DULLES, Va.April 28, 2006--Orbital Sciences Corporation (NYSE:ORB):

    --  New 12-Month Buy-Back Program Replaces Company's Previous
        Repurchase Program that Expired Earlier this Month

    --  Company Repurchased Approximately 4.0 Million Shares for $46
        Million Under Previous 12-Month Program

Orbital Sciences Corporation (NYSE:ORB) today announced that its Board of Directors has authorized the company to repurchase up to $50 million of its outstanding securities over the next 12 months. The repurchases could include shares of Orbital's common stock, its senior notes, its stock warrants or any combination of the three securities.

"The securities repurchase authorization by our Board reflects the company's commitment to return value to our shareholders," said Mr. David W. Thompson, Chairman and Chief Executive Officer. "Orbital's healthy cash balances and continued strong free cash flow outlook provide us with the flexibility to further improve the company's capital structure in meaningful ways."

The Board's authorization replaces a previous 12-month, $50 million securities repurchase program that expired earlier this month. Under that program, Orbital repurchased a total of 3.95 million common shares, or about six percent of its basic outstanding shares, for $46.1 million, at an average of approximately $11.66 per share.

Under the newly authorized repurchase program, shares of common stock may be purchased from time to time in the open market, in block purchase or in negotiated transactions. The notes and warrants may be purchased in negotiated transactions. The timing, amount and type of securities to be repurchased will be determined based on market conditions and other factors.

The following outstanding securities are subject to the repurchase program: 55.2 million shares of common stock; $126 million of 9% senior notes due 2011; and warrants to purchase approximately 7.3 million shares of common stock with an exercise price of $3.86 that expire on August 31, 2006.

About Orbital

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are satellites and launch vehicles, including low-orbit, geostationary-orbit and planetary spacecraft for communications, remote sensing and scientific missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense boosters 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.

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

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

    SOURCE: Orbital Sciences Corporation