EXHIBIT 5.1 March 31, 1997 Board of Directors Orion Network Systems, Inc. 2440 Research Boulevard, Suite 400 Rockville, Maryland 20850 Gentlemen: This firm has acted as counsel to Orion Network Systems, Inc. (the "Company"), a Delaware corporation, in connection with its registration, pursuant to a registration statement on Form S-8 filed on or about the date hereof (the "Registration Statement"), of 380,000 shares (the "Shares") of common stock, par value $.01 per share, of the Company, issuable under the Orion Network Systems, Inc. Non-Employee Director Stock Option Plan (the "Plan"). This letter is furnished to you pursuant to the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. ss. 229.601(b)(5), in connection with such registration. For purposes of this opinion letter, we have examined copies of the following documents: 1. An executed copy of the Registration Statement. 2. A copy of the Plan, as certified by the Secretary of the Company on the date hereof as then being complete, accurate and in effect. 3. The Restated Certificate of Incorporation of the Company, as amended (the "Charter"), as certified by the Secretary of State of the State of Delaware on January 29, 1997 and by the Secretary of the Company on the date hereof as then being complete, accurate and in effect. 4. The By-laws of the Company, as amended, as certified by the Secretary of the Company on the date hereof as then being complete, accurate and in effect. Board of Directors Orion Network Systems, Inc. March 31, 1997 Page 2 5. Resolutions and consents of the Board of Directors of the Company adopted on March 20, 1996 and March 12, 1997 as certified by the Secretary of the Company on the date hereof as then being complete, accurate and in effect relating to, among other things, approval of the Plan. We have not, except as specifically identified above, made any independent review or investigation of factual or other matters, including the organization, existence, good standing, assets, business or affairs of the Company or its subsidiaries. In our examination of the aforesaid certificates, records, and documents, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity, accuracy and completeness of all documents submitted to us as originals, and the authenticity, accuracy and completeness and conformity with the original documents of all documents submitted to us as certified, telecopied, photostatic, or reproduced copies. We have assumed the authenticity and accuracy of the foregoing certifications of corporate officers, on which we are relying, and have made no independent investigations thereof. This opinion is given in the context of the foregoing. This opinion letter is based as to matters of law solely on the General Corporation Law of the State of Delaware. We express no opinion herein as to any other laws, statutes, regulations, or ordinances. Based upon, subject to, and limited by the foregoing, we are of the opinion that the Shares, when issued and delivered in the manner and on the terms contemplated in the Registration Statement and the Plan (with the Company having received the consideration therefor, the form of which is in accordance with applicable law), will be validly issued, fully paid and non-assessable by the Company. We assume no obligation to advise you of any changes in the foregoing subsequent to the delivery of this opinion letter. This opinion letter has been prepared solely for your use in connection with the filing of the Registration Statement on the date of this letter, and should not be quoted in whole or in part or otherwise be referred to, nor be filed with or furnished to any governmental agency or other person or entity, without the prior written consent of this firm. Board of Directors Orion Network Systems, Inc. March 31, 1997 Page 3 We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement. In giving this consent, we do not thereby admit that we are an "expert" within the meaning of the Securities Act of 1933, as amended. Very truly yours, HOGAN & HARTSON L.L.P.