<PAGE>   1
     As filed with the Securities and Exchange Commission on April 24, 2001
                                                       Registration No. 333-____
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                               ------------------
                                    FORM S-8

                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                          ORBITAL SCIENCES CORPORATION
             ------------------------------------------------------
             (Exact name of registrant as specified in its charter)

           DELAWARE                                      05-1209561
-----------------------------                ---------------------------------
 (State or other jurisdiction               (I.R.S. Employer Identification No.)
of incorporation or organization)

                            21700 ATLANTIC BOULEVARD
                             DULLES, VIRGINIA 20166
           ----------------------------------------------------------

                    (Address of principal executive offices)

            DEFERRED SALARY AND PROFIT SHARING PLAN FOR EMPLOYEES OF
                 ORBITAL SCIENCES CORPORATION (1998 RESTATEMENT)
                            (Full title of the plans)

                             LESLIE C. SEEMAN, ESQ.
             EXECUTIVE VICE PRESIDENT, GENERAL COUNSEL AND SECRETARY
                          ORBITAL SCIENCES CORPORATION
                            21700 ATLANTIC BOULEVARD
                             DULLES, VIRGINIA 20166
                                 (703) 406-5000
 -------------------------------------------------------------------------------
 (Name, address and telephone number, including area code, of agent for service)

                                    Copy to:
                              JAMES E. SHOWEN, ESQ.
                             HOGAN & HARTSON L.L.P.
                           555 THIRTEENTH STREET, N.W.
                           WASHINGTON, D.C. 20004-1109
                                 (202) 637-5600

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
==========================================================================================================
                                                    Proposed          Proposed maximum       Amount of
    Title of securities       Amount to be      maximum offering          aggregate        registration
     to be registered        registered (1)    price per share (2)    offering price (2)      fee (2)
----------------------------------------------------------------------------------------------------------
<S>                          <C>                  <C>               <C>                  <C>
  COMMON STOCK, PAR VALUE
           $.01                 1,500,000            $4.175            $6,262,500.00        $1,565.63
==========================================================================================================
</TABLE>

(1) Pursuant to Rule 416(c), this registration statement covers an indeterminate
amount of interests to be offered or sold pursuant to the Deferred Salary and
Profit Sharing Plan for Employees of Orbital Sciences Corporation (1998
Restatement).

(2) Estimated solely for the purpose of calculating the registration fee
pursuant to Rule 457 of the Securities Act of 1933, as amended, on the basis of
the average of the high and low prices per share of the Common Stock, par value
$0.01 per share, of Orbital Sciences Corporation, reported on the New York Stock
Exchange on April 20, 2001.



<PAGE>   2


                                EXPLANATORY NOTE

        This registration statement relates to stock to be granted under the
Deferred Salary and Profit Sharing Plan for Employees of Orbital Sciences
Corporation (1998 Restatement), as amended (the "Plan"), as described in a
registration statement on S-8, Registration No. 33-69887 (the "Prior
Registration Statement") and is filed solely to increase the number of shares of
Common Stock registered under the Plan from 500,000 shares to 2,000,000 shares.
The contents of the Prior Registration Statement, including all exhibits
thereto, are hereby incorporated by reference.


<PAGE>   3



                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 5.        Interests of Named Experts and Counsel.

                    Orbital Sciences Corporation (the "Company") has agreed to
hold KPMG LLP ("KPMG") harmless against and from any and all legal costs
and expenses incurred by KPMG in successful defense of any legal action or
proceeding that arises as a result of KPMG's consent to the incorporation by
reference of its audit reports on the Company's, ORBIMAGE's and ORBCOMM's past
consolidated financial statements incorporated by reference into this
registration statement.

ITEM 8.        EXHIBITS.

<TABLE>
<CAPTION>
             Exhibit
             Number  Description
             ------  -----------
           <S>       <C>
             5       Opinion of Hogan & Hartson L.L.P.*

             10      Deferred Salary and Profit Sharing Plan for Employees of
                     Orbital Sciences Corporation (1998 Restatement), as
                     amended (incorporated by reference to Exhibit 10.9 to
                     the company's Annual Report on Form 10-K for the fiscal
                     year ended December 31, 2000)

             23.1    Consent of Hogan & Hartson L.L.P. (contained in Exhibit 5)*


             23.2    Consent of PricewaterhouseCoopers LLP*

             23.3    Consent of KPMG LLP*

             23.4    Consent of Arthur Andersen LLP*

             24      Power of Attorney (contained on the Signature Pages)*
</TABLE>

-----------

* Filed herewith.



