-- Orbital TMS Secures First Contract to Enhance System Efficiency,
         Safety and Security for Drivers and Students Aboard a
                    Large-Scale School Bus Fleet --

       -- Company to Outfit Fleet of 685 Buses with State-of-the-Art
    Vehicle Management System that Includes Two-Way Communications
      Capabilities, Vehicle Location Information and Video-Based
                    Safety and Security Package --

DULLES, Va.July 23, 2007--Orbital Sciences Corporation (NYSE:ORB) announced today that its Transportation Managements Systems division (Orbital TMS) has been awarded its first contract to install a vehicle management system to track a large-scale fleet of school buses. The Metropolitan Nashville Public Schools (MNPS) in Nashville, Tennessee has selected Orbital TMS for a $9 million contract to install its latest integrated fleet management system to help the Metropolitan Nashville School District improve the effectiveness and safety of its school bus service. This product suite will give MNPS the real-time and analytical tools to enable them to improve the overall efficiency of its 685-vehicle fleet operations.

Mr. A. David Kachemov, Senior Vice President and General Manager of Orbital TMS, said, "Orbital is eager to begin work with MNPS to install our products that will increase the overall level of safety and system coordination that MNPS is able to offer the students of Nashville. Our flexible solution, innovative products and dedicated team of professionals will assist MNPS and the community at large by improving situational awareness as well as providing new features that enhance the school system's transportation services."

Orbital has worked with MNPS to develop a timeline that will deliver the entire system in a three-phase approach over an estimated 36-month period. Based on MNPS' requirements, the project will begin with the installation of an 800 MHz two-way voice communications radio system in all of the vehicles. Once the communications system is operational, Orbital TMS' OrbCAD system, an integrated software system that uses satellite-delivered positioning information to track vehicles along prescheduled routes, will be installed at MNPS' control center and on the entire fleet of school buses and administrative vehicles.

The OrbCAD product provides comprehensive fleet management capabilities and a supporting information terminal, known as OrbStar, which provides detailed turn-by-turn navigational directions on a color-display terminal to school bus drivers for the hundreds of different routes that are operated. This system configuration will benefit MNPS by giving school bus drivers more accurate information on their assigned route and by allowing for improved responsiveness should detours, emergencies or other unplanned events occur. The last phase of the project will include equipping the fleet with video cameras for enhanced safety and security of MNPS' 74,000 students and its school bus operators.

Mr. Kachemov added to his earlier remarks, stating, "This agreement proves that Orbital's products are beneficial to a variety of transportation services, from public transit systems to highway maintenance vehicles and from private vehicle fleets and light rail systems to large-scale school bus systems, our products make their operations more efficient, improve customer service and add new levels of safety and security for both the operators and the public-at-large. These various types of vehicle fleets can realize the benefits of the OrbCAD system and its vehicle components. In addition, the OrbCAD XP system's open architecture will allow MNPS and our other customers to add new features in the future as transportation systems continue to grow."

About Orbital TMS

Orbital TMS is a leading integrator of products for fleet and workforce management, mobile data communications, data management, and advanced traveler information systems. TMS provides integrated Computer Aided Dispatch (CAD) and Automatic Vehicle Location (AVL) solutions for 60 public transit and state agency customers in the U.S. and internationally, with units installed or scheduled to be installed on approximately 28,000 vehicles. More information about Orbital TMS can be found at http://www.orbitaltms.com

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-orbit 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. More information about Orbital 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