DULLES, Va.June 16, 2006--Orbital Sciences Corporation (NYSE:ORB) announced today that its Transportation Management Systems (TMS) division has been awarded a contract by Montgomery County Ride On, the public transit system in Montgomery County, Maryland, for the first of a three-phase project to upgrade its current fleet management system, which was originally installed by Orbital TMS in 1996. The first phase of the contract is valued at $3.0 million, with the two follow-on phases having a combined value of another $3.1 million.

Under the new contract, Ride On will upgrade its current Computer Aided Dispatch (CAD) and GPS-based Automatic Vehicle Location (AVL) system as part of a continual improvement process in order to enhance system performance and increase functionality. Orbital's upgraded CAD/AVL system, called OrbCAD XP, will lead to greater levels of customer service and transit system safety for Ride On's passengers. Orbital and Ride On worked to develop a cost-effective three-phase project plan that will allow for seamless operations during the period when the transit bus fleet is being upgraded to the new system.

"Montgomery County and Orbital TMS have a long and mutually rewarding relationship," said Alfie Steele, Acting Chief of Operations for the Division of Transit Services. "We are excited by this opportunity to continue working with Orbital and are very happy with the level of commitment to complete each phase on time," he added.

Ride On has been one of Orbital's long-standing customers for its fleet management products. It has utilized Orbital's UNIX-based OrbCAD fleet management system since 1996. Located in the metropolitan Washington, DC area, Ride On serves the Montgomery County population in such cities as Bethesda, Rockville and Silver Spring with its 390 buses.

"Orbital is extremely pleased that Montgomery County has chosen to implement the OrbCAD XP system so that Ride On can continue to offer best-in-class customer service and overall system responsiveness for its ridership," stated Mr. A. David Kachemov, Senior Vice President and General Manager of Orbital TMS. "Supporting our long-term customers is paramount in our business and this upgrade will offer substantial benefits for the citizens of Montgomery County."

By upgrading to Orbital's next-generation CAD/AVL system, Ride On will receive the latest management tools that have been developed for other customers, such as Singapore's public transit system, which are now being applied to other public transit systems in North America. The highlights of the upgraded OrbCAD XP system include new route and schedule adherence tools, transit service summary updates and high accuracy Automatic Passenger Counters that monitor passenger activity to enable real-time management of passenger capacity and more accurate long-term planning. The system also integrates passenger-friendly features such as onboard automatic voice annunciation that publicly states the vehicle's next stop.

About Orbital TMS

Orbital TMS is the country's leading supplier of satellite-based Automatic Vehicle Location (AVL) systems for the expanding Intelligent Transportation Systems market. Orbital's AVL systems are used by 55 transit and state agency customers in the U.S. and abroad, with units installed or scheduled to be installed on approximately 26,000 vehicles. More information about Orbital TMS can be found at http://www.orbitaltms.com.

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-orbit 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 Sciences Corporation can be found at http://www.orbital.com.

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

    SOURCE: Orbital Sciences Corporation