Document:

<PAGE>   1
August 2, 2000

Mr. Jeffrey V. Pirone
6418 Tilden Lane
N. Bethesda, Maryland  20852

Dear Jeff:

As we discussed, this letter agreement (the "Agreement") reflects the terms of
your employment at Orbital Sciences Corporation ("Orbital") effective July 21,
2000. All necessary consents and approvals required of Orbital to enter into
this Agreement have been obtained.

1.       Employment

         Effective July 21, 2000, you agree to resign from your position as
         Executive Vice President and Chief Financial Officer of Orbital and
         as a director and/or officer of Orbital and each of its subsidiaries
         and affiliates where you hold such a position. From July 21, 2000
         through the earlier of (i) July 21, 2002, or (ii) such date that you
         accept a full-time position with another employer (such earlier date,
         the "Employment Termination Date"), you will remain employed by
         Orbital as Vice President, Special Projects, reporting to the Chief
         Executive Officer. In such capacity, you agree to make yourself
         reasonably available to provide reasonable assistance on an ad hoc
         part-time basis on such matters relating to Orbital's business as
         shall be reasonably requested by the Chief Executive Officer. In
         addition, you agree to make yourself reasonably available to provide
         reasonable assistance in order to support the transition of your
         duties, responsibilities, current assignments and projects to your
         successor. You agree to provide prompt written notice to Orbital of
         your acceptance of a full-time position with another employer within
         three business days of acceptance of such employment.

         In addition, you agree to make yourself reasonably available and to
         reasonably cooperate with Orbital in any litigation, investigation,
         action, suit or claim of whatever nature that may be brought by or
         against Orbital, its subsidiaries, affiliates, officers, directors or
         employees relating to or arising in connection with matters with
         which you were involved or of which you had knowledge during your
         employment with Orbital. After your Employment Termination Date, such
         availability and cooperation shall be subject to reasonable
         accommodation for the requirements of your new position. You shall
         not conduct any activities on behalf of Orbital or hold yourself out
         as representing Orbital except at the direction of the Chief
         Executive Officer.

<PAGE>   2

Jeffrey V. Pirone
August 2, 2000
Page Two

2.       Compensation

         Orbital agrees to pay you your full base salary through July 21,
         2000. Any unpaid salary through such date shall be paid by direct
         deposit into your account no later than August 4, 2000. In lieu of
         any further salary payments to you after that date and as severance
         compensation for your past performance, Orbital agrees to pay you on
         or before August 10, 2000 by wire transfer in accordance with wiring
         instructions provided by you, a one-time cash payment of $731,000,
         which is equal to two (2) times your annual base salary of $295,000,
         plus 80% of your targeted annual incentive bonus for 2000.

         In addition, you shall be entitled to receive no more than three (3)
         non-discretionary cash bonuses in the amount of $75,000 each upon the
         successful consummation, to occur no later than December 31, 2000, of
         the following currently contemplated transactions: (i) Fairchild
         Defense divestiture, (ii) sale of Magellan Corporation and
         monetization of proceeds, and (iii) third party equity investment of
         at least $100 million in ORBCOMM or through Orbital with proceeds
         directed to ORBCOMM . Orbital shall pay you the cash bonus within
         fifteen (15) days following the closing of each transaction.

3.       Administrative Arrangement

         Orbital agrees to provide you reasonable administrative and
         secretarial support, including use of voice-mail and e-mail, through
         the Employment Termination Date.

4.       Benefits

         You shall be entitled to continue to participate in all employee
         health and welfare benefit plans in accordance with their terms
         through the Employment Termination Date. Thereafter, you may elect to
         continue coverage under COBRA at your expense.

5.       Retirement Plans

         You shall continue to be entitled to receive all benefits that may be
         due you under each of (1) the Orbital Deferred Salary & Profit
         Sharing Plan (the "Orbital 401(k)"), and (2) the Orbital 1995
         Deferred Compensation Plan (the "Deferred Compensation Plan"), in
         each case in accordance with the terms of such plans. Subsequent to
         the Employment Termination Date, Orbital shall pay out the balance of
         your account in the Deferred Compensation Plan pursuant to your
         election under such plan and shall comply with your election with
         respect to your balance in the Orbital 401(k) in accordance with such
         plan.

