— ISS Cargo System Includes New Cygnus(TM) Maneuvering Spacecraft, Interchangeable Cargo Modules and Taurus II Medium-Lift Launch Vehicle —

— Initial COTS Demonstration Mission Scheduled for Fourth Quarter of 2010 —

(Dulles, VA 19 February 2008) – Orbital Sciences Corporation (NYSE: ORB) announced today that it has been selected by the National Aeronautics and Space Administration (NASA) to demonstrate a new space transportation system for delivering cargo to the International Space Station (ISS). In a three-year, $320 million cooperative program, NASA will invest $170 million and Orbital will contribute $150 million (including its planned Taurus II launch vehicle development investment) in the Commercial Orbital Transportation Services (COTS) project. In its first phase, the COTS project will involve the development and flight demonstration of a commercial cargo delivery system to low Earth orbit with the potential to support ISS operations following the retirement of the Space Shuttle in 2010. This system will consist of a new advanced maneuvering spacecraft called Cygnus(TM), along with several interchangeable modules for pressurized and unpressurized cargo, and will be launched on Orbital’s new Taurus II medium-lift rocket.

The COTS project is strategically important to both NASA and Orbital,” said Mr. David W. Thompson, Orbital’s Chairman and Chief Executive Officer. “For NASA, the ability to deliver cargo to the International Space Station with reasonably priced commercial services is part of its long-term plan to rely on American industry for routine Earth-orbit operations, as the space agency focuses on returning astronauts to the Moon and beyond. For Orbital, the COTS project is a critical element of the company’s strategy to play an expanded role in human spaceflight programs, including ISS operations and the development and support of NASA’s Orion program.”

Orbital’s COTS demonstration mission is scheduled to take place in the fourth quarter of 2010. Subject to NASA’s future requirements, Orbital will be prepared to carry out several follow-on operational COTS missions in 2011 and to conduct as many as eight operational ISS cargo flights a year by 2012 and 2013. The Cygnus spacecraft to be launched aboard the Taurus II rocket will be capable of delivering up to 2,300 kg of cargo to the ISS and will be able to return 1,200 kg of cargo from the ISS to Earth.

The COTS project will provide NASA with a U.S.-produced and -operated automated cargo delivery service for ISS support, to complement Russian, European and Japanese cargo vehicles. In addition, the COTS project will help facilitate the introduction of Taurus II, a new medium-class launch vehicle that can be used by NASA and other government agencies and private-sector satellite operators for a variety of scientific, national defense and commercial space missions.

By serving as an anchor mission for Orbital’s Taurus II rocket, the COTS project will not only benefit NASA’s ISS operations with reliable commercial cargo service once the system is fully operational, but will also aid NASA’s Earth and space science and planetary exploration programs with lower-cost launches of medium-class satellites,” said Dr. Antonio L. Elias, Executive Vice President and General Manager of Orbital’s Advanced Programs Group, which leads a company-wide team developing the Taurus II launch vehicle and the Cygnus spacecraft.

Orbital currently plans to carry out the development, production and integration of the Cygnus spacecraft and cargo modules at company facilities in Dulles, Virginia and Greenbelt, Maryland. The company’s design, manufacturing and testing activities related to the Taurus II rocket will be done in Dulles and Chandler, Arizona. Early COTS missions are planned to be launched from NASA’s Wallops Flight Facility on Virginia’s Eastern Shore, with integrated mission operations conducted from control centers in Dulles and Houston, Texas.

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.

Note to Editors:

High-resolution images of the Cygnus spacecraft and Taurus II space launch vehicle are available to be downloaded from Orbital’s web site at: http://www.orbital.com/NewsInfo/ImagesMultimedia/Images/ExplorationSystems/index.shtml