EXHIBIT 5


                       [HOGAN & HARTSON L.L.P. LETTERHEAD]





                                  May 13, 2002



Board of Directors
Orbital Sciences Corporation
21839 Atlantic Boulevard
Dulles, Virginia  20166

Ladies and Gentlemen:

                  We are acting as counsel to Orbital Sciences Corporation, a
Delaware corporation (the "COMPANY"), in connection with its registration
statement on Form S-8, as amended (the "REGISTRATION STATEMENT"), filed with the
Securities and Exchange Commission relating to the registration of 1,000,000
shares of the Company's common stock, par value $.01 per share (the "SHARES"),
issued from time to time pursuant to the Orbital Sciences Corporation 1999
Employee Stock Purchase Plan, as amended (the "PLAN"). This opinion letter is
furnished to you at your request to enable you to fulfill the requirements of
Item 601(b)(5) of Regulation S-K, 17 C.F.R. Section 229.601(b)(5), in connection
with the Registration Statement.

                  For purposes of this opinion letter, we have examined copies
of the following documents:

1.       An executed copy of the Registration Statement.

2.       The Restated Certificate of Incorporation of the Company, as amended,
         as certified by the Secretary of the State of the State of Delaware on
         May 8, 2002 and by an Assistant Secretary of the Company on the date
         hereof as being complete, accurate, and in effect.

3.       The Amended and Restated Bylaws of the Company, as certified by an
         Assistant Secretary of the Company on the date hereof as being
         complete, accurate, and in effect.

4.       Resolutions of the Board of Directors of the Company adopted at
         meetings held on October 22, 1998 and January 24, 2002, as certified by
         an Assistant Secretary of the Company on the date hereof as being
         complete, accurate, and in effect, relating to the approval of the Plan
         and arrangements in connection therewith.

5.       The Plan.

                  In our examination of the aforesaid documents, we have assumed
the genuineness of all signatures, the legal capacity of all natural persons,
the accuracy and completeness of all documents submitted to us, the authenticity
of all original documents, and the conformity to





Board of Directors
Orbital Sciences Corporation
May 13, 2002
Page 2



authentic original documents of all documents submitted to us as copies
(including telecopies). This opinion letter is given, and all statements herein
are made, in the context of the foregoing.

                  This opinion letter is based as to matters of law solely on
the Delaware General Corporation Law, as amended. We express no opinion herein
as to any other laws, statutes, ordinances, rules, or regulations. As used
herein, the term "Delaware General Corporation Law, as amended" includes the
statutory provisions contained therein, all applicable provisions of the
Delaware Constitution and reported judicial decisions interpreting these laws.

                  Based upon, subject to and limited by the foregoing, we are of
the opinion that following the issuance of the Shares by the Company pursuant to
the Plan, the Shares will be validly issued, fully paid and nonassessable.

                  This opinion letter has been prepared for your use in
connection with the Registration Statement and speaks as of the date hereof. We
assume no obligation to advise you of any changes in the foregoing subsequent to
the delivery of this opinion letter.

                  We hereby consent to the filing of this opinion letter as
Exhibit 5 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,


                                            /s/ Hogan & Hartson L.L.P.

                                            HOGAN & HARTSON L.L.P.







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