                                      2

<PAGE>   3

Jeffrey V. Pirone
August 2, 2000
Page Three

6.       Leave

         As of July 21, 2000, you will no longer accrue any leave under
         Orbital's composite leave policy. On August 4, 2000, you shall be
         paid by direct deposit in your account a lump sum payment for your
         hours of accrued but unused composite leave at your current salary
         rate through July 21, 2000.

7.       Stock Options, ESPP and Promissory Note

         Except as provided below, your stock options in Orbital shall vest
         immediately and you shall be entitled to exercise any or all stock
         options for a period of two (2) years from July 21, 2000, provided,
         however, that you agree to the substitution of nonstatutory stock
         options for incentive stock options to the extent necessary to
         implement the foregoing, and provided further that such exercise is
         permitted under Orbital's insider trading policy. Notwithstanding the
         foregoing, the 150,000 Orbital stock options granted to you on May
         28, 1999 shall be cancelled as of the date of this Agreement. Your
         stock options in any Orbital subsidiaries or affiliates shall
         continue to vest until your Employment Termination Date. Upon your
         Employment Termination Date, all subsidiary or affiliate options that
         are not exercisable shall terminate and options that are exercisable
         on such date shall be exercisable and expire in accordance with their
         terms.

         You shall be eligible to continue to participate in the Orbital
         Employee Stock Purchase Plan for the year ended December 31, 2000.
         Thereafter, your eligibility to participate shall terminate.

         The Promissory Note dated May 1, 1998 in the amount of $50,000
         payable to the order of Orbital shall be terminated and discharged by
         Orbital and Orbital shall surrender the original note marked "Paid
         and Cancelled." You shall assume full responsibility for the payment
         of any tax liability for federal and state taxes on amounts forgiven
         and discharged.

8.       Taxes

         All payments to be made to you by Orbital, including payments under
         paragraph 2, shall be made net of any federal, state and local taxes,
         FICA or other amounts required to be withheld by Orbital.

9.       Expense Reimbursement

         You shall be reimbursed for normal business expenses incurred prior
         to your Employment Termination Date, in accordance with Orbital's
         normal expense reimbursement policy.

                                      3

<PAGE>   4

Jeffrey V. Pirone
August 2, 2000
Page Four

10.      Release

         Except as provided in this Agreement, you hereby release, acquit and
         forever discharge Orbital, its subsidiaries, affiliates, successors,
         officers, directors and employees, the Deferred Compensation Plan and
         the Orbital 401(k) (collectively, the "Orbital Entities") of and
         from, and hereby waive all rights with respect to, any and all
         rights, actions, suits, claims, causes of actions, damages, expenses
         or costs of whatever nature arising out of or related to (i)
         Orbital's employment of you, including but not limited to the
         Executive Employment Agreement between you and Orbital dated as of
         October 21, 1998, and any and all other contracts and agreements,
         whether oral or in writing, relating to such employment, (ii) the
         Deferred Compensation Plan and the Orbital 401(k), (iii) any health
         or other benefit plans maintained by Orbital or its affiliates, (iv)
         other matters referred to herein, and (v) Orbital's interaction with
         you up to the date of execution of this Agreement, including, but not
         limited to, any rights, actions, suits, claims, causes of action, or
         liability under (a) any federal, state or local statute or
         regulation, or (b) under common law principles, except claims or
         proceedings necessary to enforce the provisions of this Agreement,
         provided that you shall not be precluded from any action, suit or
         proceeding arising out of, pertaining to or based on facts not known
         to you as of the date of this Agreement. You further covenant and
         agree never to join in or commence any action, suit or proceeding, in
         law or in equity, or before any administrative agency, or to incite,
         encourage, or participate in any such action, suit or proceeding,
         against the Orbital Entities in any way pertaining to or arising out
         of your employment with Orbital, except claims or proceedings
         necessary to enforce the provisions of this Agreement. Orbital
         covenants and agrees not to commence any action, suit or proceeding,
         in law or in equity, against you, pertaining to or arising out of
         your employment with Orbital, except claims or proceedings necessary
         to enforce the provisions of this Agreement, provided that Orbital
         shall not be precluded from any action, suit or proceeding arising
         out of, pertaining to or based on facts not known to senior
         management of Orbital as of the date of this Agreement. This
         provision shall not release either party from its obligations under
         the Officer Indemnification Agreement between you and Orbital dated
         as of October 21, 1998.

