Document:

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                                                                   EXHIBIT 10.16

January 29, 2001

Mr. Robert D. Strain
17919 Hickman Street
Poolesville, Maryland  20837

Dear Rob:

        This letter (the "Letter") amends the Agreement dated July 7, 2000
between you and the Company and sets forth the terms and conditions under which
Orbital may make certain payments to you. Capitalized terms that are used in
this Letter shall have the same meaning as in the Agreement unless defined in
this Letter.

1.      Amendments to Agreement.

        a. Section one of the Agreement is amended in entirety to read as
follows:

                "Term. This Agreement shall commence July 7, 2000 and shall
                terminate on January 9, 2002."

        b. Section three of the Agreement is amended by:

                (i) amending in its entirety the first sentence of the Section
                to delete the words "or within twelve (12) months after the
                closing of the Transaction."

                (ii) amending in its entirety Section 3(iii)(A) to read as
                follows:

                        "(A) without your written consent, the assignment to you
                of any position, authorities, duties and responsibilities each
                of which is not at least commensurate in all material respects,
                including, but not limited to, area of expertise, with the most
                significant of those held and exercised by and assigned to you
                as of January 1, 2001, 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;"

        c.  Section four of the Agreement is amended by:

                (i) amending clause (iii) to delete the words "or within twelve
                (12) months after the closing of a Transaction;" and

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Mr. Robert D. Strain
January 29, 2001
Page 2

                (ii) amending in its entirety iii(B) to read as follows:

                        "(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 fifteen (15) days following Date of
                Termination, a lump sum payment equal to $344,250."

        2. Additional Payments.

        a. In consideration of your agreement to the amendments in this Letter,
the Company agrees to pay to you in connection with the Transaction an
additional amount of $229,500. The Company shall pay such additional amount by
February 9, 2001.

        b. The Company is exploring various alternatives with respect to the
Sensors division in Pomona, California and the Transportation Management Systems
division in Columbia, Maryland (each, a "Division" and collectively, the
"Divisions"), including the sale of each of the Divisions to a third party. In
consideration of your continued support and assistance in connection with the
sale of the Divisions, Orbital agrees to pay you $344,250 on the earlier of (i)
the closing of the sale of either Division or (ii) December 31, 2001, provided
however that no payment shall be made and the obligation of the Company to make
any such payment shall cease in the event that you seek or receive payments
pursuant to Section 4(iii) of the Agreement. In the event a payment is made to
you under this Section, (i) you shall be entitled to receive, upon termination
of your employment with the Company, the benefits set forth in Section 4(iii)(C)
and (D) of the Agreement and (ii) all other provisions of the Agreement shall
terminate immediately and be of no further force and effect.

        c. All payments made by the Company to you under this Section 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.

        3.  Successors; Binding Letter.

        a. This Letter shall be binding upon and shall inure to the benefit of
you and the Company and the Company's successors and assigns.

        b. This Letter shall inure to the benefit of and be enforceable by your
personal or legal representatives, executors, administrators, successors, heirs,
distributees, 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 Letter to your
devisee, legatee or other designee or if there is no such designee, to your
estate.

        4. Miscellaneous. No provision of this Letter 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 of Directors of Orbital. No waiver by either party hereto at any time of
any breach by the other party hereto of, or compliance with,

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Mr. Robert D. Strain
January 29, 2001
Page 3

any condition or provision of this Letter 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 Letter.
The validity, interpretation, construction and performance of this Letter shall
be governed by the local laws of the State of Delaware (regardless of the laws
that might otherwise govern under principles of conflicts of law). Except as
modified or amended by this Letter, the terms, provisions and conditions of the
Agreement remain in full force and effect.

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

        6. Counterparts. This Letter 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.

        7. Arbitration. Any dispute or controversy arising under or in
connection with this Letter shall be settled exclusively by arbitration in
Washington, D.C. in accordance with the domestic rules of the American
Arbitration Association then in effect. Judgment may be entered on the
arbitrator's award in any court having jurisdiction.

        If this Letter 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.

Very truly yours,

ORBITAL SCIENCES CORPORATION

David W. Thompson
Chief Executive Officer

Agreed to:

-----------------------------------
Name:  Robert D. Strain
Date:<PAGE>   1

                                                                  EXECUTION COPY

                                                                   EXHIBIT 10.25

                      AMENDED AND RESTATED PLEDGE AGREEMENT

        AMENDED AND RESTATED PLEDGE AGREEMENT dated as of November 30, 1999 and
amended and restated as of February 23, 2001 among ORBITAL SCIENCES CORPORATION
(with its successors, the "BORROWER"), each of the Subsidiaries of the Borrower
listed on the signature pages hereof and each other Subsidiary of the Borrower
that may from time to time become a party to this Agreement (each such
Subsidiary, with its successors, a "SUBSIDIARY PLEDGOR" and together with the
Borrower, the "PLEDGORS") MORGAN GUARANTY TRUST COMPANY OF NEW YORK, as
Collateral Agent (with its successors, the "COLLATERAL AGENT" ).

                              W I T N E S S E T H:

        WHEREAS, the Borrower, certain banks listed therein, Morgan Guaranty
Trust Company of New York, as administrative agent (the "ADMINISTRATIVE AGENT")
and the Collateral Agent have entered into a 364-Day Senior Credit Agreement
dated as of February 23, 2001 (as amended from time to time, the "NEW
AGREEMENT"); and

        WHEREAS, the Borrower and certain of its Subsidiaries, certain banks
listed therein, the Collateral Agent and the Administrative Agent are parties to
a Third Amended and Restated Credit Agreement dated as of December 21, 1998 (as
heretofore amended, as amended and restated by Amendment No. 13 thereto dated as
of the date hereof ("AMENDMENT NO. 13") and as the same may be further amended
from time to time hereafter, the "EXISTING AGREEMENT"); and

        WHEREAS, the Pledgors and the Collateral Agent have entered into a
Pledge Agreement dated as November 30, 1999 (the "EXISTING PLEDGE AGREEMENT");
and

        WHEREAS, pursuant to the New Agreement and Amendment No. 13, the
Borrower and Subsidiary Pledgors party hereto are required to enter into a
pledge agreement substantially in the form hereof; and

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        NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Existing Pledge Agreement is amended and restated in its
entirety as follows:

        SECTION 1. Definitions . Terms defined in the Credit Agreements and not
otherwise defined herein have, as used herein, the respective meanings provided
for therein. The following additional terms, as used herein, have the following
respective meanings:

        "COLLATERAL" has the meaning assigned to such term in Section 3(a).

