Document:

<PAGE>   1

                                                                    Exhibit 10.2

                               AMENDMENT NO. 10
                                      TO
                          THIRD AMENDED AND RESTATED
                      CREDIT AND REIMBURSEMENT AGREEMENT

       AMENDMENT No. 10 dated as of June 7, 2000 among ORBITAL SCIENCES
CORPORATION (the "COMPANY"), the BANKS listed on the signature pages hereof and
MORGAN GUARANTY TRUST COMPANY OF NEW YORK, as Administrative Agent (the
"ADMINISTRATIVE AGENT") and as Collateral Agent (the "COLLATERAL AGENT").

                                   WITNESSETH:

       WHEREAS, the parties hereto have heretofore entered into a Third Amended
and Restated Credit and Reimbursement Agreement dated as of December 21, 1998
(as amended from time to time, the "CREDIT AGREEMENT"); and

       WHEREAS, the Company and the Banks wish to amend the Credit Agreement as
set forth herein;

       NOW, THEREFORE, the parties hereto agree as follows:

       SECTION 1. Definition; References. Unless otherwise specifically defined
herein, each term used herein that is defined in the Credit Agreement shall have
the meaning assigned to such term in the Credit Agreement. Each reference to
"hereof", "hereunder", "herein" and "hereby" and each other similar reference
and each reference to "this Agreement" and each other similar reference
contained in the Credit Agreement shall from and after the Amendment No. 10
Effective Date (as defined in Section 20 below) refer to the Credit Agreement as
amended hereby.

       SECTION 2. Amendments to the Definitions. (a) Section 1.01 of the Credit
Agreement is amended by adding therein the following definitions in alphabetical
order:

       "ADDITIONAL DEBT DATE" means the first date on or after the Amendment No.
10 Effective Date on which the Company or any of its wholly-owned domestic
Subsidiaries shall have consummated one or more Debt Issuances pursuant to which
Debt in an aggregate principal or face amount at least equal to $100,000,000
shall have been issued.

<PAGE>   2

       "AMENDMENT NO. 10 EFFECTIVE DATE" means the date of effectiveness of
Amendment No. 10 to this Agreement.

       "COOLER ACQUISITION" means the acquisition by the Company from Thermo
Electron Corporation of all of the issued and outstanding common stock of
Coleman Research Corporation or all or substantially all of its assets
substantially on the terms set forth in the Letter of Intent, dated March 16,
2000 between the Company and Thermo Electron Corporation provided by the Company
to the Banks prior to the Amendment No. 10 Effective Date.

       "COOLER ACQUISITION DATE" means the date of consummation of the Cooler
Acquisition.

       "MDA SHARE SALE" means the sale or other disposition of shares of common
stock of MDA pursuant to a registered offering substantially on the terms
described by the Company to the Banks prior to the Amendment No. 10 Effective
Date.

       (b) The following definition set forth in Section 1.01 of the Credit
Agreement is amended to read in its entirety as follows:

       "EARNINGS AVAILABLE FOR FIXED CHARGES" means, for any period,
Consolidated Net Income for such period (excluding therefrom (i) any
extraordinary items of gain or loss, (ii) any gain or loss of any other Person
accounted for pursuant to the equity method, except in the case of gain to the
extent of cash distributions received from such Person during the relevant
period), plus the aggregate amounts deducted in determining Consolidated Net
Income for such period in respect of (i) interest and rental expense, (ii)
income taxes, (iii) write-offs with respect to the investment made by the
Company in CCI International N.V. for any fiscal quarter ended prior to December
31, 1999, up to an aggregate amount equal to $21,400,000, (iv) Excluded Charges,
up to an aggregate amount equal to $5,000,000, (v) one-time accounting charges
resulting in adjustments to earnings for each of the fiscal quarters of the
fiscal year ended December 31, 1998, up to an aggregate amount equal to
$35,600,000 and (vi) non-cash asset impairment charges incurred on or prior to
December 31, 1999 up to an aggregate amount equal to $17,027,000, non-cash
write-downs up to an aggregate amount equal to $14,820,000 incurred on or prior
to December 31, 1999 and other non-cash charges similar to depreciation and
amortization (but not including depreciation or amortization).

       SECTION 3. Increase in Commitment Reduction and Mandatory Prepayments
Under Certain Circumstances. (a) Section 2.10(d) of the Credit Agreement is
amended by inserting the phrase ", subject to the provisions of

                                       2
<PAGE>   3

subsection (f)(iii) below" immediately after the words ";provided that"
contained therein.

       (b) Section 2.10(e) of the Credit Agreement is amended by inserting the
phrase "subject to subsection (f)(ii) below," immediately before the words "the
Commitments" contained therein.

       (c) Section 2.10(f) of the Credit Agreement is hereby redesignated as
Section 2.10(g) thereof.

       (d) A new Section 2.10(f) to the Credit Agreement is added immediately
after Section 2.10(e) thereof, to read in its entirety as follows:

                     (f) (i) If the Cooler Acquisition Date has occurred and the
              Additional Debt Date has not occurred on or prior to the Cooler
              Acquisition Date, then on the Cooler Acquisition Date the
              Commitments shall be automatically and ratably reduced by an
              aggregate amount equal to $10,000,000 (in addition to any
              reduction of the Commitments that may be effected on the Cooler
              Acquisition Date pursuant to subsections (d) or (e) above).