         In connection with the settlement of the class action lawsuits
         relating to Orbital's restatement of its financial statements, you
         agree to review, execute and deliver any documents or agreements
         necessary to approve or implement such settlement including, but not
         limited to, the settlement agreement, the stipulation of settlement
         and a release of National Union Fire Insurance Company. In the event
         that the proposed settlement is changed in a manner that has a
         material adverse effect on you, you may reasonably decline to execute
         the related settlement documents and continue the litigation
         independently.

                                      4

<PAGE>   5

Jeffrey V. Pirone
August 2, 2000
Page Five

11.      Officer Indemnification and Employment Agreements

         The terms and conditions of the Officer Indemnification Agreement by
         and between you and Orbital dated as of October 21, 1998, the Officer
         Indemnification Agreement by and between you and Magellan Corporation
         ("Magellan") dated as of January 1, 1998, the Director
         Indemnification Agreement by and between you and Magellan as of
         January 1, 1998, the Director Indemnification Agreement by and
         between you and ORBCOMM Corporation as of May 1998 and the
         Indemnification Agreement by and between you and ORBCOMM Global as of
         May 1998, shall remain in full force and effect. Arnold & Porter
         shall continue to represent you as set forth in those certain
         agreements between you and Arnold & Porter dated March 19, 1999 and
         an addendum dated March 23, 1999, provided that Orbital shall have
         the right to select different counsel of equivalent experience and
         capability if it determines that it is in the best interests of the
         Company or required as a result of any conflict of interest. You
         shall be provided coverage under Orbital's Director & Officer
         insurance policy, if applicable, to the extent permissible by law,
         with respect to any damages relating to or arising in connection with
         your service as an officer of Orbital. The Executive Employment
         Agreement between you and Orbital dated October 15, 1998 and the
         Performance Share Agreement between you and Orbital dated July 21,
         1999 are hereby terminated effective July 21, 2000.

12.      Confidentiality

         You acknowledge that you have held a sensitive management position
         with Orbital and that, by virtue of having held such position, you
         have had access to and have learned confidential and proprietary
         information. You agree that until, and for a period of three years
         after the Employment Termination Date, you shall hold in confidence
         and not directly or indirectly disclose any confidential or
         proprietary information of Orbital or any of Orbital's subsidiaries
         or affiliates to any person or entity, or use any such confidential
         and proprietary information for any purpose, except as authorized by
         Orbital, provided that the foregoing restrictions shall not apply to
         information that becomes known to and available for use by the public
         other than as a result of your unauthorized acts or failures to act.
         You acknowledge that all materials that in any way contain,
         incorporate or reflect confidential or proprietary information of
         Orbital or any of Orbital's subsidiaries or affiliates, including but
         not limited to documents, reports, plans, notes, memoranda, sketches,
         drawings, discs and records (including electronic records), shall
         belong exclusively to Orbital. You agree to promptly deliver to
         Orbital all copies of such materials that you may possess or have
         under your control upon your Employment Termination Date or at the
         request of the Chief Executive Officer or General Counsel. You also
         agree not to disclose to any other person or entity the terms of this
         Agreement and agree not to disparage Orbital, its officers,
         affiliates or employees in any way and not

                                      5

<PAGE>   6

Jeffrey V. Pirone
August 2, 2000
Page Six

         to engage in any conduct or make statements contrary to the interests
         of Orbital, its affiliates, officers or employees, except as may be
         required by law.

13.      Orbital Property

         On the Employment Termination Date or at the request of the Chief
         Executive Officer or General Counsel, you agree to return to Orbital
         all Orbital property in your possession, including computer
         equipment, fax machines, telephones, keys, credit cards, files and
         records.

14.      Noncompetition

         For two years from the date of this Agreement, except with the
         express written consent of the Chief Executive Officer, which consent
         shall not be unreasonably withheld, you agree not to perform
         consulting services for, or receive full-time or part-time employment
         from, any person or entity involved in a business that competes with
         any existing or planned business of Orbital or its subsidiaries or
         affiliates.

15.      Binding Agreement

         This Agreement shall be binding upon and shall inure to the benefit
         of the parties hereto and their respective heirs, devisees,
         executors, administrators, legal representatives, successors and
         assigns.