                                       2
<PAGE>   4


                                   SIGNATURES

        Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the County of Loudoun, the Commonwealth of Virginia on the 24th
day of April, 2001.

                            ORBITAL SCIENCES CORPORATION



                            BY:  /s/ David W. Thompson
                                 ------------------------------------------
                                 David W. Thompson, Chairman of the Board
                                 and Chief Executive Officer




                                POWER OF ATTORNEY

             Each person whose signature appears below constitutes and appoints
David W. Thompson and Leslie C. Seeman, or any of them, their true and lawful
attorneys-in-fact and agents, with full power of substitution and capacities,
for then and in their name, place and stead, in any and all capacities, to sign
any amendments (including post-effective amendments) to this Registration
Statement, and to file the same, with all exhibits thereto, and other documents
in connection therewith, with the Securities and Exchange Commission, granting
unto said attorneys-in-fact an agents full power and authority to perform each
and every act and thing requisite and necessary to be done in and about the
premises, as fully to all intents and purposes as they might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents, or their substitute or substitutes, may lawfully do or cause to be done
by virtue hereof.

             Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below on April 24, 2001 by the following
persons in the capacities indicated.



                       SIGNATURE:                          TITLE:
               ------------------------       ----------------------------------

               /s/ DAVID W. THOMPSON
               ------------------------       Chairman of the Board, Chief
               DAVID W. THOMPSON              Executive Officer and Director

               /s/ JAMES R. THOMPSON
               ------------------------       President, Chief Operating
               JAMES R. THOMPSON              Officer and Director

               /s/ GARRETT E. PIERCE
               ------------------------       Executive Vice President, Chief
               GARRETT E. PIERCE              Financial Officer and Director

               /s/ HOLLIS M. THOMPSON
               ------------------------       Vice President and Controller
               HOLLIS M. THOMPSON


                                       3
<PAGE>   5

               ------------------------       Director
               FRED C. ALCORN

               /s/ KELLY H. BURKE
               ------------------------       Director
               KELLY H. BURKE

               /s/ BRUCE W. FERGUSON
               ------------------------       Director
               BRUCE W. FERGUSON

               /s/ DANIEL J. FINK
               ------------------------       Director
               DANIEL J. FINK

               /s/ LENNARD A. FISK
               ------------------------       Director
               LENNARD A. FISK

               /s/ JACK L. KERREBROCK
               ------------------------       Director
               JACK L. KERREBROCK

               /s/ DOUGLAS S. LUKE
               ------------------------       Director
               DOUGLAS S. LUKE

               /s/ JANICE I. OBUCHOWSKI
               ------------------------       Director
               JANICE I. OBUCHOWSKI

               /s/ FRANK L. SALIZZONI
               ------------------------       Director
               FRANK L. SALIZZONI

               /s/ HARRISON H. SCHMITT
               ------------------------       Director
               HARRISON H. SCHMITT

               /s/ SCOTT L. WEBSTER
               ------------------------       Director
               SCOTT L. WEBSTER



                                       4
<PAGE>   6


                                  EXHIBIT INDEX



<TABLE>
<CAPTION>
Exhibit
Number                                    Description                                   Page
------                                    -----------                                   ----
<S>          <C>                                                                      <C>
5            Opinion of Hogan & Hartson L.L.P.*

10           Orbital Sciences Corporation 1997 Stock Option and Incentive Plan,
             as amended (incorporated by reference to Exhibit 10.9 to the
             company's Annual Report on Form 10-K for the fiscal year ended
             December 31,
             2000)

23.1         Consent of Hogan & Hartson L.L.P. (contained in Exhibit 5)*

23.2         Consent of PricewaterhouseCoopers LLP*

23.3         Consent of KPMG LLP*

23.4         Consent of Arthur Andersen LLP*

24           Power of Attorney (contained on the Signature Pages)*
</TABLE>

------------

* Filed herewith.


