-- Activities Under 10-Year $100 Million TSER Contract to be

              Managed by White Sands Missile Range, NM --

DULLES, Va.May 6, 2008--Orbital Sciences Corporation (NYSE:ORB) announced today that it has been awarded a contract by the U.S. Department of Defense for the Theoretical Studies and Engineering Services (TSER) program. Orbital will serve as a prime contractor to support U.S. Army, Navy and Air Force research and development programs managed by White Sands Missile Range (WSMR) in New Mexico. The basic term of the indefinite delivery/indefinite quantity (IDIQ) TSER contract is for five years, with an option for an additional five years. The total value of the contract is up to $100 million for the full ten-year period.

"Orbital is very excited to be supporting the White Sands Missile Range as a new customer," said Mr. Ron Wiley, Orbital's Senior Vice President of Suborbital Launch Vehicle Programs. "The TSER contract award is another example of Orbital's leadership position in the design, development and operation of suborbital rockets used to support Department of Defense research and target rocket programs."

In addition to the White Sands-based prime contract under the TSER program, Orbital is also a member of a separate Northrop Grumman TSER team, with company activities centered at Wallops Flight Facility in Virginia.

Orbital is one of the country's most experienced manufacturers and operators of short-, medium- and long-range suborbital boosters, science-related sounding rockets and high-speed anti-ship cruise missile targets. These launch systems are primarily used to test defensive weapons systems or to carry out exoatmospheric scientific and weather-related research projects. Among the several hundred missions of these types that Orbital has carried out over the last 25 years, approximately 140 of them have been conducted from WSMR.

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 Earth-orbit, geosynchronous Earth-orbit and planetary spacecraft for communications, remote sensing, scientific and defense missions; human-rated space systems for Earth-orbit, lunar and other 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 software-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
             Barron Beneski, 703-406-5528
             Public and Investor Relations

    SOURCE: Orbital Sciences Corporation