        "CREDIT AGREEMENT" means the New Agreement or the Existing Agreement,
and "CREDIT Agreements" means the New Agreement and the Existing Agreement.

        "DEFAULT" means a Default as defined in either Credit Agreement.

        "DOMESTIC ISSUER" means any Issuer that is incorporated in the United
States or any State thereof.

        "EVENT OF DEFAULT" means an Event of Default as defined in either Credit
Agreement.

        "EXISTING ISSUER" means each Person listed on Schedule I under the
heading "Existing Issuer".

        "FINANCING DOCUMENT" means any Financing Document as defined in either
Credit Agreement.

        "ISSUER" means (i) each Existing Issuer and (ii) each New Issuer.

        "JUNIOR BANK PARTIES" means the Administrative Agent under the Existing
Agreement, each Bank from time to time party to the Existing Agreement and the
Treasury Management Bank.

        "JUNIOR BANK SECURED OBLIGATIONS" means:

        (x)     with respect to the Borrower, (a) all principal of and interest
(including, without limitation, any interest which accrues after the
commencement of any case, proceeding or other action relating to the bankruptcy,
insolvency or reorganization of the Borrower, whether or not allowed or
allowable as a claim in any such proceeding) on any loan to the Borrower under,
or any note issued by the Borrower pursuant to, the Existing Agreement, (b) all
Reimbursement Obligations and all interest thereon (including, without
limitation, any interest which accrues after the commencement of any case,
proceeding or other action relating to the

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bankruptcy, insolvency or reorganization of the Borrower, whether or not allowed
or allowable as a claim in any such proceeding), (c) all other amounts payable
by the Borrower under any Financing Document in respect of or relating to the
Existing Agreement, and (d) any renewals or extensions of any of the foregoing;
and

        (y)     with respect to the Borrower, all amounts payable by the
Borrower pursuant to the Treasury Management Agreement; provided that such
amounts shall not constitute Junior Bank Secured Obligations to the extent the
aggregate amount thereof exceeds $4,300,000; and

        (z)     with respect to each Subsidiary Pledgor, all obligations of such
Subsidiary Pledgor incurred by such Subsidiary Pledgor pursuant to Section 23 of
the Security Agreement with respect to the obligations described in (x) and (y)
above.

        "JUNIOR SECURED OBLIGATIONS" means the Junior Bank Secured Obligations
and the NML Secured Obligations.

        "JUNIOR SECURED PARTIES" means the Junior Bank Parties and NML.

        "LETTER OF CREDIT OBLIGATION" means, at any time, any Reimbursement
Obligations or other obligation to make a payment in connection with a Letter of
Credit issued under the Existing Agreement, including contingent obligations
with respect to amounts which are then, or may thereafter become, available for
drawing under such Letter of Credit.

        "NEW ISSUER" has the meaning assigned to such term in clause (i) of
Section 3(b).

        "NML GUARANTY AGREEMENT" means the Guaranty dated as of November 30,
1999 among the Subsidiary Pledgors and NML.

        "NML NOTE AGREEMENT" means the agreement dated as of June 1, 1995 (as
amended from time to time) between the Borrower and The Northwestern Mutual Life
Insurance Company (with its successors and assigns, "NML").

        "NML SECURED OBLIGATIONS" means:

        (x)     with respect to the Borrower, (a) all principal of and interest
on any note issued by the Borrower pursuant to the NML Note Agreement
(including, without limitation, any interest which accrues after the
commencement of any case, proceeding or other action relating to the bankruptcy,
insolvency or reorganization of the Borrower, whether or not allowed or
allowable as a claim in any such proceeding), (b) all other amounts, including
without limitation, make-whole amount, if any, payable by the Borrower under the
NML Note Agreement and (c) any renewals or extensions of any of the foregoing;
and

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        (y)     with respect to each Subsidiary Pledgor, all obligations of such
Subsidiary Pledgor incurred by such Subsidiary Pledgor pursuant to the NML
Guaranty Agreement or pursuant to Section 23 of the Security Agreement with
respect to the obligations described in (x) above.

        "PLEDGED INSTRUMENTS" means any instrument required to be pledged to the
Collateral Agent pursuant to Section 3(b).

        "PLEDGED SECURITIES" means the Pledged Instruments and the Pledged
Stock.

        "PLEDGED STOCK" means, with respect to each Pledgor, (i) the capital
stock, limited liability company interests, partnership interests or other
equity interests of each Existing Issuer described on Schedule I (attached
hereto) opposite the name of such Existing Issuer held by such Pledgor and (ii)
any other capital stock, limited liability company interests, partnership
interests or other equity interests of any Issuer required to be pledged by such
Pledgor to the Collateral Agent pursuant to Section 3(b).

        "REQUIRED BANKS" means (i) until such time as all Loans outstanding
under the New Agreement have been paid in full, together with accrued interest
thereon and all other amounts then due under the New Agreement, and the
Commitments thereunder shall have terminated, the Required Banks as defined in
the New Agreement and (ii) thereafter, the Required Banks as defined in the
Existing Agreement.

        "SECURED OBLIGATIONS" means:

        (x)     with respect to the Borrower, (a) the Senior Secured Obligations
of the Borrower, (b) the Junior Bank Secured Obligations of the Borrower and (c)
the NML Secured Obligations of the Borrower; and

        (y)     with respect to each Subsidiary Pledgor, (a) the Senior Secured
Obligations of the Subsidiary Pledgor, (b) the Junior Bank Secured Obligations
of such Subsidiary Pledgor and (c) the NML Secured Obligations of such
Subsidiary Pledgor.

