Orbital Sciences to Announce Quarterly Numbers

PRESS RELEASE

Orbital Sciences Corporation (NYSE: ORB) announced today that it will release its first quarter 2009 financial results prior to the opening of the market on Tuesday, April 28, 2009.

Orbital will also conduct a conference call with financial analysts and investors the same morning, beginning at 9:00 a.m. (EST). 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 95460998. A replay of the conference call will be available approximately two hours after the end of the call and will remain active until Tuesday, May 5, 2009. For access to the replay of the conference call, dial (800) 642-1687 (international callers should dial (706) 634-7258) and use the same conference ID number.

For webcast registration and information, please visit Orbital’s web site at http://www.orbital.com/Investor. The company advises participants to register at least 20 minutes prior to the call to download and install any necessary audio software.