• Firm Contract Value from The Boeing Company Now Totals $450 Million -

DULLES, Va., Jan. 10 /PRNewswire-FirstCall/ -- Orbital Sciences Corporation (NYSE: ORB) announced today that it has received approximately $50 million in incremental modifications to its contract from The Boeing Company (NYSE: BA) to develop, test and produce interceptor boost vehicles for the U.S. Department of Defense/Missile Defense Agency's (MDA) Ground-based Midcourse Defense (GMD) System. The company stated that its firm contract value has risen to over $450 million since the original contract was awarded in early 2002. The term of the firm contract extends through 2007. In addition to the firm portion of the contract, Orbital has optional orders for production of approximately 50 interceptor boosters estimated at about $535 million. As currently planned, the term of the optional portion of the contract would begin in 2004 and run through the end of 2009. With the additional firm contract value, the total potential value of Orbital's contract now stands at approximately $1 billion.

The additional $50 million scope of work supports a series of nine demonstration and test flights of Orbital's GMD boost vehicle beginning in early 2003. The test flights include participation in seven GMD Integrated Flight Test (IFT) exercises into 2006. The IFT development test program demonstrates the ability of GMD System elements to work together as an integrated system. As designed, MDA's RDT&E; testbed complex in Fort Greely, Alaska will expand to enhance overall test infrastructure and system maturation.

"We are pleased with how the GMD boost vehicle program is progressing, which is on a very 'fast track' schedule leading to the first demonstration launch in early 2003," said Mr. Ronald J. Grabe, Orbital's Executive Vice President and General Manager of its Launch Systems Group. "Many key electrical components have completed qualification and acceptance testing, assembly of major subsystems is underway and solid rocket motors have been delivered to our missile assembly facility at Vandenberg Air Force Base, California."

Orbital is one of the world's leading developers and manufacturers of affordable space systems for commercial, civil government and military customers. The company's primary products include low-orbit, geosynchronous and planetary spacecraft for communications, scientific and remote sensing missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense boosters that are used as target and interceptor vehicles. Orbital also offers space-related technical services to government agencies and develops and builds satellite-based transportation management systems for public transit and public works agencies, as well as private vehicle fleet operators.

More information about Orbital can be found at http://www.orbital.com

For More Information Contact:

Barron Beneski 703-406-5528

Public and Investor Relations

Beneski.barron@orbital.com SOURCE Orbital Sciences Corporation

-0- 01/10/2003

/CONTACT: Barron Beneski, Public and Investor Relations, of Orbital Sciences Corporation, +1-703-406-5528, or Beneski.barron@orbital.com/