        "SECURED PARTIES" means the Senior Secured Parties, the Junior Secured
Parties and the Collateral Agent.

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        "SECURITY INTERESTS" means the security interests in the Collateral
granted hereunder securing the Secured Obligations.

        "SENIOR SECURED OBLIGATIONS" means:

        (x)     with respect to the Borrower, (a) all principal of and interest
(including, without limitation, any interest which accrues after the
commencement of any case, proceeding or other action relating to the bankruptcy,
insolvency or reorganization of the Borrower, whether or not allowed or
allowable as a claim in any such proceeding) on any loan to the Borrower under,
or any note issued by the Borrower pursuant to, the New Agreement, (b) all other
amounts payable by the Borrower under any Financing Document in respect of or
relating to the New Agreement and (c) any renewals or extensions of any of the
foregoing; and

        (y)     with respect to each Subsidiary Pledgor, all obligations of such
Subsidiary Pledgor incurred by such Subsidiary Pledgor pursuant to Section 23 of
the Security Agreement with respect to the obligations described in (x) above.

        "SENIOR SECURED PARTIES" means the Administrative Agent under the New
Agreement and each bank from time to time party to the New Agreement.

        "TREASURY MANAGEMENT AGREEMENT" means the treasury management
arrangement established by the Treasury Management Bank for the benefit of the
Company, as evidenced by, among other things, that certain zero Balance Account
Service Agreement dated as of May 15, 1997 and that certain Authorization and
Agreement for Treasury Services dated as of the date hereof, including those
accounts bearing account numbers 4113052459, 4122852365, 79176554 and
4113052381, and such other accounts as are or may be established in connection
therewith.

        "TREASURY MANAGEMENT BANK" means Bank of America, N.A., in its capacity
as provider of treasury management services under the Treasury Management
Agreement. The term shall also include any affiliate providing such services
under the Treasury Management Agreement.

        Unless otherwise defined herein, or unless the context otherwise
requires, all terms used herein which are defined in the New York Uniform
Commercial Code as in effect on the date hereof shall have the meanings therein
stated.

        SECTION 2. Representations and Warranties . Each Pledgor represents and
warrants as follows:

        (a)     Title to Pledged Securities. Such Pledgor owns all of the
Pledged Securities, free and clear of any Liens other than the Security
Interests. The Pledged Stock includes all of the issued and outstanding capital
stock or other equity interests of each Issuer held by such Pledgor. All of the
Pledged Stock

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constituting capital stock or other equity interests of any Person that is a
Subsidiary of such Pledgor has been duly authorized and validly issued, and is
fully paid and non-assessable, and is subject to no options to purchase or
similar rights of any Person. Such Pledgor is not and will not become party to
or otherwise bound by any agreement (other than this Agreement and the NML Note
Agreement, which restricts in any manner the rights of any present or future
holder of any of the Pledged Securities with respect thereto. The parties hereto
acknowledge that the NML Note Agreement contains restrictions on the ability of
the Borrower and its Subsidiaries to grant Liens on their respective assets.
Each Pledgor represents and warrants that the execution, delivery and
performance by such Pledgor of this Agreement (including without limitation the
granting by such Pledgor of the Security Interests on such Pledgor's Collateral)
does not contradict, or constitute a default under, the NML Note Agreement.

        (b)     Validity, Perfection and Priority of Security Interests. Upon
the delivery of the Pledged Instruments and certificates representing the
Pledged Stock to the Collateral Agent in accordance with Section 4 hereof, the
Collateral Agent will have valid and perfected security interests in the
Collateral (other than any Pledged Stock not evidenced by certificates) subject
to no prior Lien. Upon the filing of financing statements listing such Pledgor
as "debtor" and the Collateral Agent as "secured party" in the locations where
such filing must be made under the UCC in order to perfect a security interest
in collateral consisting of general intangibles, the Collateral Agent will have
valid and perfected security interests in the Collateral of such Pledgor
consisting of Pledged Stock not evidenced by certificates, subject to no prior
Lien. Except as set forth in the immediately preceding sentence, no
registration, recordation or filing with any governmental body, agency or
official is required in connection with the execution or delivery of this
Agreement or necessary for the validity or enforceability hereof or for the
perfection or enforcement of the Security Interests. None of the Pledgor or any
of their respective Subsidiaries has performed or will perform any acts which
might prevent the Collateral Agent from enforcing any of the terms and
conditions of this Agreement or which would limit the Collateral Agent in any
such enforcement.

        (c)     UCC Filing Locations. The chief executive office of each Pledgor
is located at the address set forth on Schedule II opposite the name of such
Pledgor (or on a counterpart of this Agreement executed by such Pledgor and
pursuant to which such Pledgor has become a party to this Agreement). Under the
Uniform Commercial Code as in effect in the State in which such office is
located, a local filing in the office set forth on Schedule II opposite such
Pledgor's name (or on such counterpart) is required to perfect a security
interest in collateral consisting of general intangibles.

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        SECTION 3. The Security Interests . (a) In order to secure the full and
punctual payment of the Junior Secured Obligations in accordance with the terms
thereof, and to secure the performance of all the obligations of each Pledgor
hereunder and under the other Financing Documents with respect thereto, each
Pledgor hereby assigns and pledges to and with the Collateral Agent for the
benefit of the Junior Secured Parties and grants to the Collateral Agent for the
benefit of the Junior Secured Parties security interests in the Pledged
Securities held by such Pledgor, and all of its rights and privileges with
respect to such Pledged Securities, and all income and profits thereon, and all
interest, dividends and other payments and distributions with respect thereto,
and all proceeds of the foregoing (the "COLLATERAL").

