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                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549


                                   FORM 8-K/A


                 Current Report Pursuant to Section 13 or 15(d)
                     of the Securities Exchange Act of 1934

         Date of Report (Date of earliest event reported): May 13, 1999

                          ORBITAL SCIENCES CORPORATION




                                                               
        DELAWARE                       0-18287                        06-1209561
(State of incorporation)       (Commission File Number)       (I.R.S. Employer I.D. No.)


                            21700 ATLANTIC BOULEVARD
                             DULLES, VIRGINIA 20166
                                 (703) 406-5000
                          (Address and telephone number
                         of principal executive offices)


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ITEM 4.  CHANGES IN REGISTRANT'S CERTIFYING ACCOUNTANT

         On May 13, 1999, Orbital Sciences Corporation ("Orbital" or the
"Company") received the response (the "Response Letter") of its former auditors,
KPMG LLP ("KPMG"), to the Company's Current Report on Form 8-K filed with the
Securities and Exchange Commission on April 29, 1999. The Response Letter, which
KPMG was required to deliver to the Company pursuant to Item 304(a)(3) of
Regulation S-K, is attached as Exhibit 16.1 hereto.

         The Company disagrees with a number of the statements made by KPMG in
its Response Letter. Of particular significance:

         -  The Company believes its Form 8-K correctly summarizes the
         Company's restatement of its quarterly financial statements for the
         first three quarters of 1998. The Company believed that its
         interpretation and application of accounting standards in its quarterly
         financial statements as originally filed were reasonable. Nevertheless,
         the Company accepted KPMG's interpretation of complex accounting 
         standards and agreed to the restatement proposed by KPMG.

         -  The Company believes that KPMG's characterizations and
         enumerations of the fourth quarter adjustments proposed in the course
         of its audit are unnecessary. Any audit involves adjustments proposed
         by an auditor that are then discussed with its client. Based on
         additional analyses of facts by the client and the auditor, the auditor
         may then modify its proposed adjustments or not. That was the process
         engaged in by Orbital and KPMG. What is significant is that (1) in
         Orbital's audited financial statements, all adjustments finally
         proposed by KPMG were recorded by the Company and (2) as indicated in
         KPMG's unqualified opinion, the Company's financial statements for the
         year ended December 31, 1998 complied with GAAP and contained all
         appropriate disclosures.

         -  The Company continues to disagree with KPMG's assertions 
         with respect to alleged material weaknesses. What is significant
         is that Orbital's new auditors, PricewaterhouseCoopers LLP
         ("PricewaterhouseCoopers"), have been given full authorization by the
         Company to speak with KPMG, and have done so. 


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                                   SIGNATURES

         Pursuant to the requirements of the Securities Exchange Act of 1934,
the registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                                        ORBITAL SCIENCES CORPORATION

Date:  May 14, 1999                     By: /s/  Jeffrey V. Pirone
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                                                 Jeffrey V. Pirone
                                                 Executive Vice President and
                                                     Chief Financial Officer


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                                    EXHIBITS

The following exhibit is filed as part of this report.

Exhibit No.                                   Description
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16.1                                          Letter regarding change in 
                                              certifying accountant