16.      Notice

         For the purposes of the Agreement, notices and all other
         communications provided for in this Agreement shall be in writing and
         shall be deemed to have been duly given when delivered or mailed by
         registered mail, return receipt requested, postage prepaid, addressed
         (i) if to Orbital, to Orbital Sciences Corporation, 21700 Atlantic
         Boulevard, Dulles, Virginia 20166, Attn: Legal Department, and (ii)
         if to you, to the address set forth on the first page of this
         Agreement, or to such other address as either party may have
         furnished to the other in writing in accordance herewith, except that
         notice of change of address shall be effective only upon receipt.

17.      Miscellaneous

         You and Orbital agree that no provision of this Agreement may be
         modified, waived or discharged and no amendment or addition to this
         Agreement shall be binding unless such waiver, modification,
         discharge, amendment or addition is agreed to in writing, signed by
         both you and Orbital, and to the extent necessary, approved or
         authorized Orbital's Board of Directors or a committee thereof. No
         waiver by you or Orbital of any breach by the

                                      6

<PAGE>   7

Jeffrey V. Pirone
August 2, 2000
Page Seven

         other, or compliance with, any condition or provision of this
         Agreement to be performed by the other party shall be deemed a waiver
         of similar or dissimilar provision of conditions at the same or at
         any prior or subsequent time. You and Orbital agree that no
         agreements or representations, oral or otherwise, express or implied,
         with respect to the subject matter hereof have been made by either
         party which are not expressly set forth in this Agreement, and this
         Agreement supersedes all prior agreements between Orbital and you
         with respect to the subject matter herein. The validity,
         interpretation, construction and performance of the Agreement shall
         be governed by the local laws of the Commonwealth of Virginia
         (regardless of the laws that might otherwise govern under principles
         of conflicts of law).

18.      Validity

         The invalidity or unenforceability of any provision of this Agreement
         shall not affect the validity or enforceability of any other
         provision of this Agreement, which shall remain in full force and
         effect.

19.      Remedy for Breach

         In the event of a material breach of this Agreement, you and Orbital
         agree and consent that the non-breaching party shall be entitled to a
         decree of specific performance and injunctive or other equitable
         relief in addition to all other remedies available at law.

20.      Executed Counterparts

         This Agreement may be executed in counterpart and by facsimile.

It has been a great pleasure working with you during the past nine years and I
deeply appreciate all that you have done for Orbital in that time. I look
forward to continuing to work with you on the terms set out above.

Sincerely,

/s/ David W. Thompson

David W. Thompson
Chief Executive Officer

Acknowledged and Agreed:

/s/ Jeffrey V. Pirone
----------------------------------
Jeffrey V. Pirone
Dated:  August 3, 2000

                                      7<PAGE>   1
                        EXECUTIVE EMPLOYMENT AGREEMENT

August 9, 2000

Mr. Garrett E. Pierce
Orbital Sciences Corporation
21700 Atlantic Blvd.
Dulles, Virginia  20166

Dear Garrett:

         This letter agreement (the "Agreement") sets forth the severance
benefits that Orbital Sciences Corporation and its subsidiaries (together, the
"Company") agrees will be provided to you in the event your employment with
the Company terminates under the circumstances described below. This Agreement
is not an employment contract nor does it alter your status as an at-will
employee of the Company.

         1.       Term.  This Agreement commences as of August 9, 2000, and
shall remain in effect so long as you are employed as an executive officer of
the Company.

         2.       Relationship to Executive Employment Change of Control
Agreement. This Agreement shall govern the severance benefits you shall
receive from the Company in the event your employment is terminated, except in
the event your employment is terminated in anticipation of or within two years
following a "Change in Control" as that term is defined in your Executive
Employment Change of Control Agreement, in which case your Executive
Employment Change of Control Agreement shall govern.

         3.       Termination.  You shall be entitled to the benefits provided
in Section 4 of this Agreement if your employment is terminated by the Company
for Disability or Cause, as described below, or by the Company for any reasons
other than Cause or Disability, or by you for Good Reason, as described below.

                  (i)      Disability. If, as a result of your incapacity due
to physical or mental illness, you shall have been absent from your duties
with the Company on a full-time basis for nine consecutive months, and within
30 days after written notice of termination is given you shall not have
returned to the full-time performance of your duties, the Company may
terminate your employment for "Disability."

