prime contractor for the upcoming ROCSAT-3 constellation of six small satellites, as well as the launch vehicle provider for that mission, we look forward to contributing to the continued success of the National Space Program Office's space missions."

About Orbital Sciences Corporation

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.

Note to editors: High-resolution photos of the launch of the Taurus rocket will be available on Orbital's web site at: http://www.orbital.com/NewsInfo/MissionUpdates/t7.html

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

    SOURCE: Orbital Sciences Corporation