DULLES, Va.March 16, 2007--Orbital Sciences Corporation (NYSE:ORB) announced that it intends to file with the Securities and Exchange Commission on or about March 26, 2007 a registration statement on Form S-3 (the "Registration Statement") for the resale under Rule 415 of the Securities Act of 1933, as amended, of the Company's previously issued 2.4375% Convertible Senior Subordinated Notes due 2027 (the "Notes") and the common shares, par value $0.01 per share (the "common shares" and, together with the Notes, the "Registrable Securities"), of the Company which may, under certain circumstances, become issuable upon conversion of the Notes. The Notes were originally issued on December 13, 2006; at the same time a Registration Rights Agreement (the "Registration Rights Agreement") was entered into among the Company and the initial purchasers of the Notes, which requires the filing of the Registration Statement. The Company will not receive any of the proceeds from the resale of the securities.

In accordance with the Registration Rights Agreement, beneficial holders of the Registrable Securities that wish to use the Registration Statement in connection with a resale of their Registrable Securities, must complete the Selling Securityholder Notice and Questionnaire, copies of which can be obtained by contacting the General Counsel at the Company at the below address. Once received, please return this completed and executed document for receipt by the Company on or before March 23, 2007.

General Counsel
Orbital Sciences Corporation
21839 Atlantic Boulevard
Dulles, Virginia 20166
Phone: (703) 406-5524
Fax: (703) 406-5572

This communication shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any state or other jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or other jurisdiction.

About Orbital

Orbital develops and manufactures small space and missile systems for commercial, civil government and military customers. Orbital's primary products are satellites and launch vehicles, including low-orbit, geosynchronous-orbit and planetary spacecraft for communications, remote sensing, scientific and defense 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

Safe Harbor Statement

Certain statements in this press release may be forward-looking in nature or "forward-looking statements" as defined in the Private Securities Litigation Reform Act of 1995. Such forward-looking statements are subject to risks, trends and uncertainties that could cause the actual results or performance of the company to be materially different from the forward-looking statement. Uncertainty surrounding factors such as continued government support and funding for key space and defense programs, product performance and market acceptance of products and technologies, the outcome of the government investigation, as well as other risk factors and business considerations described in the company's SEC filings, including its annual report on Form 10-K, could impact Orbital's actual financial and operational results. Orbital assumes no obligation for updating the information contained in this press release.

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

    SOURCE: Orbital Sciences Corporation