                                       5
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{"company-data": {"conformed-name": "ORBITAL SCIENCES CORP /DE/", "cik": "0000820736", "assigned-sic": "3812", "irs-number": "061209561", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-59474", "film-number": "1609907"}, "business-address": {"street1": "21700 ATLANTIC BLVD", "city": "DULLES", "state": "VA", "zip": "20166", "phone": "7034065000"}, "mail-address": {"street1": "21700 ATLANTIC BLVD", "street2": "21700 ATLANTIC BLVD", "city": "DULLES", "state": "VA", "zip": "20166"}, "former-company": {"former-conformed-name": "ORBITAL SCIENCES CORP II", "date-changed": "19900212"}}
1
     As filed with the Securities and Exchange Commission on April 24, 2001
                                                       Registration No. 333-____
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                               ------------------
                                    FORM S-8

                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                          ORBITAL SCIENCES CORPORATION
             ------------------------------------------------------
             (Exact name of registrant as specified in its charter)

           DELAWARE                                      05-1209561
-----------------------------                ---------------------------------
 (State or other jurisdiction               (I.R.S. Employer Identification No.)
of incorporation or organization)

                            21700 ATLANTIC BOULEVARD
                             DULLES, VIRGINIA 20166
           ----------------------------------------------------------

                    (Address of principal executive offices)

            DEFERRED SALARY AND PROFIT SHARING PLAN FOR EMPLOYEES OF
                 ORBITAL SCIENCES CORPORATION (1998 RESTATEMENT)
                            (Full title of the plans)

                             LESLIE C. SEEMAN, ESQ.
             EXECUTIVE VICE PRESIDENT, GENERAL COUNSEL AND SECRETARY
                          ORBITAL SCIENCES CORPORATION
                            21700 ATLANTIC BOULEVARD
                             DULLES, VIRGINIA 20166
                                 (703) 406-5000
 -------------------------------------------------------------------------------
 (Name, address and telephone number, including area code, of agent for service)

                                    Copy to:
                              JAMES E. SHOWEN, ESQ.
                             HOGAN & HARTSON L.L.P.
                           555 THIRTEENTH STREET, N.W.
                           WASHINGTON, D.C. 20004-1109
                                 (202) 637-5600

                         CALCULATION OF REGISTRATION FEE
==========================================================================================================
                                                    Proposed          Proposed maximum       Amount of
    Title of securities       Amount to be      maximum offering          aggregate        registration
     to be registered        registered (1)    price per share (2)    offering price (2)      fee (2)
----------------------------------------------------------------------------------------------------------
COMMON STOCK, PAR VALUE
           $.01                 1,500,000            $4.175            $6,262,500.00        $1,565.63
==========================================================================================================
(1) Pursuant to Rule 416(c), this registration statement covers an indeterminate
amount of interests to be offered or sold pursuant to the Deferred Salary and
Profit Sharing Plan for Employees of Orbital Sciences Corporation (1998
Restatement).

(2) Estimated solely for the purpose of calculating the registration fee
pursuant to Rule 457 of the Securities Act of 1933, as amended, on the basis of
the average of the high and low prices per share of the Common Stock, par value
$0.01 per share, of Orbital Sciences Corporation, reported on the New York Stock
Exchange on April 20, 2001.
2

                                EXPLANATORY NOTE

        This registration statement relates to stock to be granted under the
Deferred Salary and Profit Sharing Plan for Employees of Orbital Sciences
Corporation (1998 Restatement), as amended (the "Plan"), as described in a
registration statement on S-8, Registration No. 33-69887 (the "Prior
Registration Statement") and is filed solely to increase the number of shares of
Common Stock registered under the Plan from 500,000 shares to 2,000,000 shares.
The contents of the Prior Registration Statement, including all exhibits
thereto, are hereby incorporated by reference.
3

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 5.        Interests of Named Experts and Counsel.

                    Orbital Sciences Corporation (the "Company") has agreed to
hold KPMG LLP ("KPMG") harmless against and from any and all legal costs
and expenses incurred by KPMG in successful defense of any legal action or
proceeding that arises as a result of KPMG's consent to the incorporation by
reference of its audit reports on the Company's, ORBIMAGE's and ORBCOMM's past
consolidated financial statements incorporated by reference into this
registration statement.

