PERFORMANCE SHARE AGREEMENT


         This Performance Share Agreement (the "Agreement") is made as of the
9th day of August 2000 by and between Orbital Sciences Corporation, a Delaware
corporation (the "Company"), and Garrett E. Pierce (the "Executive").

         WHEREAS, the Human Resources and Nominating Committee of the Board of
Directors of the Company (the "Committee") has determined that it is desirable
and in the best interests of the Company to grant to the Executive the right
to receive performance share units (the "Performance Shares"), in order to
provide the Executive with further incentive to enhance the profitability and
financial strength of the Company by linking a component of the Executive's
compensation to Company stock value, which Performance Shares entitle the
Executive to receive an annual bonus measured by the increased value of the
Company's common stock, par value $.01 per share (the "Common Stock").

         NOW THEREFORE, in consideration of the mutual promises and covenants
contained herein, the parties hereby agree as follows:

         1.       GRANT OF PERFORMANCE SHARES.  The Company hereby grants to
the Executive a total of 50,000 Performance Shares, which shall have the
features set forth below.  The date of the grant of the Performance Shares is
August 9, 2000.

                  a.       Vesting.  The 50,000 Performance Shares shall vest
                           immediately.

                  b.       Performance Bonus Calculation. Until expiration or
                           termination, each vested Performance Share shall
                           entitle the Executive to receive a bonus (the
                           "Performance Bonus"). The Performance Bonus shall
                           be calculated on each of August 9, 2001 and 2002
                           with respect to the aggregate number of Performance
                           Shares that have vested as of August 1 of such
                           year. The Performance Bonus shall be equal to the
                           increase, if any, from the Base Price to the
                           Anniversary Valuation Price, as illustrated below
                           for each applicable valuation period.


<TABLE>
<CAPTION>
         NUMBER OF                                                                      ANNIVERSARY
         ---------                                                                      -----------
         PERFORMANCE SHARES         BASE DATE                 BASE PRICE                VALUATION PRICE
         ------------------         ---------                 ----------                ---------------
<S>                                 <C>                       <C>                       <C>
         50,000                     August 9, 2000            Fair Market Value         Fair Market Value
                                                              on August 9, 2000         on August 9, 2001

         50,000                     August 9, 2001            Fair Market Value         Fair Market Value
                                                              on August 9, 2001         on August 9, 2002
</TABLE>

<PAGE>   2


                 c.        Payment of Performance Bonus. The Performance Bonus,
                           if any, shall be paid in cash in the form of a credit
                           to the Executive's account under the Company's 1995
                           Deferred Compensation Plan. Such payment shall be
                           made as soon as practicable after calculation of the
                           Performance Bonus. Fifty percent (50%) of such credit
                           shall vest immediately, with the other Fifty percent
                           (50%) vesting on August 9 of the subsequent year.

                  d.       Expiration.  The Performance Shares shall expire on
                           August 10, 2002 unless this Agreement is terminated
                           according to its terms at an earlier time.

                  e.       Fair Market Value. For purposes of this Agreement,
                           the Fair Market Value shall be equal to the average
                           closing sales price of the Common Stock on the
                           national securities exchange on which the Common
                           stock is then principally traded, calculated for
                           the 20 trading days immediately preceding August 9
                           of the applicable valuation year.

         2.       LIMITATION ON TRANSFER. The Performance Shares are not
transferable by the Executive.

         3.       PERFORMANCE SHARE ADJUSTMENTS.

                  a.       Changes in Stock.  If the outstanding shares of
                           Common Stock of the Company are increased,
                           decreased, changed into or exchanged for a
                           different number or kind of shares of the Company
                           through reorganization, recapitalization,
                           reclassification, stock dividend, stock split or
                           reverse stock split, upon authorization of the
                           Board, a proportionate adjustment shall be made in
                           the number or kind of Common Stock subject to the
                           Performance Shares, so that the proportionate
                           interest of the Executive immediately following
                           such event shall, to the extent practicable, be the
                           same as immediately prior to such event.  Any such
                           adjustment to Performance Shares shall include a
                           corresponding proportionate adjustment in the Base
                           Price per share of Common Stock.

                  b.       Reorganization in Which the Company is the
                           Surviving Corporation.  Subject to subparagraph (c)
                           below, if the Company shall be the surviving
                           corporation in any reorganization, merger or
                           consolidation of the Company with one or more other
                           corporations, the Performance Shares shall pertain
                           to and apply to the securities to which a holder of
                           the number of shares of Common Stock subject to the
                           Performance Shares would have been entitled
                           immediately following such reorganization, merger
                           or consolidation, with a corresponding
                           proportionate adjustment in the Base Price per
                           share of Common Stock so that the aggregate Base
                           Price thereafter shall be the same as the aggregate
                           Base Price of the Common Stock remaining subject to
                           the Performance Shares immediately prior to such
                           reorganization, merger or consolidation.