                     (ii) If the Cooler Acquisition Date has occurred on or
              prior to any date set forth below and the Additional Debt Date has
              not occurred on or prior to the Cooler Acquisition Date, then to
              the extent not theretofore reduced to the same or a lesser amount,
              the Commitments shall be automatically and ratably reduced on each
              date set forth below to the aggregate amount set forth opposite
              such dates:

<TABLE>
<CAPTION>
           ------------------------------------------------------------------------
                    DATE                              AGGREGATE AMOUNT
           ------------------------------------------------------------------------
           <S>                                  <C>
                    August 1, 2000                    $115,000,000
           ------------------------------------------------------------------------
                    July 1, 2001                      $75,000,000
           ------------------------------------------------------------------------
</TABLE>

                     (iii) If the Cooler Acquisition Date has occurred and the
              Additional Debt Date has not occurred on or prior to the Cooler
              Acquisition Date, then (i) the aggregate amount of the reduction
              of the Commitments effected pursuant to Section 2.10(d) as a
              result of Reduction Events consummated on or before August 1, 2000
              shall not exceed $50,000,000, (ii) the aggregate amount of the
              reduction of the Commitments effected pursuant to Section 2.10(d)
              as a result of Reduction Events consummated after August 1, 2000
              shall not exceed $30,000,000 and (iii) in no event shall the
              Commitments be reduced pursuant to Section 2.10(d) below
              $75,000,000.

                                       3
<PAGE>   4

       (e) New Sections 2.10(h) and 2.10(i) are added immediately after Section
2.10(g) of the Credit Agreement, to read in their entirety as follows:

                     (h) If the Cooler Acquisition Date has occurred and the
              Additional Debt Date has not occurred on or prior to the Cooler
              Acquisition Date, then on the Cooler Acquisition Date, in addition
              to any prepayment of the Loans to be made by the Borrowers
              pursuant to Section 2.10(f), the Borrowers shall prepay, together
              with accrued interest thereon, Loans in an aggregate principal
              amount equal to $10,000,000. Any prepayment of the Loans made
              pursuant to this subsection (h) shall not cause any reduction of
              the Commitments.

                     (i) Each prepayment of the Loans made by the Borrowers
              pursuant to this Section 2.10 shall be applied to prepay such
              Group or Groups of Loans as the Borrowers shall designate (or,
              absent any such designation, as the Administrative Agent shall
              determine), and shall be applied to prepay ratably the Loans of
              the several Banks included in each such Group or Groups of Loans.

       SECTION 4. Limitation on New Extensions of Credit. (a) The following
phrase is added at the end of Section 2.01 of the Credit Agreement: ",subject to
the provisions of Sections 2.02(e) and 2.02(f).".

       (b) New Sections 2.02(e) and (f) to the Credit Agreement are added
immediately after Section 2.02(d) thereof, to read in their entirety as follows:

                     (e) The Company agrees that, except as permitted in
              subsection (f) below, on and after the Amendment No. 10 Effective
              Date, neither Company nor any other Borrower shall deliver a
              Notice of Borrowing or a request for issuance of a Letter of
              Credit or otherwise request any Bank (including the LC Bank) to
              extend any credit to the Company or any other Borrower, and that,
              notwithstanding any other provision hereof, on and after the
              Amendment No.10 Effective Date, no Bank (including the LC Bank)
              shall be required to make any Loan, or issue or participate in any
              Letter of Credit (it being understood that nothing in this
              sentence shall be construed to prohibit the Company from
              delivering a Notice of Interest Rate Election with respect to any
              Loan outstanding prior to the Amendment No. 6 Effective Date or
              any Loan made on or after the Cooler Acquisition Date and
              permitted to be made pursuant to subsection (f) below and
              continuing or converting any such Loan on the terms set forth in
              such Notice of Interest Rate Election).

                                       4
<PAGE>   5

                     (f) If the Cooler Acquisition Date has occurred and the
              Additional Debt Date has not occurred on or prior to the Cooler
              Acquisition Date and the Borrowers shall have complied with their
              obligations under Section 2.10(h), the Company or any other
              Borrower may deliver a Notice of Borrowing or request for issuance
              of a Letter of Credit, on any date (a "test date") on or after the
              Cooler Acquisition Date, and the Banks (including the LC Bank)
              shall be required to make such requested Loan, or issue or
              participate in such requested Letter of Credit (subject to
              satisfaction of the conditions set forth in Section 3.03 and, if
              applicable, Section 3.04); provided that after giving effect to
              any such Loan or issuance of or participation in any such Letter
              of Credit, the portion of the total Exposure of all the Banks that
              has been incurred on or after the Cooler Acquisition Date and that
              is outstanding on such test date shall not exceed $10,000,000 (it
              being understood that nothing in this sentence shall be construed
              to prohibit the Company from delivering a Notice of Interest Rate
              Election with respect to any Loan outstanding prior to the
              Amendment No. 6 Effective Date or any Loan permitted to be made
              pursuant to this subsection (f) and continuing or converting any
              such Loan on the terms set forth in such Notice of Interest Rate
              Election).

       (c) The following phrase is added at the beginning of Section 2.03 of the
Credit Agreement: "Subject to the provisions of Sections 2.02(e) and 2.02(f),".

       (d) Section 3.03 of the Credit Agreement is amended by:

                (i) deleting the "and" at the end of clause (c) thereof;

               (ii) deleting the period at the end of clause (d) thereof and
       substituting it with ";and"; and

              (iii) inserting new clauses (e) and (f) immediately after clause
       (d) thereof to read in their entirety as follows:

                     (e) (A) the Cooler Acquisition Date shall have occurred and
              the Additional Debt Date shall not have occurred on or prior to
              the Cooler Acquisition Date and (B) after giving effect to such
              Credit Event (and the application of the proceeds thereof), the
              portion of the total Exposure of all the Banks that has been
              incurred on or after the Cooler Acquisition Date and that is
              outstanding on such date does not exceed $10,000,000; and

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<PAGE>   6

                     (f) the Borrowers shall have complied with their
              obligations under Sections 2.10(g) and 2.10(h).