        The Security Interests granted pursuant to this Section 3(a) shall be
subordinate to the Security Interests granted pursuant to Section 3(b).

        (b)     In order to secure the full and punctual payment of the Senior
Secured Obligations in accordance with the terms thereof, and to secure the
performance of all the obligations of each Pledgor hereunder and under the other
Financing Documents with respect thereto, each Pledgor hereby assigns and
pledges to and with the Collateral Agent for the benefit of the Senior Secured
Parties and grants to the Collateral Agent for the benefit of the Senior Secured
Parties a continuing security interests in and to all Collateral of such
Pledgor.

        (c)     Prior to the execution and delivery hereof, each Pledgor has
delivered certificates representing the Pledged Securities held by such Pledgor
in pledge hereunder (other than any Pledged Stock not evidenced by
certificates).

                In the event that (i) any Pledgor at any time after the date
hereof creates or acquires any new direct Subsidiary or acquires the capital
stock, limited liability company interests, partnership interests or other
equity interests of any other Person (any such Subsidiary or other Person, a
"NEW ISSUER") or (ii) any Issuer at any time issues any additional or substitute
shares of capital stock, limited liability company interests, partnership
interests or other equity interests of any class or (iii) any Subsidiary of the
Borrower (including any New Issuer) owes any Debt to any Pledgor, such Pledgor
will within ten days thereafter pledge and deposit with the Collateral Agent
certificates (if any) representing all such shares, limited liability company
interests, partnership interests or other equity interests or an instrument (if
any) evidencing such other Debt as additional security for the Secured
Obligations; provided that (1) such Pledgor will not be required to take the
actions described in this subsection (c) with respect to the capital stock,
limited liability company interests, partnership interests or other equity
interests of any New Issuer that is not a Domestic Issuer to the extent the
aggregate capital stock, limited liability company interests, partnership
interests or other equity interests of such New Issuer subject to a Lien granted
to the Collateral Agent for the benefit of the Banks and NML would exceed 66% of
the outstanding capital stock, limited liability company interests, partnership
interests or other equity interests of such New Issuer and (2) such Pledgor will
not be required to take any of the actions described in this subsection (c) with
respect to the capital stock, limited

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liability company interests, partnership interests or other equity interests of
any New Issuer to the extent any such action is prohibited by the terms of any
agreement or instrument to which (aa) such New Issuer is a party or is bound as
in effect on the date such New Issuer becomes a direct Subsidiary of such
Pledgor, so long as such agreement or instrument was not entered into in
contemplation of such New Issuer becoming a Subsidiary of such Pledgor or (bb)
such Pledgor or any of its wholly-owned Subsidiaries incorporated in the United
States or any State thereof (other than such New Issuers) is a party or is bound
as in effect on October 15, 1999. All such shares and other equity interests,
notes and instruments constitute Pledged Securities and are subject to all
provisions of this Agreement.

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        (d)     The Security Interests are granted as security only and shall
not subject the Collateral Agent, any Bank or NML to, or transfer or in any way
affect or modify, any obligation or liability of each Pledgor or any of its
Subsidiaries with respect to any of the Collateral or any transaction in
connection therewith.

        SECTION 4. Delivery of Pledged Securities . All Pledged Instruments held
by each Pledgor shall be delivered to the Collateral Agent by such Pledgor
pursuant hereto indorsed to the order of the Collateral Agent, and accompanied
by any required transfer tax stamps, all in form and substance satisfactory to
the Collateral Agent. All certificates representing Pledged Stock delivered to
the Collateral Agent by each Pledgor pursuant hereto shall be in suitable form
for transfer by delivery, or shall be accompanied by duly executed instruments
of transfer or assignment in blank, with signatures appropriately guaranteed,
and accompanied by any required transfer tax stamps, all in form and substance
satisfactory to the Collateral Agent.

        SECTION 5. Further Assurances . (a) Each Pledgor agrees that it will, at
its expense and in such manner and form as the Collateral Agent may require,
execute, deliver, file and record any financing statement, specific assignment
or other paper and take any other action that may be necessary or desirable, or
that the Collateral Agent may request, in order to create, preserve, perfect or
validate any Security Interest or to enable the Collateral Agent to exercise and
enforce its rights hereunder with respect to any of the Collateral. To the
extent permitted by applicable law, each Pledgor hereby authorizes the
Collateral Agent to execute and file, in the name of such Pledgor or otherwise,
Uniform Commercial Code financing statements (which may be carbon, photographic,
photostatic or other reproductions of this Agreement or of a financing statement
relating to this Agreement) which the Collateral Agent in its sole discretion
may deem necessary or appropriate to further perfect the Security Interests.

        (b)     Each Pledgor agrees that it will not change (i) its name,
identity or corporate structure in any manner or (ii) the location of its chief
executive office unless it shall have given the Collateral Agent not less than
30 days' prior notice thereof.

        SECTION 6. Record Ownership of Pledged Stock . The Collateral Agent may
at any time or from time to time following the occurrence and during the
continuance of an Event of Default, in its sole discretion, cause any or all of
the Pledged Stock to be transferred of record into the name of the Collateral
Agent or its nominee. Each Pledgor will promptly give to the Collateral Agent
copies of any notices or other communications received by it with respect to
Pledged Stock registered in the name of such Pledgor and the Collateral Agent
will promptly give to such Pledgor copies of any notices and communications
received by the Collateral Agent with respect to Pledged Stock registered in the
name of the Collateral Agent or its nominee.

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        SECTION 7. Right to Receive Distributions on Collateral . The Collateral
Agent shall have the right to receive and, during the continuance of any
Default, to retain as Collateral hereunder all dividends, interest and other
payments and distributions made upon or with respect to the Collateral and each
Pledgor shall take all such action as the Collateral Agent may deem necessary or
appropriate to give effect to such right. All such dividends, interest and other
payments and distributions which are received by such Pledgor shall be received
in trust for the benefit of the Collateral Agent, the Secured Parties and, if
the Collateral Agent so directs during the continuance of a Default, shall be
segregated from other funds of such Pledgor and shall, forthwith upon demand by
the Collateral Agent during the continuance of a Default, be paid over to the
Collateral Agent as Collateral in the same form as received (with any necessary
endorsement). After all Defaults have been cured, the Collateral Agent's right
to retain dividends, interest and other payments and distributions under this
Section 7 shall cease and the Collateral Agent shall pay over to such Pledgor
any such Collateral retained by it during the continuance of a Default.

