of a cash tender offer (the “Tender Offer”) for any and all of Orbital Sciences Corporation’s (NYSE: ORB) $143.75 million aggregate principal amount of its outstanding 2.4375 percent Convertible Senior Subordinated Notes due 2027 (the “Convertible Notes”). The Tender Offer will expire at 12:00 midnight, New York City time, on December 18, 2012, unless extended (as such time and date may be extended, the “Expiration Date”) or terminated earlier by the Company in its sole discretion.

Convertible Notes tendered may be withdrawn at any time prior to 12:00 midnight, New York City time, on the Expiration Date. The Tender Offer is not subject to any minimum tender condition, however, the Tender Offer is subject to a financing condition (as described below), as well as certain other customary conditions.

Upon the terms and subject to the conditions set forth in the Offer to Purchase, dated the date hereof (the “Offer to Purchase”), and Letter of Transmittal, dated the date hereof (the “Letter of Transmittal”), the Company is offering to pay, in cash, $1,015 for each $1,000 principal amount of Convertible Notes that are validly tendered and not properly withdrawn prior to 12:00 midnight, New York City time, on the Expiration Date and acquired pursuant to the Tender Offer. In addition, the Company will pay accrued and unpaid interest on Convertible Notes that are accepted for purchase in the Tender Offer up to, but excluding, the settlement date of the Tender Offer. The Company intends to fund the repurchase of the Convertible Notes using the net proceeds of a proposed new term loan, together with cash on hand (as necessary). The timing, terms and size of the proposed term loan are subject to market and other conditions, and the Company cannot provide any assurance that the proposed term loan will be consummated at any specific time, or at all. The Tender Offer is conditioned upon the consummation of the proposed term loan, on terms satisfactory to the Company, in an aggregate principal amount of at least $150 million.

Subject to applicable law, the Company may, in its sole discretion, waive conditions applicable to the Tender Offer or extend, terminate or otherwise amend the Tender Offer.

The complete terms and conditions of the Tender Offer are set forth in the Offer to Purchase and Letter of Transmittal and the other related materials that the Company will distribute to holders of Convertible Notes after these documents are filed with the Securities and Exchange Commission (the “Commission”) as exhibits to the Company’s Schedule TO. Holders of Convertible Notes should read the Offer to Purchase and Letter of Transmittal and the other related materials because they contain important information including various terms and conditions of the Tender Offer.

Citigroup Global Markets Inc. and Wells Fargo Securities, LLC are the dealer managers for the Tender Offer. Questions regarding the Tender Offer may be directed to Citigroup Global Markets Inc. and Wells Fargo Securities, LLC at (800) 558-3745 (U.S. toll free).

Requests for documents may be directed to Georgeson Inc., the information agent, at (888) 658-5755 (U.S. toll free) or at 212-440-9800 (collect), or in writing to Georgeson Inc., 199 Water Street, 26th Floor, New York, NY 10038. None of the Company, its board of directors (or any committee thereof), the dealer managers, the depositary, the information agent, the trustee for the Convertible Notes or their respective affiliates is making any recommendation as to whether or not holders should tender all or any portion of their Convertible Notes in the Tender Offer.