-- Spacecraft Is Performing As Expected Early In Its Mission --

   -- Horizons-2 to Begin Several Weeks of In-Orbit Testing Prior to
                 Commencement of Commercial Service --

DULLES, Va.Dec. 24, 2007--Orbital Sciences Corporation (NYSE:ORB), the world's leading manufacturer of smaller-sized geosynchronous (GEO) communications satellites, announced today that the Horizons-2 satellite was successfully launched into orbit during a mission that took place on Friday, December 21, 2007. The Horizons-2 spacecraft was delivered into its initial orbit by an Ariane 5 rocket launched from the European space launch complex located near the Equator in French Guiana. Results from early tests of the satellite conducted over the weekend indicate that it is operating as planned for this phase of its mission.

Orbital designed, manufactured and tested the Horizons-2 satellite for HORIZONS-2 SATELLITE, LLC, a joint venture between Intelsat, Ltd. of Bermuda and JSAT Corporation of Japan. The spacecraft will occupy an orbital slot at 74 degrees West Longitude to help meet the growing demand for Ku-band satellite communications services in North America. The satellite features both a continental U.S. (CONUS) beam and an East Coast beam, which will extend the spacecraft's coverage to include the Caribbean and parts of Canada. The Horizons-2 satellite was the third Orbital-built GEO communications satellite to be launched in 2007, following the launch, deployment and commissioning of the Intelsat 11 and Optus D2 satellites in October.

"The early results of the mission indicate that the Horizons-2 satellite is performing just as we would expect it to be as we embark on the more extensive set of in-orbit tests and orbit raising maneuvers over the next several weeks," stated Mr. Christopher Richmond, Senior Vice President and head of Orbital's GEO satellite product division. "We are grateful to Arianespace for another excellent launch campaign, resulting in the accurate deployment of the Horizons-2 satellite."

During the next several days, the Horizons-2 satellite will perform a series of orbit-raising burns using its onboard rocket engines to achieve a circular orbit approximately 22,300 miles (35,800 kilometers) above the Earth. For several weeks afterwards, the mission engineering teams from Intelsat, JSAT and Orbital will conduct a comprehensive series of tests to ensure the spacecraft is ready for final hand-over to the customer.

Orbital's commercial satellite business has experienced rapid growth over the past several years. Including the seven new orders the company has booked so far this year, Orbital currently has nine commercial GEO satellites and five science and defense spacecraft in various stages of design, production and testing at its Dulles, VA satellite manufacturing facility. To accommodate this rapid rate of growth, earlier this year Orbital completed an expansion of its manufacturing plant that, together with other facility improvements, has increased its manufacturing throughput capacity by over 30% as compared to one year ago.

About Orbital

Orbital develops and manufactures small rockets and space 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.

Note to Editor: High-resolution images of the Horizons-2 are available on Orbital's web site at: http://www.orbital.com/NewsInfo/Images/GEO/index.html

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

    SOURCE: Orbital Sciences Corporation