-- Rocket Assembly, Ground Operations Procedures and Range Safety

Requirements Planned, Rehearsed and Reviewed by Orbital and U.S. Air

                          Force Officials --

DULLES, Va.Sept. 16, 2008--Orbital Sciences Corporation (NYSE:ORB) today announced that it has completed the full-scale "pathfinder" ground operations of the Minotaur IV space launch vehicle in preparation for its inaugural flight that is currently scheduled to take place in early 2009. The ground testing activities included the assembly of a full-scale Minotaur IV rocket, using inert rocket motors and flight-qualified structures to fully validate all interfaces with the booster, ground support equipment and facility structures. The pathfinder operations were overseen by representatives from the U.S. Air Force organizations that will play critical roles in the Minotaur IV launch operations. These include the U.S. Air Force Space and Missile Systems Center, the U.S. Air Force Space and Development Test Wing, and 30th Space Wing based at Vandenberg Air Force Base (VAFB) in California. The Spaceport Systems International launch pad at VAFB will be the launch site for all three Minotaur IV missions planned in 2009.

"The completion of our pathfinder ground operations test is a major step forward as we proceed toward the inaugural launch of the Minotaur IV launch vehicle," said Mr. Lou Amorosi, Orbital's Vice President with responsibility for its entire Minotaur launch vehicle product line. "In conjunction with our customers and partners that will play vital roles during actual launch operations, we are taking a very methodical and comprehensive approach to ensuring that all aspects of the launch vehicle preparations, ground operations and range safety systems are meticulously planned, rehearsed and reviewed."

The completion of the pathfinder testing activities is a critical milestone in the development of the Minotaur IV launch vehicle. It serves as a rehearsal of all hazardous lifting operations, a fit-check for all vital rocket and ground interfaces, a final test of the mission's ground support equipment, and a checkout of vehicle integration procedures. The extensive pre-launch activities also enhance training of the launch crew and facility personnel.

Prior to beginning the pathfinder operations, procedures for all hazardous operations were approved by range safety officials and the ground support equipment involved in the procedures was proof-tested to range safety standards prior to use. The pathfinder operation was the final test of new Minotaur IV structures, which had recently been fully-qualified to military-standard levels.

During the pathfinder, the various vehicle stages and components were transported, assembled and stacked at the launch site. Once the vehicle was fully assembled, a day-of-launch shelter rollback was rehearsed. Subsequent to those operations, abort operations were also rehearsed and timed before the vehicle was de-stacked and transported back to the integration facility.

The ground operations also included rehearsal of spacecraft encapsulation procedures within the launch vehicle fairing. The Minotaur IV design provides for separate spacecraft encapsulation, which is an enabling procedure for Operationally Responsive Space (ORS) missions, by streamlining the time and sequence of spacecraft encapsulation. Spacecraft can be selected for launch, mated, encapsulated and transported to the launch site independent of other launch vehicle or range operations.

About Orbital

Orbital develops and manufactures small- and medium-class 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 provides satellite subsystems and space-related technical services to government agencies and laboratories.

Note to Editor: A high-resolution image of the Minotaur IV pathfinder vehicle is available on Orbital's web site at: http://www.orbital.com/images/high/Minotaur-IV_Launchpad.jpg

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

    SOURCE: Orbital Sciences Corporation