9:00 a.m. Conference Call with Financial
                     Analysts and Investors to be Webcast

DULLES, Va., April 21 /PRNewswire-FirstCall/ -- Orbital Sciences Corporation (NYSE: ORB) announced today that it will release its first quarter 2003 financial results prior to the opening of the market on Thursday, April 24, 2003. Orbital will also conduct a conference call with financial analysts and investors the same morning, beginning at 9:00 a.m. (EDT). The conference call will be hosted by:

    * Mr. David W. Thompson, Chairman and Chief Executive Officer
    * Mr. Garrett E. Pierce, Vice Chairman and Chief Financial Officer
    * Mr. James R. Thompson, Vice Chairman and Chief Operating Officer

To listen to the conference call, dial (888) 541-8767, and use the conference ID number 9920430. A replay of the conference call will be available approximately two hours after the end of the call and will remain active for one week, until Thursday, May 1, 2003. For access to the replay of the conference call, dial (800) 642-1687 (international callers should dial (706) 645-9291) and use the same conference ID number.

The conference call will also be webcast. For webcast registration and information, please visit Orbital's web site at http://www.orbital.com/Investor. It is advisable to register at least 20 minutes prior to the call to download and install any necessary audio software. A transcript of the conference call will be posted on the investor relations section of Orbital's web site within 48 hours.

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are spacecraft and launch vehicles, including low-orbit, geostationary 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: Barron Beneski, Public and Investor Relations, of Orbital Sciences Corporation, +1-703-406-5528, beneski.barron@orbital.com.

SOURCE  Orbital Sciences Corporation
    -0-                             04/21/2003
    /CONTACT:  Barron Beneski, Public and Investor Relations, of Orbital
Sciences Corporation, +1-703-406-5528, beneski.barron@orbital.com/
    /Web site:  http://www.orbital.com http://www.orbital.com/Investor/

CO:  Orbital Sciences Corporation
ST:  Virginia

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8640 04/21/2003 13:49 EDT http://www.prnewswire.com