       SECTION 5. Amendment of the Investments Covenant To Permit the Cooler
Acquisition. Section 5.07 of the Credit Agreement is amended by:

                (i) deleting the "and" at the end of clause (o) thereof,

               (ii) renumbering clause (p) thereof as clause (q) and
       substituting a reference to "clause (q)" for the reference to "clause
       (p)" contained therein;

              (iii) adding a new clause (p) immediately after clause (o)
       thereof, to read in its entirety as follows:

                     (p)    Investments consisting of the acquisition of capital
              stock of Coleman Research Corporation constituting the
              consummation of the Cooler Acquisition; provided that (i) such
              Investments are made after the Amendment No. 10 Effective Date and
              after the date on which the Company and its wholly-owned domestic
              Subsidiaries shall have generated aggregate cash proceeds of not
              less than $140,000,000 consisting of (A) Net Cash Proceeds
              generated by any one or more (x) Asset Sales (other than the MDA
              Share Sale) which would reduce Consolidated EBITDA by less than
              the expected increase in Consolidated EBITDA resulting from the
              Cooler Acquisition, (y) Debt Issuances, and/or (z) Equity
              Issuances, and/or (B) not more than $40,000,000 in aggregate cash
              proceeds resulting from (x) Net Cash Proceeds from the MDA Share
              Sale, and/or (y) cash proceeds from any one or more sale/leaseback
              transactions, asset based financing and/or other issuances of Debt
              not constituting Debt Issuances, (ii) the aggregate amount of cash
              consideration paid by the Company and its Subsidiaries with
              respect to the Cooler Acquisition does not exceed $38,000,000,
              (iii) the aggregate value of the stock of the Company issued as
              consideration with respect to the Cooler Acquisition does not
              exceed $38,000,000, (iv) neither the Company nor any of its
              Subsidiaries shall pay any consideration with respect to the
              Cooler Acquisition, except the consideration described in clauses
              (ii) and (iii) of this proviso and (v) on the Cooler Acquisition
              Date, the Borrowers shall comply with their obligations under
              Sections 2.10(g) and (h); and

               (iv) amending the last sentence thereof to read in its entirety
       as follows:

                                       6
<PAGE>   7

                     Notwithstanding any provision of this Agreement (including
              the foregoing clauses of this Section 5.07) (x) after the
              Amendment No. 8 Effective Date and prior to the Amendment No.10
              Effective Date, the Company will not and will not permit any
              Subsidiary to, consummate any acquisition of any other Person or
              all of the components of an entire line of business or division of
              any other Person (whether by purchase of stock or assets, by
              merger, consolidation or otherwise) without the prior written
              consent of the Required Banks, other than the DataQuick
              Acquisition and (y) on and after the Amendment No.10 Effective
              Date, the Company will not and will not permit any Subsidiary to,
              consummate any acquisition of any other Person or all of the
              components of an entire line of business or division of any other
              Person (whether by purchase of stock or assets, by merger,
              consolidation or otherwise) without the prior written consent of
              the Required Banks, other than the DataQuick Acquisition and the
              Cooler Acquisition.

       SECTION 6. Change in the Minimum Net Worth Covenant. Section 5.08 of the
Credit Agreement is amended to read in its entirety as follows:

                     SECTION 5.08. Minimum Consolidated Net Worth. Consolidated
              Net Worth at the last day of any fiscal quarter set forth below
              will not be less than (i) the amount set forth in the table below
              opposite such fiscal quarter plus (ii) 50% of Consolidated Net
              Income for each fiscal quarter of the Company ended after March
              31, 2000, which such Consolidated Net Income is positive (but with
              no deduction on account of any fiscal quarter for which
              Consolidated Net Income is negative) plus (iii) 100% of the
              aggregate amount by which Consolidated Net Worth shall have been
              increased by reason of the issuance and sale after March 31, 2000
              and on or prior to such date of any capital stock or the
              conversion or exchange of any Debt of the Company into or with
              capital stock of the Company consummated after March 31, 2000 and
              on or prior to such date.

<TABLE>
<CAPTION>
           ------------------------------------------------------------------------
              FISCAL QUARTER ENDED                      AMOUNT
           ------------------------------------------------------------------------
           <S>                               <C>
              6/30/00                                   $225,000,000
           ------------------------------------------------------------------------
              9/30/00                                   $200,000,000
           ------------------------------------------------------------------------
              12/31/00                                  $190,000,000
           ------------------------------------------------------------------------
</TABLE>

                                       7
<PAGE>   8

<TABLE>
<CAPTION>
           ------------------------------------------------------------------------
              FISCAL QUARTER ENDED                      AMOUNT
           ------------------------------------------------------------------------
           <S>                               <C>
              3/31/01                                   $175,000,000
           ------------------------------------------------------------------------
              6/30/01                                   $165,000,000
           ------------------------------------------------------------------------
              9/30/01                                   $190,000,000
           ------------------------------------------------------------------------
              12/31/01 and thereafter                   $190,000,000
           ------------------------------------------------------------------------
</TABLE>

       SECTION 7. Change in the Leverage Ratio and the Senior Leverage Ratio.
Section 5.09 of the Credit Agreement is amended to read in its entirety as
follows:

                     SECTION 5.09. (a) Leverage. The Consolidated Leverage Ratio
              will at no date during any period set forth below exceed the ratio
              set forth in Column I below opposite such period (or, if the
              Additional Debt Date shall have occurred on or prior to the last
              day of such period, the ratio set forth in Column II below
              opposite such period):

<TABLE>
<CAPTION>
         -------------------------------------------------------------------------------
         PERIOD                                COLUMN I                COLUMN II
         -------------------------------------------------------------------------------
         <S>                                 <C>                    <C>
         Amendment No. 10                      4.70:1                  4.85:1
         Effective Date - 6/30/00
         -------------------------------------------------------------------------------
         7/1/00-9/30/00                        4.85:1                  5.50:1
         -------------------------------------------------------------------------------
         10/1/00-12/31/00                      4.85:1                  6.30:1
         -------------------------------------------------------------------------------
         1/1/01-3/31/01                        4.50:1                  6.00:1
         -------------------------------------------------------------------------------
         4/1/01-6/30/01                        4.50:1                  5.35:1
         -------------------------------------------------------------------------------
         7/1/01-9/30/01                        3.00:1                  3.75:1
         -------------------------------------------------------------------------------
         10/1/01 and thereafter                3.00:1                  3.75:1
         -------------------------------------------------------------------------------
</TABLE>

       (b)    Senior Leverage. The Senior Leverage Ratio will at no date during
any period set forth below exceed the ratio set forth below opposite such
period:

<TABLE>
<CAPTION>
         --------------------------------------------------------------------------------
                  PERIOD                                    RATIO
         --------------------------------------------------------------------------------
         <S>                                      <C>
         Amendment No. 10 Effective Date -         3.5:1
         6/30/00
         --------------------------------------------------------------------------------
</TABLE>

                                       8
<PAGE>   9

<TABLE>
         <S>                                      <C>
         --------------------------------------------------------------------------------
         7/1/00- 9/30/00                           3.1:1
         --------------------------------------------------------------------------------
         10/1/00- 12/31/00                         3.5:1
         --------------------------------------------------------------------------------
         1/1/01-6/30/01                            3.0:1
         --------------------------------------------------------------------------------
         7/1/01 and thereafter                     2.0:1
         --------------------------------------------------------------------------------
</TABLE>

       SECTION 8. Change in the Consolidated Fixed Charge Ratio. Section 5.10 of
the Credit Agreement is amended to read in its entirety as follows:

                     SECTION 5.10. Consolidated Fixed Charge Ratio. At the last
              day of any fiscal quarter set forth below, the ratio of Earnings
              Available for Fixed Charges to Consolidated Fixed Charges, in each
              case for the four consecutive fiscal quarters then ended, will not
              be less than the ratio set forth in Column I below opposite such
              fiscal quarter (or, if the Additional Debt Date shall have
              occurred on or prior to the last day of such fiscal quarter, the
              ratio set forth in Column II below opposite such fiscal quarter):

<TABLE>
<CAPTION>
         -----------------------------------------------------------------------------------
         FISCAL QUARTER ENDED                 COLUMN 1               COLUMN II
         -----------------------------------------------------------------------------------
         <S>                              <C>                   <C>
         6/30/00                              1.15:1                 1.15:1
         -----------------------------------------------------------------------------------
         9/30/00                              1.15:1                 1.15:1
         -----------------------------------------------------------------------------------
         12/31/00                             0.85:1                 0.75:1
         -----------------------------------------------------------------------------------
         3/31/01                              1.00:1                 0.75:1
         -----------------------------------------------------------------------------------
         6/30/01                              1.10:1                 0.75:1
         -----------------------------------------------------------------------------------
         9/30/01                              1.75:1                 1.50:1
         -----------------------------------------------------------------------------------
         12/31/01 and thereafter              1.75:1                 1.50:1
         -----------------------------------------------------------------------------------
</TABLE>

       SECTION 9. Additional Exception for Negative Pledge. Section 5.14 of the
Credit Agreement is amended by (i) deleting the "and" at the end of clause (t)
thereof, (ii) renumbering clause (u) thereof as clause (v), and (iii) adding a
new clause (u) immediately after clause (t) thereof, to read in its entirety as
follows:

                     (u)    Liens on the shares of MDA pursuant to Section 13 of
              the Secondary Option Agreement contemplated by the MDA Transaction
              Agreement; and

                                       9
<PAGE>   10

       SECTION 10. Amendment of the Subsidiary Debt Covenant and the MDA
Covenant. Section 5.17 of the Credit Agreement is amended to read in its
entirety as follows:

                     SECTION 5.17. Subsidiary Debt. (a) Total Debt of all of the
              Company's Subsidiaries (excluding (i) Loans and Letter of Credit
              Liabilities hereunder and any Guarantees thereof, (ii) Debt of a
              Subsidiary to the Company or to a Wholly-Owned Subsidiary of the
              Company, (iii) Debt of MDA or any of its Subsidiaries and (iv) any
              Guarantees of the NML Debt) will at no time on or after the
              Amendment No. 10 Effective Date exceed 5% of Consolidated Net
              Worth. For purposes of this subsection (a), any preferred stock of
              a Subsidiary held by a Person other than the Company or a
              Wholly-Owned Subsidiary of the Company shall be included, at the
              higher of its voluntary or involuntary liquidation value, in the
              "Debt" of such Subsidiary.

                     (b)    MDA Equity. On and after the Amendment No. 8
              Effective Date, the Company will cause MDA to comply with the
              covenant set forth in the Credit Agreement evidencing the MDA
              Financing requiring MDA to maintain a minimum consolidated equity
              level; provided that failure by the Company to comply with this
              subsection (b) at any time shall not constitute an Event of
              Default hereunder unless at such time such failure by MDA to
              comply with such covenant in such Credit Agreement constitutes an
              event of default thereunder which has not been waived by the
              lenders to the MDA Financing.

       SECTION 11. Change in Consolidated Capital Expenditures. Section 5.20 of
the Credit Agreement is hereby amended to read in its entirety as follows:

                     SECTION 5.20. Consolidated Capital Expenditures. At any
              date on or after the Amendment No. 10 Effective Date the aggregate
              amount of Consolidated Capital Expenditures (i) for the period
              from and including January 1, 2000 to and including December 31,
              2000 (other than the DataQuick Acquisition and the Cooler
              Acquisition, to the extent either constitutes Consolidated Capital
              Expenditures) will not exceed $60,700,000, (ii) for the period
              from and including January 1, 2001 to and including December 31,
              2001 will not exceed $50,000,000 and (iii) for the period from and
              including January 1, 2002 to and including December 31, 2002 will
              not exceed $50,000,000.