<PAGE>   2

Mr. Garrett E. Pierce
Orbital Sciences Corporation
August 9, 2000
Page 2

                  (ii)     Cause. Termination by the Company of your
employment for "Cause" shall mean termination on (A) the willful gross neglect
of your duties with the Company as such duties are determined by the Board or
the executive officers to whom you report (other than any such failure
resulting from your incapacity due to physical or mental illness), after a
demand for substantial performance is delivered to you by the Board which
specifically identifies the manner in which the Board believes that you have
substantially neglected your duties, or (B) the willful engaging by you in
gross misconduct which is demonstrably and materially injurious to the
Company, monetarily or otherwise. For purposes of this Subsection, no act, or
failure to act, on your part shall be considered "willful" unless done, or
omitted to be done, by you not in good faith and without reasonable belief
that your action or omission was in the best interest of the Company.
Notwithstanding the foregoing, you shall not be deemed to have been terminated
for Cause unless and until there shall have been delivered to you a copy of a
resolution duly adopted by the affirmative vote of not less than two-thirds of
the entire membership of the Board at a meeting of the Board called and held
for the purpose (after reasonable notice to you and an opportunity for you,
together with your counsel, to be heard before the Board), finding that in the
good faith opinion of the Board you were guilty of conduct set forth above in
clause (A) or (B) of the first sentence of this Subsection and specifying the
particulars thereof in detail.

                  (iii)    Good Reason.  You shall be entitled to terminate
your employment for Good Reason.  For purposes of this Agreement, "Good
Reason" shall mean:

                  (A)      without your written consent, the assignment to you
         of any position (including status, offices, titles and reporting
         requirements), authorities, duties and responsibilities, that are not
         at least commensurate in all material respects with the most
         significant of those held, exercised and assigned by you at any time
         during the previous 180-day period, or any other action by the
         Company that results in a diminution in such position, authority,
         duties or responsibilities, excluding for this purpose an isolated,
         insubstantial and inadvertent action not taken in bad faith and that
         is remedied by the Company promptly after receipt of notice thereof
         given by you;

                  (B)      a failure to nominate, or renominate you to a
         position on the Board of Directors of the Company;

                  (C)      a reduction by the Company in your annual base
         salary ("Annual Base Salary"), which for the purposes of this
         Agreement shall mean an amount at least equal to 12 times the highest
         monthly base salary paid or payable, including any base salary that
         has been earned but deferred, to you by the Company in respect of the
         previous 12-month period;

                  (D)      the Company's requiring you to be based anywhere
         other than the office of the Company in which you are based in the
         previous 180-day period or any office or location within a 50 mile
         radius of such office, except for required travel on the

<PAGE>   3

Mr. Garrett E. Pierce
Orbital Sciences Corporation
August 9, 2000
Page 3

         Company's business to an extent substantially consistent with your
         business travel obligations within the previous 180-day period;

                  (E)      the failure by the Company to continue in effect
         any compensation plan in which you participate, or to provide you
         with plans substantially similar, including but not limited to any
         stock purchase plan, stock option plan, incentive compensation,
         bonus, and other plan in which you were participating in the previous
         180-day period, or the failure by the Company to continue your
         participation therein;

                  (F)      the failure by the Company to continue to provide
         you with benefits substantially similar to those enjoyed by you under
         any of the Company's retirement, pension, 401(k), deferred
         compensation, life insurance, medical, health, accident, disability
         or other benefit plans in which you were participating in the
         previous 180-day period, the taking of any action by the Company
         which would directly or indirectly materially reduce any of such
         benefits enjoyed by you in the previous 180-day period, or the
         failure by the Company to provide you with the number of paid
         vacation days to which you are entitled in accordance with the
         Company's normal vacation policy in effect in the previous 180-day
         period;

                  (G)      the failure of the Company to obtain a satisfactory
         agreement from any successor to assume and agree to perform this
         Agreement, as contemplated in Section 5 hereof; or

                  (H)      any termination of your employment which is not
         effected pursuant to a Notice of Termination satisfying the
         requirements of Section 3(iv) hereof (and, if applicable, Section
         3(ii) hereof); and for purposes of this Agreement, no such purported
         termination shall be effective.

                   (iv)    Notice of Termination. Any termination by the
Company or by you shall be communicated by written Notice of Termination to
the other party hereto in accordance with Section 6 hereof, and if by the
Company for Cause, shall not be effective unless such notice includes the
information set forth in Section 3(ii) hereof.

