EXHIBIT 99.1


            WRITTEN STATEMENT OF CHAIRMAN AND CHIEF EXECUTIVE OFFICER
PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 (18 U.S.C. SECTION
                                     1350)


         The undersigned, the Chairman and Chief Executive Officer of Orbital
Sciences Corporation (the "Company"), hereby certifies that, to his knowledge,
on the date hereof:

         (a)      the Annual Report on Form 10-K/A of the Company for the Year
                  Ended December 31, 2001 filed on the date hereof with the
                  Securities and Exchange Commission (the "Report") fully
                  complies with the requirements of Section 13(a) or 15(d) of
                  the Securities Exchange Act of 1934; and

         (b)      information contained in the Report fairly presents, in all
                  material respects, the financial condition and results of
                  operations of the Company.



                                       /s/ David W. Thompson
                                       ---------------------------------------
                                       David W. Thompson
                                       Chairman and Chief Executive Officer
                                       February 21, 2003







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