                                       10
<PAGE>   11

       SECTION 12. Release of Amounts in the Restricted Account. (a) A new
Section 5.24 is added immediately after Section 5.23 of the Credit Agreement, to
read in its entirety as follows:

                     SECTION 5.24. Restricted Account. (a) Releases. The
              Borrowers and the Banks agree that amounts on deposit in the
              Restricted Account (other than amounts deposited therein pursuant
              to Section 2.10(d)) shall be released therefrom from time to time
              upon request of the Company, so long as at the time no Default
              shall have occurred and be continuing, as follows: (A) upon
              consummation of the security arrangements contemplated by Section
              5.19(d) of the Credit Agreement, $5,000,000 shall be released; (B)
              on the date on which the aggregate amount of the Commitments shall
              have been reduced to $150,000,000 or less, so long as the
              Additional Debt Date shall not have occurred on or prior to such
              date, $10,000,000 shall be released; (C) if no amounts have been
              released pursuant to clause (B) or if the full amount required to
              be deposited pursuant to subsection (b) has been so deposited, on
              the date on which the aggregate amount of the Commitments shall
              have been reduced to $85,000,000 (or, if the Cooler Acquisition
              Date shall have occurred and the Additional Debt Date shall not
              have occurred on or prior to the Cooler Acquisition Date,
              $75,000,000) or less, $10,000,000 shall be released; (D) amounts
              deposited therein (including pursuant to subsection (b)) not
              theretofore released pursuant to clauses (A), (B) and (C) shall be
              released from time to time, so long as after giving effect to such
              release the Company's cash balances do not exceed $10,000,000 and
              (E) any such request for release shall be accompanied by a
              certificate signed by a duly authorized officer of the Company (on
              which the Collateral Agent may conclusively rely) to the effect
              that the applicable conditions set forth above have been satisfied
              in connection with such release.

                     (b)    Deposits. On the Additional Debt Date, the Borrowers
              shall deposit in the Restricted Account an amount equal to
              $10,000,000; provided that the Borrowers shall not be required to
              deposit any such amount (i) unless prior to the Additional Debt
              Date, amounts on deposit in the Restricted Account shall have been
              released pursuant to clause (B) of subsection (a) above or (ii) if
              on the Additional Debt Date the aggregate amount of the
              Commitments does not exceed (x) if the Cooler Acquisition Date has
              occurred and the Additional Debt Date has not occurred on or prior
              to the Cooler Acquisition Date, $75,000,000, (y) otherwise
              $85,000,000.

                                       11
<PAGE>   12

       (b) The Borrowers and the Banks agree that the provisions set forth in
Section 5(d) of Amendment No. 6 to the Credit Agreement dated as of December 21,
1999 regarding the release of amounts on deposit in the Restricted Account shall
cease to be in effect on and as of the Amendment No. 10 Effective Date.

              SECTION 13. Additional Events of Default. (a) Section 6.01(c) of
the Credit Agreement is amended to read in its entirety as follows:

                     (c)    any Borrower shall fail to observe or perform any
              covenant or agreement contained in Sections 5.01(g), 5.07 to 5.22
              inclusive and Section 5.24;

       (a) A new Section 6.01(n) to the Credit Agreement is added immediately
after Section 6.01(m) thereof, to read in its entirety as follows:

                     (n)    the Company or any other Borrower shall deliver a
              Notice of Borrowing or a request for issuance of a Letter of
              Credit or otherwise request any Bank to extend any credit to the
              Company or any other Borrower under the Credit Agreement, except
              as permitted pursuant to Section 2.02(f);

       SECTION 1. Amendment to Pricing Schedule. The Pricing Schedule to the
Credit Agreement is amended by substituting the date "December 21, 2002" for the
date "January 1, 2001" set forth in paragraph immediately after the table set
forth therein.

       SECTION 2. Release of Lien on Certain MDA Shares. (a) The Banks hereby
agree that, in the event the Company consummates the MDA Share Sale (as defined
in the Credit Agreement as amended hereby) at any time prior to the delivery by
the Company to the Collateral Agent of all of the capital stock of New MDH (as
defined in Amendment No. 6 to the Credit Agreement), the Lien on such shares so
sold or otherwise transferred (the "MDA SUBJECT SHARES") (including all proceeds
thereof other than proceeds thereof which must be paid to the Banks pursuant to
Section 15(a)(ii)) shall be released upon and subject to the following terms and
conditions:

              (i) the MDA Subject Shares shall constitute no more than 14.67% of
       the aggregate amount of shares of MDA held directly or indirectly by the
       Company;

              (ii) on the date of consummation of the MDA Share Sale (the "MDA
       SHARE SALE DATE"), the Borrowers shall comply with their obligations
       under Section 2.10(g) of the Credit Agreement; and

                                       12
<PAGE>   13

              (iii) the Company shall have delivered to the Administrative Agent
       and the Collateral Agent a certificate, dated the MDA Share Sale Date,
       duly executed by the chief financial officer of the Company and
       certifying that the terms and conditions set forth in clauses (i) and
       (ii) of this Section 15(a) shall have been complied with on and as of the
       MDA Share Sale Date.

       The Company agrees that failure to satisfy the conditions set forth in
clauses (i) through (iii), inclusive, of this Section 15(a) in the event the
Company consummates the MDA Share Sale pursuant to a registered offering
substantially on the terms described by the Company to the Banks prior to the
Amendment No. 10 Effective Date shall constitute an Event of Default.

       (a) The Company agrees to cause the conditions set forth in clauses (i)
through (iii), inclusive, of Section 15(a) to be satisfied in the event that the
MDA Share Sale is consummated at any time on or after the delivery to the
Collateral Agent of all of the capital stock of New MDH and agrees that any
failure to do so shall constitute an Event of Default.

       (b) The Banks hereby authorize the Collateral Agent to execute any
release instruments to evidence the release of the Lien on the MDA Shares (and
the portion of the proceeds thereof which are not required to be paid to the
Banks pursuant to Section 15(a)(ii) above) effected pursuant to subsection (a)
of this Section 15. In doing so, the Collateral Agent shall be entitled to rely
fully on the certificate described in clause (iii) of Section 15(a), and shall
have no obligation to independently verify whether the Company shall have
complied with the terms and conditions set forth in Section 15(a). For the
avoidance of doubt, the Banks and the Company acknowledge and agree that,
without limiting any other rights that the Company may have, in no event shall
the terms of this Section 15 affect the agreements set forth in Sections 5(c),
5(f) or 5(g) of Amendment No. 6 to Credit Agreement, which shall continue to
remain in full force and effect on and after the Amendment No. 10 Effective
Date.