                  (v)      Date of Termination, etc. "Date of Termination"
shall mean (A) if your employment is terminated by reason of death or
Disability, the date of your death or 30 days after Notice of Termination is
given (provided that you shall not have returned to the performance of your
duties on a full-time basis during such 30 day period), as the case may be,
(B) if your employment is terminated by the Company for Cause or for any other
reason, the date specified in the Notice of Termination which shall not be
less than 30 days from the date such Notice of Termination is given, and (C)
if you terminate your employment for "Good Reason," the date such Notice of
Termination is given or any later date specified therein.

<PAGE>   4

Mr. Garrett E. Pierce
Orbital Sciences Corporation
August 9, 2000
Page 4

         4.        Benefits Upon Termination or During Disability.

                  (i)      During any period that you fail to perform your
duties hereunder as a result of incapacity due to physical or mental illness,
and in the event your employment is terminated pursuant to Section 3(i)
hereof, your benefits shall be determined in accordance with the Company's
insurance and benefit programs then in effect. Your stock options shall
continue to vest as scheduled for a 24-month period following your termination
and remain exercisable for the rest of the originally scheduled term.

                  (ii)     If your employment shall be terminated for Cause or
by you without Good Reason, the Company shall pay you your full base salary
through the Date of Termination at the rate in effect at the time Notice of
Termination is given, as well as any accrued, but unpaid amounts. You shall
have 60 days to exercise your vested options and your unvested options shall
be forfeited. The Company shall have no further obligations to you under this
Agreement.

                  (iii)    If your employment shall be terminated (a) by the
Company for any reason other than for Cause or Disability or (b) by you for
Good Reason, then you shall be entitled to all the benefits provided below:

                  (A)      The Company shall pay you on the Date of
         Termination your full base salary through the Date of Termination at
         the rate in effect at the time Notice of Termination is given.

                  (B)      In lieu of any further salary payments to you for
         periods subsequent to the Date of Termination, the Company shall pay
         to you, not later than 15 days following the Date of Termination, a
         lump sum payment equal to two times the sum of (i) your Annual Base
         Salary and (ii) the higher of (x) the sum of any incentive, annual
         and other cash bonuses, paid or payable to you for the 12-month
         period immediately preceding the month of your termination or (y) the
         target bonus for the year of termination, based on 60% of your Annual
         Base Salary (provided that for the first year of your employment,
         such amount shall be construed to be your minimum guaranteed bonus of
         $200,000).

                   (C)     The Company shall also pay to you all reasonable
         legal fees and expenses incurred by you as a result of such
         termination (including all such fees and expenses, if any, incurred
         in contesting or disputing any such termination or in seeking to
         obtain or enforce any right or benefit provided by this Agreement)
         upon presentation to the Company of a reasonably detailed invoice for
         such expenses, whether or not you have already made payment for such
         expenses.

                  (D)      For a 24-month period after such termination, the
         Company shall arrange to provide you with life, disability, accident
         and health insurance benefits substantially similar to those you were
         receiving immediately prior to the Notice of Termination,

<PAGE>   5

Mr. Garrett E. Pierce
Orbital Sciences Corporation
August 9, 2000
Page 5

         provided, however, that should the Company be unable to provide for
         any such benefits under the terms of the benefit plans, or by law,
         the Company shall pay you an amount equal to the premiums the Company
         would have paid for such benefits under such plans, grossed-up for
         taxes.

                  (E)      Your stock options shall continue to vest as
         scheduled for a 24-month period following your termination and all
         vested stock options shall remain exercisable for the rest of their
         originally scheduled terms.

                  (F)      You shall not be required to mitigate the amount of
         any payment provided for in this Section 4 by seeking other
         employment or otherwise, nor shall the amount of any payment or
         benefit provided for in this Section 4 be reduced by any compensation
         earned by you as the result of employment by another employer or by
         retirement benefits after the Date of Termination, or otherwise.

                  (G)      In addition to all other amounts payable to you
         under this Section 4, you shall be entitled to receive all benefits
         payable to you under any of the Company's plans or agreements
         relating to retirement benefits.

                  (iv)     All payments required to be made by the Company
hereunder to you shall be subject to the withholding of such amounts relating
to Federal, state, local or foreign taxes as the Company reasonably may
determine it should withhold pursuant to any applicable law or regulation.

