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                       SIXTH AMENDMENT TO NOTE AGREEMENT


    THIS SIXTH AMENDMENT to Note Agreement dated as of August 14, 1998 ("Sixth
Amendment") is entered into between Orbital Sciences Corporation, a Delaware
corporation (the "Company") and The Northwestern Mutual Life Insurance Company
(the "Purchaser").

                                R E C I T A L S:

    A.      The Company and the Purchaser have heretofore entered into the Note
Agreement dated as of June 1, 1995, the First Amendment to Note Agreement dated
as of June 30, 1995, the Second Amendment to Note Agreement dated as of March
15, 1996, the Third Amendment to Note Agreement dated as of July 31, 1996, the
Fourth Amendment to Note Agreement dated as of March 31, 1997, and the Fifth
Amendment to Note Agreement dated as of December 23, 1997 (as amended, the
"Note Agreement").

    B.      The Company and the Purchaser now desire to further amend,
effective on and as of August 14, 1998 (the "Effective Date"), certain of the
terms of the Note Agreement.

    C.      Capitalized terms used herein shall have the respective meanings
ascribed thereto in the Note Agreement unless herein defined or the context
shall otherwise require.

    D.      All requirements of law have been fully complied with and all other
acts and things necessary to make this Sixth Amendment a valid, legal and
binding instrument according to its terms for the purposes herein expressed
have been done or performed.

    NOW, THEREFORE, the Company and the Purchaser, for good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, do
hereby agree as follows:

    Section 1.       AMENDMENT.

    Section 1.1.  Section 8.1 of the Note Agreement shall be and is hereby
amended as follows:

           (a)      The definition of "Restricted Investments," Clause (h) is
   hereby amended by deleting the word "and" at the end thereof;

           (b)      The definition of "Restricted Investments," Clause (i) is
   hereby amended by substituting a semicolon for the period and adding the
   word "and" at the end thereof; and

           (c)      The definition of "Restricted Investment" is hereby amended
   by adding a new Clause (j) to read in its entirety as follows:
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                   (j)  Investments by the Company or any of its Subsidiaries
                   made on or after June 30, 1998 in an aggregate amount not
                   to exceed $50,000,000 and consisting of debt or shares of
                   capital stock of CCI International N.V., a company formed
                   and existing under the laws of the Netherlands Antilles.

     Section 2.    REPRESENTATIONS AND WARRANTIES OF THE COMPANY

     Section 2.1.  To induce the Purchaser to execute and deliver this
Sixth Amendment, the Company represents and warrants to the Purchaser (which
representations shall survive the execution and delivery of this Sixth
Amendment) that:

            (a)       this Sixth Amendment has been duly authorized, executed
     and delivered by it and constitutes the legal, valid and binding
     obligation, contract and agreement of the Company, enforceable against it
     in accordance with its terms, except as enforcement may be limited by
     bankruptcy, insolvency, reorganization, moratorium or similar laws or
     equitable principles relating to or limiting creditors' rights generally;

            (b)       the Note Agreement, as amended by this Sixth Amendment,
     constitutes the legal, valid and binding obligation, contract and
     agreement of the Company, enforceable against it in accordance with its
     terms, except as enforcement may be limited by bankruptcy, insolvency,
     reorganization, moratorium or similar laws or equitable principles
     relating to or limiting creditors' rights generally;

          (c)         the execution, delivery and performance by the Company of
     this Sixth Amendment (i) has been duly authorized by all requisite
     corporate action and, if required, shareholder action, (ii) does not
     require the consent or approval of any governmental or regulatory body or
     agency, and (iii) will not (A) violate (1) any provision of law, statute,
     rule or regulation or its certificate of incorporation or bylaws, (2) any
     order of any court or any rule, regulation or order of any other agency or
     government binding upon it, or (3) any provision of any material
     indenture, agreement or other instrument to which it is a party or by
     which its properties or assets are or may be bound, or (B) result in a
     breach or constitute (alone or with due notice or lapse of time or both) a
     default under any indenture, agreement or other instrument referred to in
     clause (iii)(A)(3) of this Section 2.1(c); and

          (d)         as of the date hereof and after giving effect to this
     Sixth Amendment, no Default or Event of Default has occurred which is
     continuing.

     Section 3.    CONDITIONS TO EFFECTIVENESS OF SIXTH AMENDMENT.

     Section 3.1.  This Sixth Amendment shall not become effective
until, and shall become effective when, each and every one of the following
conditions shall have been satisfied:

          (a)         executed counterparts of this Sixth Amendment, duly
     executed by the Company and the Purchaser, shall have been delivered to
     the Purchaser; and

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          (b)         the representations and warranties of the Company set
     forth in Section 2 hereof shall be true and correct on and with respect to
     the date hereof.

     Upon receipt of all of the foregoing, this Sixth Amendment shall on the
Effective Date become effective.

     Section 4.  MISCELLANEOUS.

     Section 4.1.  Except as modified and expressly amended by this Sixth
Amendment, the Note Agreement is in all respects ratified, confirmed and
approved and all of the terms, provisions and conditions hereof shall be and
remain in full force and effect.

     Section 4.2.  Any and all notices, requests, certificates and other
instruments executed and delivered after the execution and delivery of this
Sixth Amendment may refer to the Note Agreement without making specific
reference to this Sixth Amendment but nevertheless all such references shall
include this Sixth Amendment unless the context otherwise requires.

     Section 4.3.  This Sixth Amendment shall be governed by and construed in
accordance with the laws of the State of Illinois.

     Section 4.4.  This Sixth Amendment may be executed and delivered in any
number of counterparts, each of such counterparts constituting an original, but
all together only one Sixth Amendment.

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IN WITNESS WHEREOF, the Company and the Purchaser have caused this instrument
to be executed, all as of the day and year first above written.

                               ORBITAL SCIENCES CORPORATION


                               By:  /s/ Jeffrey V. Pirone
                                     Name:  Jeffrey V. Pirone
                                     Title:    Executive Vice President and
                                                Chief Financial Officer



                               Accepted and Agreed to:

                               THE NORTHWESTERN MUTUAL LIFE
                                  INSURANCE COMPANY


                               By: /s/  A Kipp Koester
                                     Name: A Kipp Koester
                                     Title:  Its Authorized Representative