       (d) The Company agrees that on and after the date on which the Company
delivers to the Collateral Agent all of the capital stock of New MDH, the
Company will not permit New MDH to transfer any of the shares of capital stock
of MDA held by New MDH to any other Subsidiary of the Company other than to a
Subsidiary (i) which is a Subsidiary Guarantor, (ii) which is incorporated in
the United States, (iii) which does not owe any Debt to any Person other than to
any Borrower or Subsidiary Guarantor, and (iv) all of the capital stock of which
has been subjected to a Lien on substantially the same terms as the Lien granted
over the capital stock of New MDH as of such date, and agrees that any failure
to

                                       13
<PAGE>   14

comply with the provisions of this subsection (d) shall constitute an Event of
Default.

       SECTION 3. Covenants and Waivers Prior to Amendment No. 10 Effective
Date. (a) The Banks and the Company hereby acknowledge and agree that the
amendments set forth in this Amendment No. 10 to Credit Agreement, including,
without limitation, the amendments to Sections 5.08, 5.09, 5.10 and 5.17, are
intended to amend the Credit Agreement only in respect of the time periods
occurring after the Amendment No. 10 Effective Date, and in no event shall such
amendments retroactively amend or alter the provisions of the Credit Agreement
which were in effect prior to the Amendment No. 10 Effective Date.

       (b) The Banks and the Company acknowledge and agree that, with respect to
the waivers granted pursuant to Section 3(a) of Amendment No. 8 to Credit
Agreement (the "EXISTING WAIVERS") (i) at no time shall any failure of the
Company to comply with any Section of the Credit Agreement specified in the
Existing Waivers constitute an Event of Default if such failure occurred prior
to the Amendment No. 10 Effective Date, (ii) in no event shall the Existing
Waivers be subject to revocation, (iii) the Waiver Period (as defined in
Amendment No. 8 to the Credit Agreement) with respect to the Existing Waivers
shall terminate on the Amendment No. 10 Effective Date and (iv) commencing on
the Amendment No. 10 Effective Date, the Company shall be obligated to comply
with the requirements of the Sections 5.08, 5.09, 5.10 and 5.17 of the Credit
Agreement (as amended hereby) which relate to periods on or after the Amendment
No. 10 Effective Date and failure by the Company to do so shall entitle the
Agents and the Banks to exercise rights and remedies under the Financing
Documents in accordance with their terms.

       SECTION 4. Representations and Warranties. (a) Section 4.06(c) of the
Credit Agreement is amended by replacing the date "September 30, 1998" contained
therein with the date "March 31, 2000".

       (b) Section 4.07 of the Credit Agreement is amended by inserting after
the words "by the Company to the Banks" the words "or disclosed in the Company's
annual report on form 10-K for the 1999 fiscal year as filed with the Securities
and Exchange Commission prior to the Amendment No. 10 Effective Date".

       (c) The Company represents and warrants that:

              (i) The consolidated balance sheets of the Company and its
       Consolidated Subsidiaries as of December 31, 1999, December 31,1998, and
       December 31, 1997, respectively, and the related consolidated statements
       of operations and cash flows for each such fiscal year, delivered

                                       14
<PAGE>   15

       to the Banks prior to the Amendment No. 10 Effective Date pursuant to
       Section 5.22 of the Credit Agreement, fairly present in all material
       respects, in conformity with generally accepted accounting principles,
       the consolidated financial position of the Company and its Consolidated
       Subsidiaries as of the respective dates thereof, and their consolidated
       results of operations and cash flows for such fiscal years.

              (ii) The consolidated balance sheet of the Company and its
       Consolidated Subsidiaries as of March 31, 2000 and the related
       consolidated statements of operations and cash flows for the three months
       then ended, together with the consolidating balance sheet, statement of
       operations and operating cash flows for such quarter for each of the
       Company's Consolidated Subsidiaries delivered to the Banks prior to the
       Amendment No. 10 Effective Date fairly present in all material respects,
       in conformity with generally accepted accounting principles applied on a
       basis consistent with the financial statements referred to in subsection
       (i), the consolidated financial position of the Company and its
       Consolidated Subsidiaries, as of such date, and their consolidated
       results of operations and cash flows for such three month period (subject
       to normal year-end adjustments).

              (iii) The projections delivered by the Company to the Banks prior
       to the Amendment No. 10 Effective Date in accordance with Section 5.22 of
       the Credit Agreement (including the projected balance sheet of the
       Company and its Consolidated Subsidiaries as of December 31, 2000 and
       related projected statement of operations and cash flows for such fiscal
       year) have been prepared by the Company in good faith based on
       assumptions believed to be reasonable at the time.

              (iv) Since March 31, 2000 there has been no material adverse
       change in the business, financial position or results of operations of
       the Company and its Consolidated Subsidiaries, taken as a whole, and no
       event has taken place which is reasonably likely to have such a material
       adverse effect in the future.

              (v) The Company intends to consummate the MDA Share Sale (or to
       cause New MDH to consummate) a sale of shares of common stock of MDA
       pursuant to a registered offering substantially on the terms described by
       the Company to the Banks prior to the Amendment No. 10 Effective Date)
       for cash proceeds in the amount currently estimated to be not less than
       $22,000,000, subject to the rights of underwriters to reduce the number
       of shares of MDA to be sold pursuant thereto.

                                       15
<PAGE>   16

       SECTION 5. Restatement Date. The Banks and the Company acknowledge and
agree that this Amendment No. 10 shall constitute the restatement of the Credit
Agreement contemplated by Section 5.23 of the Credit Agreement and the
Restatement Date referred to in Section 2.10(e) of the Credit Agreement shall be
the Amendment No. 10 Effective Date.

       SECTION 6. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of New York.

       SECTION 7. Counterparts, Effectiveness. This Amendment may be signed in
any number of counterparts, each of which shall be an original, with the same
effect as if the signatures thereto and hereto were upon the same instrument.
This Amendment shall become effective on the date (the "AMENDMENT NO. 10
EFFECTIVE DATE") on which the Administrative Agent shall have received:

              (i) duly executed counterparts hereof signed by the Company and
       the Required Banks (or, in the case of any party as to which an executed
       counterpart shall not have been received, the Administrative Agent shall
       have received telegraphic, telex or other written confirmation from such
       party of execution of a counterpart hereof by such party); and

              (ii) payment in full of all the fees payable by the Company
       pursuant to Section 2.17 of the Credit Agreement, for the account of each
       of the Banks entitled to such fees pursuant to the terms of such Section.