<PAGE>   3

                  c.       Reorganization in Which the Company is Not the
                           Surviving Corporation or Sale of Assets or Stock.
                           Upon the dissolution or liquidation of the Company,
                           or upon a merger, consolidation or reorganization
                           of the Company with one or more other corporations
                           in which the Company is not the surviving
                           corporation, or upon a sale of substantially all
                           the assets of the Company to another corporation,
                           or upon any transaction (including, without
                           limitation, a merger or reorganization in which the
                           Company is the surviving corporation) approved by
                           the Board which results in any person or entity
                           owning Eighty percent (80%) or more of the combined
                           voting power of all classes of the stock of the
                           Company, unless provision is made in writing in
                           connection with such transaction for the assumption
                           of this Agreement with such adjustments as the
                           Board deems appropriate with respect to the
                           features, terms and conditions of the Performance
                           Shares, the Performance Shares hereunder shall
                           immediately entitle the Executive to a Performance
                           Bonus in an amount equal to the difference between
                           the applicable Base Price and the Fair Market Value
                           of the per share Common Stock on the trading date
                           immediately preceding the closing date of such
                           Transaction, and any unpaid portion of a previously
                           vested Performance Bonus shall be immediately paid.

                  d.       Adjustments.  In all cases, the nature and extent
                           of adjustments under this Section 3 shall be
                           determined by the Committee in its sole discretion,
                           and any such determination as to what adjustments
                           shall be made, and the extent thereof, shall be
                           final and binding.

         4.       WITHHOLDING OF TAXES. The parties hereto recognize that the
Company may be obligated to withhold federal, state and local income taxes and
Social Security taxes to the extent that the Executive realizes ordinary
income in connection with receipt of the Performance Bonus pursuant to this
Agreement. The Executive agrees that the Company may withhold amounts needed
to cover such taxes from payments otherwise due and owing to the Executive.

         5.       DISCLAIMER OF RIGHTS. No provision in this Agreement shall
be construed to confer upon the Executive the right to be employed by the
Company, or to interfere in any way with the right and authority of the
Company either to increase or decrease the compensation of the Executive at
any time, or to terminate any employment or other relationship between the
Executive and the Company.

         6.       INTERPRETATION OF PERFORMANCE SHARE AGREEMENT.  All
decisions and interpretations made by the Committee or the Board of Directors
of the Company with regard to any questions arising under this Agreement shall
be binding and conclusive on the Company and the Executive.

         7.       TERMINATION. Except as otherwise provided herein, this
Agreement shall terminate and all rights and obligations of the parties
hereunder shall be void and of no effect immediately upon the date the
Executive ceases to hold the same, equivalent or higher grade

<PAGE>   4

office as that office set forth in the first paragraph of this Agreement or
August 9, 2003, whichever occurs first. For purposes of this Agreement, an
approved leave of absence shall not be deemed an event resulting in the
Executive ceasing to hold such office under this Agreement. An approved leave
of absence shall mean an absence approved by the Committee for military leave,
sick leave, or other bona fide leave, as long as the Executive's right to
re-employment is guaranteed by contract, statute or the policy of the Company.

8.       MISCELLANEOUS

         a.       Title and Headings.  Titles and headings of sections of the
                  Agreement are for convenience of reference only and shall
                  not affect the construction of any provision of this
                  Agreement.

         b.       Governing Law.  This Agreement shall be governed by,
                  interpreted under and construed and enforced in accordance
                  with the internal laws, and not the laws pertaining to
                  conflicts or choice of laws, of the State of Delaware.


                  IN WITNESS WHEREOF, the parties have executed this agreement
as of August 9, 2000.


ORBITAL SCIENCES CORPORATION


By:   /s/ David W. Thompson                       /s/ Garrett E. Pierce
      --------------------------------            ---------------------------
      David W. Thomspon                           Garrett E. Pierce
      Chairman and Chief Executive Officer

Source: OneCLE Business Contracts.