        SECTION 8. Right to Vote Pledged Stock . Unless a Default shall have
occurred and be continuing, each Pledgor shall have the right, from time to
time, to vote and to give consents, ratifications and waivers with respect to
the Pledged Stock.

        If a Default shall have occurred and be continuing, the Collateral Agent
shall have the right to the extent permitted by law and such Pledgor shall take
all such action as may be necessary or appropriate to give effect to such right,
to vote and to give consents, ratifications and waivers, and take any other
action with respect to any or all of the Pledged Stock with the same force and
effect as if the Collateral Agent were the absolute and sole owner thereof.

        SECTION 9. General Authority . Each Pledgor hereby irrevocably appoints
the Collateral Agent its true and lawful attorney, with full power of
substitution, in the name of such Pledgor, the Collateral Agent, the Secured
Parties or otherwise, for the sole use and benefit of the Collateral Agent, the
Secured Parties, but at the expense of such Pledgor, to the extent permitted by
law to exercise, at any time and from time to time while an Event of Default has
occurred and is continuing, all or any of the following powers with respect to
all or any of the Collateral:

        (a)     to demand, sue for, collect, receive and give acquittance for
any and all monies due or to become due upon or by virtue thereof,

        (b)     to settle, compromise, compound, prosecute or defend any action
or proceeding with respect thereto,

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        (c)     to sell, transfer, assign or otherwise deal in or with the same
or the proceeds or avails thereof, as fully and effectually as if the Collateral
Agent were the absolute owner thereof, and

        (d)     to extend the time of payment of any or all thereof and to make
any allowance and other adjustments with reference thereto;

provided that the Collateral Agent shall give such Pledgor not less than ten
days' prior notice of the time and place of any sale or other intended
disposition of any of the Collateral except any Collateral which is perishable
or threatens to decline speedily in value or is of a type customarily sold on a
recognized market. The Collateral Agent and the Pledgors agree that such notice
constitutes "reasonable notification" within the meaning of Section 9-504(3) of
the Uniform Commercial Code.

        SECTION 10. Remedies upon Event of Default . If any Event of Default
shall have occurred and be continuing, the Collateral Agent may exercise on
behalf of the Secured Parties all the rights of a secured party under the
Uniform Commercial Code (whether or not in effect in the jurisdiction where such
rights are exercised) and, in addition, the Collateral Agent may, without being
required to give any notice, except as herein provided or as may be required by
mandatory provisions of law, (i) apply the cash, if any, then held by it as
Collateral as specified in Section 13 and (ii) if there shall be no such cash or
if such cash shall be insufficient to pay all the Secured Obligations in full,
sell the Collateral or any part thereof at public or private sale or at any
broker's board or on any securities exchange, for cash, upon credit or for
future delivery, and at such price or prices as the Collateral Agent may deem
satisfactory. Any Bank or NML may be the purchaser of any or all of the
Collateral so sold at any public sale (or, if the Collateral is of a type
customarily sold in a recognized market or is of a type which is the subject of
widely distributed standard price quotations, at any private sale). The
Collateral Agent is authorized, in connection with any such sale, if it deems it
advisable so to do, (A) to restrict the prospective bidders on or purchasers of
any of the Pledged Securities to a limited number of sophisticated investors who
will represent and agree that they are purchasing for their own account for
investment and not with a view to the distribution or sale of any of such
Pledged Securities, (B) to cause to be placed on certificates for any or all of
the Pledged Securities or on any other securities pledged hereunder a legend to
the effect that such security has not been registered under the Securities Act
of 1933 and may not be disposed of in violation of the provision of said Act,
and (C) to impose such other limitations or conditions in connection with any
such sale as the Collateral Agent deems necessary or advisable in order to
comply with said Act or any other law. Each Pledgor will execute and deliver
such documents and take such other action as the Collateral Agent deems
necessary or advisable in order that any such sale may be made in compliance
with law. Upon any such sale the Collateral Agent shall have the right to
deliver, assign and transfer to the purchaser thereof the Collateral so sold.
Each purchaser at any such

                                       11
<PAGE>   12

sale shall hold the Collateral so sold absolutely and free from any claim or
right of whatsoever kind, including any equity or right of redemption of such
Pledgor which may be waived, and such Pledgor, to the extent permitted by law,
hereby specifically waives all rights of redemption, stay or appraisal which it
has or may have under any law now existing or hereafter adopted. The notice (if
any) of such sale required by Section 9 shall (1) in the case of a public sale,
state the time and place fixed for such sale, (2) in the case of a sale at a
broker's board or on a securities exchange, state the board or exchange at which
such sale is to be made and the day on which the Collateral, or the portion
thereof so being sold, will first be offered for sale at such board or exchange,
and (3) in the case of a private sale, state the day after which such sale may
be consummated. Any such public sale shall be held at such time or times within
ordinary business hours and at such place or places as the Collateral Agent may
fix in the notice of such sale. At any such sale the Collateral may be sold in
one lot as an entirety or in separate parcels, as the Collateral Agent may
determine. The Collateral Agent shall not be obligated to make any such sale
pursuant to any such notice. The Collateral Agent may, without notice or
publication, adjourn any public or private sale or cause the same to be
adjourned from time to time by announcement at the time and place fixed for the
sale, and such sale may be made at any time or place to which the same may be so
adjourned. In the case of any sale of all or any part of the Collateral on
credit or for future delivery, the Collateral so sold may be retained by the
Collateral Agent until the selling price is paid by the purchaser thereof, but
the Collateral Agent shall not incur any liability in the case of the failure of
such purchaser to take up and pay for the Collateral so sold and, in the case of
any such failure, such Collateral may again be sold upon like notice. The
Collateral Agent, instead of exercising the power of sale herein conferred upon
it, may proceed by a suit or suits at law or in equity to foreclose the Security
Interests and sell the Collateral, or any portion thereof, under a judgment or
decree of a court or courts of competent jurisdiction.

