DULLES, Va.Dec. 20, 2006--Orbital Sciences Corporation (NYSE:ORB) announced today that, in connection with the previously announced cash tender offer and consent solicitation for its outstanding 9% Senior Notes due 2011, Orbital has received the requisite consents from holders of the 9% Senior Notes to amend the indenture governing the 9% Senior Notes (the "Indenture"). Orbital also announced today that it has determined the consideration to be paid for the 9% Senior Notes in the tender offer.

As of 5:00 p.m., New York City time, on December 20, 2006 (the "Consent Payment Deadline"), tenders and consents had been received with respect to $ 125,910,000 aggregate principal amount of the 9% Senior Notes (approximately 99.59% of the total outstanding principal amount). The Company has executed a supplemental indenture with U.S. Bank National Association, as Trustee, effectuating the proposed amendments to the Indenture, as described in the Offer to Purchase and Consent Solicitation Statement dated December 7, 2006. The Company has accepted for purchase all 9% Senior Notes validly tendered and not withdrawn prior to the Consent Payment Deadline and anticipates that payment for such 9% Senior Notes will be made on or about December 21, 2006. The 9% Senior Notes tendered may no longer be withdrawn and consents delivered may no longer be revoked.

The total consideration, excluding accrued and unpaid interest, for each $1,000 principal amount of 9% Senior Notes validly tendered (and not validly withdrawn) on or prior to the Consent Payment Deadline is $1,062.53, which includes a $20.00 consent payment. The total consideration was determined using a yield equal to a fixed spread of 50 basis points plus the bid side yield to maturity of the 3.625% U.S. Treasury Note due June 30, 2007, which yield was determined as of 2:00 p.m., New York City time, on December 20, 2006. Noteholders who validly tender their 9% Senior Notes will receive accrued and unpaid interest from the most recent interest payment date to, but not including, the applicable payment date.

The tender offer will expire at midnight, New York City time, on January 5, 2007, unless terminated or extended.

Wachovia Securities is acting as exclusive dealer manager and solicitation agent for the tender offer and the consent solicitation. The information agent and tender agent for the tender offer is D.F. King & Co., Inc. Questions regarding the tender offer and consent solicitation may be directed to Wachovia Securities' Liability Management Group, telephone number 866-309-6316 (toll free) and 704-715-8341 (call collect). Requests for copies of the Offer to Purchase and Consent Solicitation Statement and related documents may be directed to D.F. King & Co., Inc., telephone number 800-758-5378 (toll free) and 212-269-5550 (call collect).

This announcement is not an offer to purchase, a solicitation of an offer to sell, or a solicitation of consents with respect to the 9% Senior Notes. The tender offer and consent solicitation are made solely by means of the Offer to Purchase and Consent Solicitation Statement and the related Consent and Letter of Transmittal.

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/A, 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