<PAGE>   1
                                                                   EXHIBIT 10.29

                                                                [EXECUTION COPY]

                                PLEDGE AGREEMENT

     PLEDGE AGREEMENT dated as of November 30, 1999 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 (with their respective successors and
assigns, the "BANKS"), Morgan Guaranty Trust Company of New York, as
administrative agent (the "ADMINISTRATIVE AGENT") and the Collateral Agent have
entered into a Third Amended and Restated Credit Agreement dated as of December
21, 1998 (as amended from time to time, the "CREDIT AGREEMENT");

     WHEREAS, the Borrower and The Northwestern Mutual Life Insurance Company
(with its successors and assigns, "NML") have entered into a Note Agreement
dated as of June 1, 1995 (as amended from time to time, the "NML NOTE
AGREEMENT"); and

     WHEREAS, pursuant to Section 5.19(a) of the Credit Agreement and pursuant
to the NML Note Agreement, the Company and the Subsidiary Pledgors party hereto
are required to enter into a pledge agreement substantially in the form hereof;
and

     NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

     SECTION 1. Definitions. Terms defined in the Credit Agreement 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:

     "BANK SECURED OBLIGATIONS" means:




<PAGE>   2



     (x) with respect to the Company, (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 Company, whether or not allowed or allowable
as a claim in any such proceeding) on any loan to the Company under, or any note
issued by the Company pursuant to, the Credit 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 bankruptcy, insolvency or reorganization of the Company,
whether or not allowed or allowable as a claim in any such proceeding), (c) all
other amounts payable by the Company under any Financing Document, and (d) 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 that certain
waiver and consent letter dated as of November 30, 1999.

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

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

     "EXCLUDED MAGELLAN NOTE" means the Amended and Restated Unsecured
Subordinated Revolving Promissory Note dated November 29, 1999 in the principal
amount of $22,470,846.00 issued by Magellan to the Company.

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

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

     "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 Credit 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.





                                       2
<PAGE>   3



     "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

          (y) with respect to each Subsidiary Pledgor, all obligations of such
Subsidiary Pledgor incurred by such Subsidiary Pledgor pursuant to the NML
Guaranty Agreement.

     "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).

     "SECURED OBLIGATIONS" means:

     (x) with respect to the Company, (a) the Bank Secured Obligations of the
Company and (b) the NML Secured Obligations of the Company; and

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

     "SECURED PARTIES" means each of the Banks, the Agents and NML.

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





                                       3
<PAGE>   4



     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.
     Other than with respect to MacDonald Dettwiler Holdings Inc., 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 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





                                       4
<PAGE>   5



     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.

     SECTION 3. The Security Interests. In order to secure the full and punctual
payment of the Secured Obligations in accordance with the terms thereof, and to
secure the performance of all the obligations of each Pledgor hereunder:

          (a) Each Pledgor hereby assigns and pledges to and with the Collateral
     Agent for the benefit of the Secured Parties and grants to the Collateral
     Agent for the benefit of the 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"). Contemporaneously with the execution and delivery hereof,
     such Pledgor is delivering certificates representing the Pledged Securities
     held by such Pledgor in pledge hereunder (other than any Pledged Stock not
     evidenced by certificates).

          (b) 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 Company (including any New Issuer) owes any
     Debt to any Pledgor, such Pledgor will within 10 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





                                       5
<PAGE>   6



     Pledgor will not be required to take the actions described in this
     subsection (b) 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, (2)
     such Pledgor will not be required to take any of the actions described in
     this subsection (b) with respect to the capital stock, limited 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 and (3)
     the Company shall not be required to pledge the Excluded Magellan Note. All
     such shares and other equity interests, notes and instruments constitute
     Pledged Securities and are subject to all provisions of this Agreement.

          (c) 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,





                                       6
<PAGE>   7



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.

     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 Banks and NML 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.





                                       7
<PAGE>   8



     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 Banks, NML or otherwise,
for the sole use and benefit of the Collateral Agent, the Banks and NML, 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,

          (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





                                       8
<PAGE>   9



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 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




                                       9
<PAGE>   10



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.