ITEM 8.        EXHIBITS.
Exhibit
             Number  Description
             ------  -----------
5       Opinion of Hogan & Hartson L.L.P.*

             10      Deferred Salary and Profit Sharing Plan for Employees of
                     Orbital Sciences Corporation (1998 Restatement), as
                     amended (incorporated by reference to Exhibit 10.9 to
                     the company's Annual Report on Form 10-K for the fiscal
                     year ended December 31, 2000)

             23.1    Consent of Hogan & Hartson L.L.P. (contained in Exhibit 5)*

             23.2    Consent of PricewaterhouseCoopers LLP*

             23.3    Consent of KPMG LLP*

             23.4    Consent of Arthur Andersen LLP*

             24      Power of Attorney (contained on the Signature Pages)*
-----------

* Filed herewith.

                                       2
4

                                   SIGNATURES

        Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the County of Loudoun, the Commonwealth of Virginia on the 24th
day of April, 2001.

                            ORBITAL SCIENCES CORPORATION

                            BY:  /s/ David W. Thompson
                                 ------------------------------------------
                                 David W. Thompson, Chairman of the Board
                                 and Chief Executive Officer

                                POWER OF ATTORNEY

             Each person whose signature appears below constitutes and appoints
David W. Thompson and Leslie C. Seeman, or any of them, their true and lawful
attorneys-in-fact and agents, with full power of substitution and capacities,
for then and in their name, place and stead, in any and all capacities, to sign
any amendments (including post-effective amendments) to this Registration
Statement, and to file the same, with all exhibits thereto, and other documents
in connection therewith, with the Securities and Exchange Commission, granting
unto said attorneys-in-fact an agents full power and authority to perform each
and every act and thing requisite and necessary to be done in and about the
premises, as fully to all intents and purposes as they might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents, or their substitute or substitutes, may lawfully do or cause to be done
by virtue hereof.

             Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below on April 24, 2001 by the following
persons in the capacities indicated.

                       SIGNATURE:                          TITLE:
               ------------------------       ----------------------------------

               /s/ DAVID W. THOMPSON
               ------------------------       Chairman of the Board, Chief
               DAVID W. THOMPSON              Executive Officer and Director

               /s/ JAMES R. THOMPSON
               ------------------------       President, Chief Operating
               JAMES R. THOMPSON              Officer and Director

               /s/ GARRETT E. PIERCE
               ------------------------       Executive Vice President, Chief
               GARRETT E. PIERCE              Financial Officer and Director

               /s/ HOLLIS M. THOMPSON
               ------------------------       Vice President and Controller
               HOLLIS M. THOMPSON

                                       3
5

               ------------------------       Director
               FRED C. ALCORN

               /s/ KELLY H. BURKE
               ------------------------       Director
               KELLY H. BURKE

               /s/ BRUCE W. FERGUSON
               ------------------------       Director
               BRUCE W. FERGUSON

               /s/ DANIEL J. FINK
               ------------------------       Director
               DANIEL J. FINK

               /s/ LENNARD A. FISK
               ------------------------       Director
               LENNARD A. FISK

               /s/ JACK L. KERREBROCK
               ------------------------       Director
               JACK L. KERREBROCK

               /s/ DOUGLAS S. LUKE
               ------------------------       Director
               DOUGLAS S. LUKE

               /s/ JANICE I. OBUCHOWSKI
               ------------------------       Director
               JANICE I. OBUCHOWSKI

               /s/ FRANK L. SALIZZONI
               ------------------------       Director
               FRANK L. SALIZZONI

               /s/ HARRISON H. SCHMITT
               ------------------------       Director
               HARRISON H. SCHMITT

               /s/ SCOTT L. WEBSTER
               ------------------------       Director
               SCOTT L. WEBSTER

                                       4
6

                                  EXHIBIT INDEX
Exhibit
Number                                    Description                                   Page
------                                    -----------                                   ----
5            Opinion of Hogan & Hartson L.L.P.*

10           Orbital Sciences Corporation 1997 Stock Option and Incentive Plan,
             as amended (incorporated by reference to Exhibit 10.9 to the
             company's Annual Report on Form 10-K for the fiscal year ended
             December 31,
             2000)

23.1         Consent of Hogan & Hartson L.L.P. (contained in Exhibit 5)*

23.2         Consent of PricewaterhouseCoopers LLP*

23.3         Consent of KPMG LLP*

23.4         Consent of Arthur Andersen LLP*

24           Power of Attorney (contained on the Signature Pages)*
------------

* Filed herewith.

                                       5