                                       16
<PAGE>   17

       IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the date first above written.

ORBITAL SCIENCES CORPORATION

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

MORGAN GUARANTY TRUST COMPANY OF NEW YORK

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

THE BANK OF NOVA SCOTIA

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

BANK OF AMERICA, N.A., f/k/a
  NATIONSBANK, N.A.

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

                                       17
<PAGE>   18

FIRST UNION COMMERCIAL CORPORATION

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

DEUTSCHE BANK AG, NEW YORK
AND/OR CAYMAN ISLAND BRANCHES

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

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

KEYBANK NATIONAL ASSOCIATION

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

BANK OF TOKYO-MITSUBISHI TRUST COMPANY

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

                                       18
<PAGE>   19

WACHOVIA BANK, N.A.

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

CHEVY CHASE BANK

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

MORGAN GUARANTY TRUST COMPANY
  OF NEW YORK, as Administrative Agent and as
  Collateral Agent

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

Acknowledged by:

ENGINEERING TECHNOLOGIES, INC.

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

ORBITAL SPACE SYSTEMS, INC.

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

                                       19
<PAGE>   20

ORBITAL COMMERCIAL SYSTEMS, INC.

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

ORBITAL INTERNATIONAL, INC.

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

ORBITAL SERVICES CORPORATION

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

ORBITAL NAVIGATION CORPORATION

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

ORBLINK LLC

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

                                       20<PAGE>   1

                                                                    Exhibit 10.3

                               AMENDMENT NO. 11
                                      TO
                          THIRD AMENDED AND RESTATED
                      CREDIT AND REIMBURSEMENT AGREEMENT

       AMENDMENT No. 11 dated as of July 31, 2000 among ORBITAL SCIENCES
CORPORATION (the "COMPANY"), the BANKS listed on the signature pages hereof and
MORGAN GUARANTY TRUST COMPANY OF NEW YORK, as Administrative Agent (the
"ADMINISTRATIVE AGENT") and as Collateral Agent (the "COLLATERAL AGENT").

                                   WITNESSETH:

       WHEREAS, the parties hereto have heretofore entered into a Third Amended
and Restated Credit and Reimbursement Agreement dated as of December 21, 1998
(as amended from time to time, the "CREDIT AGREEMENT"); and

       WHEREAS, the Company and the Banks wish to amend the Credit Agreement as
set forth herein;

       NOW, THEREFORE, the parties hereto agree as follows:

       SECTION 1. Definition; References. Unless otherwise specifically defined
herein, each term used herein that is defined in the Credit Agreement shall have
the meaning assigned to such term in the Credit Agreement. Each reference to
"hereof", "hereunder", "herein" and "hereby" and each other similar reference
and each reference to "this Agreement" and each other similar reference
contained in the Credit Agreement shall from and after the Amendment No. 11
Effective Date (as defined in Section 17 below) refer to the Credit Agreement as
amended hereby.

       SECTION 2. Amendments to the Definitions. (a) The definition of "Target
Amount" contained in Section 2.10(e) of the Credit Agreement is hereby deleted
in its entirety.

       (b) Section 1.01 of the Credit Agreement is amended by adding therein the
following definitions in alphabetical order:

<PAGE>   2

       "AMENDMENT NO. 11 EFFECTIVE DATE" means the date of effectiveness of
Amendment No.11 to this Agreement.

       "FAIRCHILD SALE" means the sale by the Company or any of its wholly-owned
domestic subsidiaries of all or any portion of the assets of the Fairchild
Defense Division pursuant to an asset purchase or other transaction structure
for the purpose of the disposition of such assets substantially on the terms
described by the Company to the Banks prior to the Amendment No. 11 Effective
Date.

       "FAIRCHILD SALE DATE" means the date of consummation of the Fairchild
Sale.

       "MAGELLAN SALE" means the sale by the Company or any of its wholly-owned
domestic subsidiaries of all or any portion of the capital stock or all or any
substantial part of the assets of Magellan (it being understood that any such
sale or disposition may or may not include the Navigation Sale), substantially
on the terms described by the Company to the Banks prior to the Amendment No. 11
Effective Date.

       "MAGELLAN SALE DATE" means the date of consummation of the Magellan Sale.

       "MAGELLAN STOCK CONSIDERATION" means any capital stock, limited liability
company interests, partnership interests or other equity interests of Trimble
Navigation Ltd. or any other Person received by the Company as consideration
with respect to the Magellan Sale.

       "NAVIGATION" means Orbital Navigation Corporation, a Delaware
corporation, and its successors.

       "NAVIGATION SALE" means the sale by the Company or any of its
wholly-owned domestic subsidiaries of all or substantially all of the capital
stock or all or substantially all of the assets of Navigation, substantially on
the terms described by the Company to the Banks prior to the Amendment No. 11
Effective Date.

       "NAVIGATION SALE DATE" means the date of consummation of the Navigation
Sale.

       "SUBJECT ASSET SALES" means (i) the Magellan Sale, (ii) the Navigation
Sale and (iii) the Fairchild Sale. Each Subject Asset Sale constitutes an "Asset
Sale" under this Agreement.

       (c) The following definitions set forth in Section 1.01 of the Credit
Agreement are amended to read in their entirety as follows:

                                       2
<PAGE>   3

       "CONSOLIDATED EBITDA" means, for any period, Consolidated Net Income for
such period plus, to the extent deducted in determining such Consolidated Net
Income, without duplication, the aggregate amount of (i) consolidated interest
expense, (ii) income tax expense, (iii) depreciation, amortization and other
similar non-cash charges, (iv) one-time accounting charges resulting in
adjustments to earnings for each of the fiscal quarters of the fiscal year ended
December 31, 1998, up to an aggregate amount equal to $35,600,000, (v)
write-offs with respect to the investment made by the Company in CCI
International N.V. for any fiscal quarter ended prior to December 31, 1999, up
to an aggregate amount equal to $21,400,000, (vi) solely for any period ended on
or prior to February 22, 2000, Excluded Charges, up to an aggregate amount equal
to $5,000,000 and (vii) solely for the fiscal quarter ended June 30, 2000,
non-cash charges with respect to the settlement of shareholder litigation in an
aggregate amount not to exceed $11,500,000.