        SECTION 11. Expenses . Each Pledgor agrees that it will forthwith upon
demand pay to the Collateral Agent:

        (a)     the amount of any taxes which the Collateral Agent may have been
required to pay by reason of the Security Interests or to free any of the
Collateral from any Lien thereon, and

        (b)     the amount of any and all out-of-pocket expenses, including the
reasonable fees and disbursements of counsel and of any other experts, which the
Collateral Agent may incur in connection with (i) the administration or
enforcement of this Agreement, including such expenses as are incurred to
preserve the value of the Collateral and the validity, perfection, rank and
value of any Security Interest, (ii) the collection, sale or other disposition
of any of the Collateral, (iii) the exercise by the Collateral Agent of any of
the rights conferred upon it hereunder or (iv) any Default or Event of Default.

                                       12
<PAGE>   13

Any such amount not paid on demand shall bear interest at the rate applicable to
Base Rate Loans and shall be an additional Secured Obligation hereunder.

        SECTION 12. Limitation on Duty of Collateral Agent in Respect of
Collateral . Beyond the exercise of reasonable care in the custody thereof, the
Collateral Agent shall have no duty as to any Collateral in its possession or
control or in the possession or control of any agent or bailee or any income
thereon or as to the preservation of rights against prior parties or any other
rights pertaining thereto. The Collateral Agent shall be deemed to have
exercised reasonable care in the custody and preservation of the Collateral in
its possession if the Collateral is accorded treatment substantially equal to
that which it accords its own property, and shall not be liable or responsible
for any loss or damage to any of the Collateral, or for any diminution in the
value thereof, by reason of the act or omission of any Collateral Agent or
bailee selected by the Collateral Agent in good faith.

        SECTION 13. Application of Proceeds . (a) Upon the occurrence and during
the continuance of an Event of Default, the proceeds of any sale of, or other
realization upon, all or any part of the Collateral and any cash held shall be
applied by the Collateral Agent in the following order of priorities:

                        first, to payment of the expenses of such sale or other
                realization, including reasonable compensation to agents and
                counsel for the Collateral Agent, and all expenses, liabilities
                and advances incurred or made by the Collateral Agent in
                connection therewith, and any other unreimbursed expenses for
                which the Collateral Agent is to be reimbursed pursuant to any
                Financing Document and unpaid fees owing to the Collateral Agent
                under any Financing Document;

                        second, to payment of any unreimbursed expenses for
                which any Senior Secured Party is to be reimbursed pursuant to
                any Financing Document, and unpaid fees owing to the
                Administrative Agent under the New Agreement;

                        third, to the ratable payment of accrued but unpaid
                interest on the Senior Secured Obligations;

                        fourth, to the ratable payment of Senior Secured
                Obligations consisting of unpaid principal of Loans made under
                the New Agreement;

                      fifth, to the ratable payment of all other Senior Secured
               Obligations, until all such Secured Obligations have been repaid
               in full;

                                       13
<PAGE>   14

                        sixth, to the ratable payment of any unreimbursed
                expenses for which any Junior Secured Party is to be reimbursed
                pursuant to any Financing Document, unpaid fees owing to the
                Administrative Agent under the Existing Agreement and unpaid
                amount owing to the Treasury Management Bank under the Treasury
                Management Agreement which are Junior Bank Secured Obligations;

                        seventh, to the ratable payment of accrued but unpaid
                interest on the Junior Bank Secured Obligations and the NML
                Secured Obligations;

                        eighth, to the ratable payment of (x) Junior Bank
                Secured Obligations consisting of unpaid principal of Loans made
                under the Existing Agreement and, subject to the second sentence
                of subsection (b), Letter of Credit Obligations and (y) NML
                Secured Obligations;

                        ninth, to the ratable payment of all other Junior Bank
                Secured Obligations and NML Secured Obligations, until all such
                Secured Obligations have been repaid in full; and

                        finally, to payment to each Pledgor or its successors or
                assigns, or as a court of competent jurisdiction may direct, of
                any surplus then remaining from such proceeds.

        (b)     The Collateral Agent may make distributions hereunder in cash or
in kind or, on a ratable basis, in any combination thereof. If at any time any
monies collected or received by the Collateral Agent are distributable pursuant
to this Section in respect of a Letter of Credit Obligation which is a
contingent obligation at such time, then the Collateral Agent shall invest such
amounts in Liquid Investments (as defined in the Security Agreement) selected by
it and shall hold all such amounts so distributable and all such Liquid
Investments and the net proceeds thereof in trust for application to the payment
of such Letter of Credit Obligation at such time as such Letter of Credit
Obligation is no longer a contingent obligation. If the Collateral Agent holds
any amounts which were distributable in respect of any Letter of Credit
Obligations after all Letters of Credit have expired and all amounts payable
with respect thereto have been paid, such amounts shall be applied in the order
set forth in subsection (a) above.

        (c)     In making the determinations and allocations required by this
Section, the Collateral Agent shall have no liability to any Secured Party for
actions taken in reliance on information supplied by such Secured Party as to
the amounts of the Secured Obligations held by them. All distributions made by
the Collateral Agent pursuant to this Section shall be final, and the Collateral
Agent shall have no duty to inquire as to the application by any Secured Party
of any amount distributed to them. However, if at any time the Collateral Agent
determines that an allocation or

                                       14
<PAGE>   15

distribution previously made pursuant to this Section was based on a mistake of
fact (including, without limiting the generality of the foregoing, mistakes
based on any assumption that principal or interest has been paid by payments
which are subsequently recovered from the recipient thereof through the
operation of any bankruptcy, reorganization, insolvency or other laws or
otherwise), the Collateral Agent may in its discretion, but shall not be
obligated to, adjust subsequent allocations and distributions hereunder so that,
on a cumulative basis, the Collateral Agent and the other Secured Parties
receive the distributions to which they would have been entitled if such mistake
of fact had not been made.