         5.       Successors; Binding Agreement.

                  (i)      The Company will require any successor (whether
direct or indirect, by purchase, merger, consolidation or otherwise) to all or
substantially all its business and/or assets to expressly assume and agree to
perform this Agreement in the same manner and to the same extent that the
Company would be required to perform it if no such succession had taken place.
Failure of the Company to obtain such assumption and agreement no later than
ten days prior to the effectiveness of any such succession shall be a breach
of this Agreement and shall entitle you to compensation from the Company in
the same amount and on the same terms as you would be entitled under section
4(iii), except that for purposes of implementing the foregoing, a date ten
days prior to the date on which any such succession becomes effective shall be
deemed the Date of Termination. As used in this Agreement, "the Company" shall
mean the Company, as hereinbefore defined and any successor to its business
and/or assets that assumes and agrees to perform this Agreement by executing
and delivering the agreement provided for in this paragraph 5, by operation of
law, or otherwise.

                  (ii)     This Agreement shall inure to the benefit of and be
enforceable by your personal or legal representatives, executors,
administrators, successors, heirs, distributees,

<PAGE>   6

Mr. Garrett E. Pierce
Orbital Sciences Corporation
August 9, 2000
Page 6

devisees, and legatees. If you should die while any amount would still be
payable to you hereunder, all such amounts, unless otherwise provided herein,
shall be paid in accordance with the terms of this Agreement to your devisee,
legatee or other designee or if there is no such designee, to your estate.

         6.       Notice. For the purposes of this Agreement, notices and all
other communications provided for in this Agreement shall be in writing and
shall be deemed to have been duly given when delivered or mailed by registered
mail, return receipt requested, postage prepaid, addressed (i) if to the
Company, to Orbital Sciences Corporation, 21700 Atlantic Boulevard, Dulles,
Virginia 20166, Attn: Secretary of the Company, and (ii) if to you, to the
address set forth on the first page of this Agreement, or to such other
address as either party may have furnished to the other in writing in
accordance herewith, except that notice of change of address shall be
effective only upon receipt.

         7.       Miscellaneous. No provision of this Agreement may be
modified, waived or discharged unless such waiver, modification or discharge
is agreed to in writing and signed by you and such officer as may be
specifically designated by the Board. No waiver by either party hereto at any
time of any breach by the other party hereto of, or compliance with, any
condition or provision of this Agreement to be performed by such other party
shall be deemed a waiver of similar or dissimilar provisions or conditions at
the same or at any prior or subsequent time. No agreements or representations,
oral or otherwise, express or implied, with respect to the subject matter
hereof have been made by either party which are not expressly set forth in
this Agreement, and this Agreement supersedes all prior agreements between the
Company and you with respect to the subject matter herein. The validity,
interpretation construction and performance of this Agreement shall be
governed by the local laws of the Commonwealth of Virginia (regardless of the
laws that might otherwise govern under principles of conflicts of law).

         8.       Validity.  The invalidity or unenforceability of any
provision of this Agreement shall not affect the validity or enforceability of
any other provision of this Agreement, which shall remain in full force and
effect.

         9.       Counterparts.  This Agreement may be executed in several
counterparts, each of which shall be deemed to be an original but all of which
together will constitute one and the same instrument.

         10.      Arbitration. Any dispute or controversy arising under or in
connection with this Agreement shall be settled exclusively by arbitration in
Washington, D.C. in accordance with the domestic rules of the American
Arbitration Association then in effect. Pending the resolution of such dispute
or controversy, the Company will continue to pay you your full base salary in
effect when the notice giving rise to the dispute was given and you will
continue as a participant in all incentive compensation, stock option,
retirement, deferred compensation, pension, life, disability, health and
accident plans in which you were participating when the notice giving rise to
dispute

<PAGE>   7

Mr. Garrett E. Pierce
Orbital Sciences Corporation
August 9, 2000
Page 7

was given, unless you have already received all benefits payable under Section
4(iii) of this Agreement. Judgment may be entered on the arbitrator's award in
any court having jurisdiction; provided, however, that you shall be entitled to
seek specific performance of your right to be paid until the Date of Termination
during the pendency of any dispute or controversy arising under or in connection
with this Agreement.

         If this Agreement correctly sets forth our agreement on the subject
matter hereof, kindly sign both of the enclosed copies, keeping one for your
files and returning the other to the Company.

Sincerely,

ORBITAL SCIENCES CORPORATION

/s/ David W. Thompson
-------------------------------------------
By:  David W. Thompson
     Chairman and Chief Executive Officer

Agreed to:

/s/ Garrett E. Pierce
-------------------------------------------
Name:  Garrett E. Pierce
Date:  August 9, 2000

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