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





                                       10
<PAGE>   11



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, the
     Administrative Agent, any Bank or NML is to be reimbursed pursuant to
     the Credit Agreement or the NML Note Agreement, as the case may be,
     and unpaid fees owing to the Agents under the Credit Agreement;

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

          third, to the ratable payment of (x) the Bank Secured Obligations
     consisting of unpaid principal of Loans and, subject to the second
     sentence of subsection (B), Letter of Credit Obligations and (y) the
     NML Secured Obligations;

          fourth, to the ratable payment of all other Bank Secured
     Obligations and NML Secured Obligations, until all such Secured
     Obligations shall have been paid 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 Company
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





                                       11
<PAGE>   12



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 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 Agreement shall inure to the benefit of the Collateral Agent in
respect of this Agreement and shall be binding upon the parties to the Credit
Agreement 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.





                                       12
<PAGE>   13



     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 Banks and NML 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 Bank Secured Obligations, the termination of
the Commitments under the Credit Agreement and the cancellation or expiration of
all Letters of Credit, the Security Interests shall terminate and all rights to
the Collateral shall revert to each Pledgor. At any time and from time to time
prior to such 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
Agreement) only with the prior written consent of all the Banks. Upon any such
termination of the Security Interests or release of Collateral, the Collateral
Agent will, at the expense of such 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.

     (b) 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 10.01 of the Credit 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; 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.



                                       13
<PAGE>   14

     SECTION 19. Successors and Assigns. This Agreement is for the benefit of
the Collateral Agent, the Banks and NML 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,
the Banks and NML 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. Guaranty. Each Subsidiary Pledgor hereby agrees to be bound by
the provisions of Article 9 of the Credit Agreement and to be subject to all of
the obligations of a "Guarantor" thereunder, and the limitations set forth in
Section 9.05 of the Credit Agreement shall apply to such obligations of such
Subsidiary Pledgor.

     SECTION 24. Additional Pledgors. Any Subsidiary of the Company 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.



                                       14
<PAGE>   15


     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:



                                       15
<PAGE>   16



                              THE NORTHWESTERN MUTUAL LIFE
                                 INSURANCE COMPANY

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


                                       16
<PAGE>   17



                                   SCHEDULE I
                                EXISTING ISSUERS

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------
PLEDGOR                EXISTING                JURISDICTION      TYPE OF          NUMBER      PERCENTAGE      CERTIFICATE
                       ISSUER                  OF                SHARES           OF          OF SHARES       NUMBER
                                               INCORPORATION                      SHARES      OUTSTANDING
                                                                                              BEING
                                                                                              PLEDGED

<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%            4
Technologies, Inc.     Systems, Inc.

------------------------------------------------------------------------------------------------------------------
Orbital Sciences       Orbital                 Virginia          Common           1,000       100%            1
Corporation            Commercial
                       Systems, Inc.

------------------------------------------------------------------------------------------------------------------
Orbital                Orbital                 Virginia          Common           100         100%            1
Commercial             International, Inc.
Systems, Inc.

------------------------------------------------------------------------------------------------------------------
Orbital Sciences       Orbital Services        Delaware          Common           100         100%            1
Corporation            Corporation
------------------------------------------------------------------------------------------------------------------
</TABLE>

                                       17
<PAGE>   18





<TABLE>
<S>                  <C>               <C>          <C>                <C>     <C>     <C>
----------------------------------------------------------------------------------------------
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     MacDonald         Canada       Common             666     66%      C-4
Corporation          Dettwiler
                     Holdings Inc.
----------------------------------------------------------------------------------------------
</TABLE>


                                       18
<PAGE>   19


                                   SCHEDULE II
                             Chief Executive Office

<TABLE>
<S>                                  <C>
--------------------------------------------------------------------
Pledgor                              Chief Executive Office Address

--------------------------------------------------------------------
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>


                                       19