        SECTION 14. Concerning the Collateral Agent . The provisions of Article
7 of the Credit Agreements shall inure to the benefit of the Collateral Agent in
respect of this Agreement and shall be binding upon the parties to the Credit
Agreements and the parties hereto in such respect. In furtherance and not in
derogation of the rights, privileges and immunities of the Collateral Agent
therein set forth:

        (a)     The Collateral Agent is authorized to take all such action as is
provided to be taken by it as Collateral Agent hereunder and all other action
reasonably incidental thereto. As to any matters not expressly provided for
herein (including, without limitation, the timing and methods of realization
upon the Collateral) the Collateral Agent shall act or refrain from acting in
accordance with written instructions from the Required Banks or, in the absence
of such instructions, in accordance with its discretion.

        (b)     The Collateral Agent shall not be responsible for the existence,
genuineness or value of any of the Collateral or for the validity, perfection,
priority or enforceability of the Security Interests in any of the Collateral,
whether impaired by operation of law or by reason of any action or omission to
act on its part hereunder. The Collateral Agent shall have no duty to ascertain
or inquire as to the performance or observance of any of the terms of this
Agreement by each Pledgor.

        SECTION 15. Appointment of Co-Agents . At any time or times, in order to
comply with any legal requirement in any jurisdiction, the Collateral Agent may
appoint another bank or trust company or one or more other persons, either to
act as co-agent or co-agents, jointly with the Collateral Agent, or to act as
separate agent or agents on behalf of the Secured Parties with such power and
authority as may be necessary for the effectual operation of the provisions
hereof and may be specified in the instrument of appointment (which may, in the
discretion of the Collateral Agent, include provisions for the protection of
such co-agent or separate agent similar to the provisions of Section 14).

        SECTION 16. Termination of Security Interests; Release of Collateral .
(a) Upon the repayment in full of all Secured Obligations, the termination of
the Commitments under the Credit Agreements and the cancellation or expiration
of all Letters of Credit, the Security Interests and all obligations of each
Pledgor under

                                       15
<PAGE>   16

this Agreement shall terminate and all rights to and interests in the Collateral
shall revert to such Pledgor.

        (b)     Subject to the rights of the Secured Parties hereunder if an
Event of Default shall have occurred and be continuing and subject always to the
rights of the Senior Secured Parties under the New Agreement, to the rights of
the Junior Bank Parties under the Treasury Management Agreement and the Existing
Agreement and to the rights of NML under the NML Note Agreement, upon any sale
or other disposition of any Collateral permitted under Section 5.13 of the
Existing Agreement and Section 5.13 of the New Agreement (any such sale or other
disposition, a "PERMITTED COLLATERAL SALE"), the Security Interests in the
Collateral subject to such Permitted Collateral Sale (but not in any Proceeds
thereof) shall cease immediately without any further action on the part of the
Collateral Agent. The Collateral Agent shall be fully protected in relying on a
certificate from any Pledgor stating that a sale or other disposition of any
Collateral constitutes a Permitted Collateral Sale.

        (c)     In addition to releases of Collateral effected by subsection
(b), at any time and from time to time prior to the termination of the Security
Interests, the Collateral Agent may release any of the Collateral with the prior
written consent of the Required Banks; provided that the Collateral Agent may
release all or substantially all of the Collateral (for purposes of this proviso
only, as defined in the Credit Agreements) only with the prior written consent
of all of the Banks.

        (d)     Upon the termination of the Security Interests or any release of
any Collateral effected or permitted by this Section, the Collateral Agent will
promptly, at the expense of each Pledgor, execute and deliver to such Pledgor
such documents as such Pledgor shall reasonably request to evidence the
termination of the Security Interests or the release of such Collateral, as the
case may be, including UCC termination statements, and will duly assign,
transfer and deliver to such Pledgor or to whomever lawfully shall be entitled
to receive the same, such of the Collateral as may be in the possession of the
Collateral Agent.

        (e)     Upon the repayment in full of all NML Secured Obligations, NML's
rights under this Agreement shall terminate. Upon any such termination, NML
will, at the expense of the Pledgors, execute and deliver to the Pledgors such
documents as any Pledgor may reasonably request to evidence such termination.

        SECTION 17. Notices . All notices hereunder shall be given in accordance
with Section 8.01 of the New Agreement, Section 10.01 of the Existing Agreement
or Section 9.6 of the NML Note Agreement, as the case may be.

        SECTION 18. Waivers, Non-Exclusive Remedies . No failure on the part of
the Collateral Agent to exercise, and no delay in exercising and no course of
dealing with respect to, any right under this Agreement shall operate as a
waiver thereof;

                                       16
<PAGE>   17

nor shall any single or partial exercise by the Collateral Agent of any right
under the Credit Agreement or this Agreement preclude any other or further
exercise thereof or the exercise of any other right. The rights in this
Agreement and the Credit Agreement are cumulative and are not exclusive of any
other remedies provided by law.

        SECTION 19. Successors and Assigns . This Agreement is for the benefit
of the Collateral Agent, the Secured Parties and their successors and assigns,
respectively, and in the event of an assignment of all or any of the Secured
Obligations, the rights hereunder, to the extent applicable to the indebtedness
so assigned, may be transferred with such indebtedness. This Agreement shall be
binding on each Pledgor and its successors and assigns.

        SECTION 20. Changes in Writing . Neither this Agreement nor any
provision hereof may be changed, waived, discharged or terminated orally, but
only in writing signed by each Pledgor and the Collateral Agent with the consent
of the Required Banks (or, in the case of any change to the first sentence of
Section 16 or to the number of Banks whose consent shall be required for the
Collateral Agent to take any action under this Section or any other provision of
this Agreement, the consent of all the Banks).

