DULLES, Va.July 14, 2004--

Company-Built Autonomous Rendezvous Technology Demonstration Vehicle

to be Launched for NASA Aboard 36th Pegasus Rocket Later this Year

Orbital Sciences Corporation (NYSE:ORB) today announced that its Demonstration of Autonomous Rendezvous (DART) spacecraft has arrived at the company's integration and processing facilities at Vandenberg Air Force Base (VAFB), California for final testing and prelaunch preparations before its launch into orbit. The DART vehicle, which is about six feet long and three feet in diameter and weighs about 800 pounds, will be launched aboard the 36th flight of Orbital's Pegasus(R) space launch vehicle later this year into a polar orbit approximately 475 miles above the Earth. Orbital designed and built the DART spacecraft in Dulles, Virginia for NASA's Marshall Space Flight Center located in Huntsville, Alabama.

The DART vehicle is a technology demonstration platform designed to test the technologies required for a spacecraft to locate and rendezvous with another spacecraft without direct human guidance. While NASA has performed rendezvous and docking missions in the past, such as the Space Shuttle locating and docking with the International Space Station (ISS), astronauts have always piloted the spacecraft. The DART mission will be performed autonomously by onboard computer systems without direct human involvement in the control of the vehicle. The technologies demonstrated by DART represent a critical step forward in establishing an autonomous rendezvous capability for the United States, laying the groundwork for future reusable manned and unmanned launch vehicle operations. Future applications of this technology include cargo delivery, in-orbit space assembly and other on-orbit activities such as satellite retrieval and servicing missions.

Following its launch aboard the Pegasus rocket, DART will perform a series of in-orbit maneuvers to arrive at a point near a target satellite using state-of-the-art Global Positioning System (GPS) navigation techniques. Using the vehicle's main instrument, the Advanced Video Guidance Sensor (AVGS), DART will then approach the target satellite and perform a series of proximity operations including station keeping, docking axis approaches and circumnavigation. Finally, the vehicle will demonstrate a collision avoidance maneuver and then depart the vicinity and transition to its final orbit. The entire mission sequence will be accomplished under autonomous control and will be completed in under 24 hours.

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:

    --  For more information about the DART mission, visit Orbital's
        web site at: http://www.orbital.com/AdvancedSpace/DART/

    --  NASA's Marshall Space Flight Center also maintains DART
        mission information on its web site at:

    --  High-resolution images, suitable for publication, are
        available on both Orbital's and NASA's Marshall Space Flight
        Center web sites at:

    CONTACT: Orbital Sciences Corporation
             Public and Investor Relations:
             Barron Beneski, 703-406-5528

    SOURCE: Orbital Sciences Corporation