UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 14A
Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 (Amendment No.     )
Filed by the Registrant  o
Filed by a Party other than the Registrant  o
Check the appropriate box:
o	Preliminary Proxy Statement
o	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))
o	Definitive Proxy Statement
o	Definitive Additional Materials
x	Soliciting Material under §240.14a-12
ORBITAL SCIENCES CORPORATION
(Name of Registrant as Specified In Its Charter)
(Name of Person(s) Filing Proxy Statement, if other than the Registrant)
Payment of Filing Fee (Check the appropriate box):
x	No fee required.
o	Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.
	(1)		Title of each class of securities to which transaction applies:
	(2)		Aggregate number of securities to which transaction applies:
	(3)		Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 0-11 (set forth the amount on which the filing fee is calculated and state how it was determined):
	(4)		Proposed maximum aggregate value of transaction:
	(5)		Total fee paid:
o	Fee paid previously with preliminary materials.
o	Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.
	(1)	Amount Previously Paid:
	(2)	Form, Schedule or Registration Statement No.:
	(3)	Filing Party:
	(4)	Date Filed:

The following letter was mailed to the Company’s suppliers on May 5, 2014:

Dear Valued Supplier,

On 29 April 2014, Orbital Sciences Corporation (NYSE: ORB) was pleased to announce that it has entered into a definitive agreement with Alliant Techsystems Inc. (NYSE: ATK), which will combine Orbital and ATK’s Aerospace and Defense Groups to create a leading global aerospace and defense systems company. The merger is conditioned on approval by the shareholders of both companies, the receipt of regulatory approvals, and other customary closing conditions. The transaction is expected to close by the end of 2014.

All current orders or data submitted to Orbital will continue to be covered under the existing terms and conditions or non-disclosure agreements before and after the merger.

You are an important part of Orbital’s team and we look forward to our continued partnership. Feel free to contact your supply chain representative should you have any questions.

Additional information on the merger can be found at Orbital’s website: http://www.orbital.com/.

Regards,

Stephanie Foster

Corporate Senior Vice President

Enterprise Supply Chain

* * * * *

Additional Information about the Proposed Transaction and Where to Find It

This communication relates to the proposed merger transaction pursuant to the terms of the Transaction Agreement, dated as of April 28, 2014, among Alliant Techsystems Inc. (“ATK”), Vista SpinCo Inc., Vista Merger Sub Inc. and Orbital Sciences Corporation (“Orbital”).

In connection with the proposed transaction, Orbital and ATK intend to file relevant materials with the SEC, including an ATK registration statement on Form S-4 that will include a joint proxy statement of Orbital and ATK and that also constitutes a prospectus of ATK.   INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS AND ANY OTHER RELEVANT DOCUMENTS WHEN THEY BECOME AVAILABLE, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT ORBITAL, ATK AND THE PROPOSED TRANSACTION.  The joint proxy statement/prospectus and other documents relating to the proposed transaction (when they are available) can be obtained free of charge at the SEC’s website at www.sec.gov.  These documents (when they are available) can also be obtained free of charge from Orbital upon written request to Orbital at investor.relations@orbital.com or by calling Barron Beneski at 703-406-5528 or from ATK upon written request to ATK by emailing investor.relations@atk.com or by calling Michael Pici at 703-412-3216.

Participants in the Solicitation

This communication is not a solicitation of a proxy from any investor or securityholder.  However, Orbital and ATK and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction under the rules of the SEC.  Information regarding Orbital’s directors and executive officers may be found in its Annual Report for the year ended December 31, 2013 on Form 10-K filed with the SEC on February 25, 2014 and the definitive proxy statement relating to its 2014 Annual Meeting of Stockholders filed with the SEC on March 11, 2014.  Information regarding ATK directors and executive officers may be found in its Annual Report for the year ended March 31, 2013 on Form 10-K filed with the SEC on May 23, 2013 and the definitive proxy statement relating to its 2013 Annual Meeting of Stockholders filed with the SEC on June 14, 2013.  These documents can be obtained free of charge from the sources indicated above.  Additional information regarding the interests of these participants will also be included in the joint proxy statement/prospectus when it becomes available

No Offer or Solicitation

This document shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.