        SECTION 21. New York Law . This Agreement shall be construed in
accordance with and governed by the laws of the State of New York, except as
otherwise required by mandatory provisions of law and except to the extent that
remedies provided by the laws of any jurisdiction other than New York are
governed by the laws of such jurisdiction.

        SECTION 22. Severability . If any provision hereof is invalid or
unenforceable in any jurisdiction, then, to the fullest extent permitted by law,
(i) the other provisions hereof shall remain in full force and effect in such
jurisdiction and shall be liberally construed in favor of the Collateral Agent
and the Secured Parties in order to carry out the intentions of the parties
hereto as nearly as may be possible; and (ii) the invalidity or unenforceability
of any provision hereof in any jurisdiction shall not affect the validity or
enforceability of such provision in any other jurisdiction.

        SECTION 23. Restrictions on MDH . The Borrower will ensure that:

                (a)     MDH does not incur any Debt;

                (b)     MDH does not incur or suffer to exist any Lien on any of
its assets except the Lien permitted by Section 5.12(g) of each Credit
Agreement;

                (c)     MDH does not merge or consolidate with or into any other
Person;

                                       17
<PAGE>   18

                (d)     MDH does not transfer or otherwise dispose of any shares
of MDA, except pursuant to a Reduction Event;

                (e)     MDH does not engage in any business or activity
whatsoever or acquire any assets, other than the holding of the shares of MDA
owned by it on the Effective Date and the sale thereof in a Reduction Event; and

                (f)     MDH does not enter into any agreement, other than (1)
the Amended and Restated Shareholders' Agreement dated as of June 29, 2000 among
MDH and certain other shareholders of MDA, as in effect on the Effective Date,
(2) the Amended and Restated Secondary Option Agreement dated as of June 29,
2000 among MDH and certain other shareholders of MDA, as in effect on the
Effective Date, or (3) [CODE3].

        SECTION 24. Additional Pledgors . Any Subsidiary of the Borrower may
become a "Subsidiary Pledgor" party hereto and bound hereby by executing a
counterpart hereof, setting forth the address of the chief executive office of
such Pledgor, and delivering same to the Collateral Agent.

                                       18
<PAGE>   19

        IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed by their respective authorized officers as of the day and year
first above written.

                                            ORBITAL SCIENCES CORPORATION

                                            By:
                                               ---------------------------------
                                               Name:
                                               Title:

                                            ENGINEERING TECHNOLOGIES, INC.

                                            By:
                                               ---------------------------------
                                               Name:
                                               Title:

                                            ORBITAL COMMERCIAL SYSTEMS, INC.

                                            By:
                                               ---------------------------------
                                               Name:
                                               Title:

                                            MORGAN GUARANTY TRUST COMPANY
                                            OF NEW YORK, as Collateral Agent

                                            By:
                                               ---------------------------------
                                               Name:
                                               Title:

                                       19
<PAGE>   20

                                   SCHEDULE I
                                EXISTING ISSUERS

<TABLE>
<CAPTION>
                                                                                   Percentage
                                        Jurisdiction                                of Shares
                         Existing            of                       Number of    Outstanding  Certificate
      PLEDGOR             Issuer       Incorporation  Type of Shares    Shares    Being Pledged    Number
-------------------------------------------------------------------------------------------------------------
<S>                 <C>                <C>            <C>            <C>          <C>           <C>
Orbital Sciences    Engineering        Virginia       Common         354,297       100%         40
Corporation         Technologies, Inc.                Class A
                                                      Voting

                                                      Common         21,500                     12
                                                      Class B Non-
                                                      Voting
-------------------------------------------------------------------------------------------------------------
Engineering         Orbital Space      Virginia       Common         100,000      100%          1
Technologies, Inc.  Systems, Inc.
-------------------------------------------------------------------------------------------------------------
Orbital Sciences    Orbital            Virginia       Common         1,000        100%          1
Corporation         Commercial
                    Systems, Inc.
-------------------------------------------------------------------------------------------------------------
Orbital Commercial  Orbital            Virginia       Common         100          100%          1
Systems, Inc.       International,
                    Inc.
-------------------------------------------------------------------------------------------------------------
Orbital Sciences    Orbital Services   Delaware       Common         100          100%          1
Corporation         Corporation
-------------------------------------------------------------------------------------------------------------
Orbital Sciences    Orbital            Delaware       Common         100          100%          1
Corporation         Navigation
                    Corporation
-------------------------------------------------------------------------------------------------------------
Orbital Sciences    Orblink LLC        Delaware       Uncertificated N/A          100%          None
Corporation                                           membership
                                                      interest
-------------------------------------------------------------------------------------------------------------
Orbital Sciences    MDA Holdings       Delaware       Common         100          100%          1
Corporation         Corporation
-------------------------------------------------------------------------------------------------------------
Orbital Sciences    Magellan           Delaware       Common         666,666      66%           FBU 0001
Corporation         Corporation
                                                                     49,333,234                 MC 0061

                                                                     100                        7
-------------------------------------------------------------------------------------------------------------
</TABLE>

                                       20
<PAGE>   21

                                   SCHEDULE II
                             CHIEF EXECUTIVE OFFICE

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------
                   Pledgor                             Chief Executive Office Address
-----------------------------------------------------------------------------------------------
<S>                                           <C>
Orbital Sciences Corporation                  21700 Atlantic Boulevard
                                              Dulles, Virginia 20166
-----------------------------------------------------------------------------------------------
Engineering Technologies, Inc.                21700 Atlantic Boulevard
                                              Dulles, Virginia 20166
-----------------------------------------------------------------------------------------------
Orbital Commercial Systems, Inc.              21700 Atlantic Boulevard
                                              Dulles, Virginia 20166
-----------------------------------------------------------------------------------------------
</TABLE>

                                       21

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