       "EARNINGS AVAILABLE FOR FIXED CHARGES" means, for any period,
Consolidated Net Income for such period (excluding therefrom (i) any
extraordinary items of gain or loss, (ii) any gain or loss of any other Person
accounted for pursuant to the equity method, except in the case of gain to the
extent of cash distributions received from such Person during the relevant
period), plus the aggregate amounts deducted in determining Consolidated Net
Income for such period in respect of (i) interest and rental expense, (ii)
income taxes, (iii) write-offs with respect to the investment made by the
Company in CCI International N.V. for any fiscal quarter ended prior to December
31, 1999, up to an aggregate amount equal to $21,400,000, (iv) Excluded Charges,
up to an aggregate amount equal to $5,000,000, (v) one-time accounting charges
resulting in adjustments to earnings for each of the fiscal quarters of the
fiscal year ended December 31, 1998, up to an aggregate amount equal to
$35,600,000, (vi) non-cash asset impairment charges incurred on or prior to
December 31, 1999 up to an aggregate amount equal to $17,027,000, non-cash
write-downs up to an aggregate amount equal to $14,820,000 incurred on or prior
to December 31, 1999 and other non-cash charges similar to depreciation and
amortization (but not including depreciation or amortization) and (vii) solely
for the fiscal quarter ended June 30, 2000, non-cash charges with respect to the
settlement of shareholder litigation in an aggregate amount not to exceed
$11,500,000.

       SECTION 3. Deletion of Certain Caps on Commitment Reductions as a Result
of Reduction Events. (a) Section 2.10(d) of the Credit Agreement is hereby
amended by:

              (i) deleting the comma at the end of clause (i) and replacing it
with the word "and";

              (ii) deleting clauses (ii) and (iii) in their entirety;

                                       3
<PAGE>   4

              (iii) renumbering clause (iv) as clause (ii) and amending it to
       read in its entirety as follows:

              (ii) in no event shall the Commitments be reduced below
$70,000,000 pursuant to this subsection (d), unless such reduction is effected
as a result of a Reduction Event constituting a Subject Asset Sale.

       (b) Section 2.10(f)(iii) of the Credit Agreement is hereby amended to
read in its entirety as follows:

       (iii) If the Magellan Sale Date has occurred on or prior to December 31,
2000 and 55% of the Net Cash Proceeds therefrom is less than $15,000,000 then on
December 31, 2000 the Commitments shall be automatically and ratably reduced by
an aggregate amount equal to $14,250,000 (in addition to any reduction of the
Commitments that may be effected on such date pursuant to subsections (d) or (e)
above). If the Cooler Acquisition Date has occurred and the Additional Debt Date
has not occurred on or prior to the Cooler Acquisition Date, then in no event
shall the Commitments be reduced pursuant to Section 2.10(d) below $60,000,000,
unless such reduction is effected as a result of a Reduction Event constituting
a Subject Asset Sale.

       SECTION 4. Postponement of August 1, 2000 Scheduled Commitment Reduction
to December 31, 2000. (a) Section 2.10(e) of the Credit Agreement is hereby
amended by replacing the table contained therein with the following table:

<TABLE>
<CAPTION>
           -------------------------------------------------------------------------------
                    DATE                                       AGGREGATE AMOUNT
           -------------------------------------------------------------------------------
           <S>                                          <C>
                    December 31, 2000                          $125,000,000
           -------------------------------------------------------------------------------
                    July 1, 2001                               $85,000,000
           -------------------------------------------------------------------------------
</TABLE>

       (b) Section 2.10(f)(ii) of the Credit Agreement is hereby amended by
replacing the table contained therein with the following table:

<TABLE>
<CAPTION>
           -------------------------------------------------------------------------------
                    DATE                                       AGGREGATE AMOUNT
           -------------------------------------------------------------------------------
           <S>                                          <C>
                    December 31, 2000                          $115,000,000
           -------------------------------------------------------------------------------
                    July 1, 2001                               $75,000,000
           -------------------------------------------------------------------------------
</TABLE>

       SECTION 5. Certain Other Prepayments of Loans. Section 2.10(h) of the
Credit Agreement is hereby amended to read in its entirety as follows:

                                       4
<PAGE>   5

       If the Cooler Acquisition Date has occurred and the Additional Debt Date
has not occurred on or prior to the Cooler Acquisition Date, then on the Cooler
Acquisition Date, in addition to any prepayment of the Loans to be made by the
Borrowers pursuant to any other subsection of this Section 2.10, the Borrowers
shall prepay, together with accrued interest thereon, Loans in an aggregate
principal amount equal to $10,000,000. If the Magellan Sale Date has occurred on
or prior to December 31, 2000 and 55% of the Net Cash Proceeds therefrom is less
than $15,000,000, in addition to any prepayment of the Loans pursuant to any
other subsection of this Section 2.10, the Borrowers shall prepay, on December
31, 2000, together with accrued interest thereon, Loans in the aggregate
principal amount equal to $750,000. On any date after the Amendment No. 11
Effective Date on which any Reduction Event is consummated, in addition to any
prepayment of the Loans to be made by the Borrowers pursuant to any other
subsection of this Section 2.10 (and, if such Reduction Event is the Magellan
Sale, pursuant to the immediately preceding sentence), the Borrowers shall
prepay, together with accrued interest thereon, Loans in an aggregate principal
amount equal to 5% of the Net Cash Proceeds of such Reduction Event. Any
prepayment of the Loans made pursuant to this subsection (h) shall not cause any
reduction of the Commitments.

       SECTION 6. Limitation on New Extensions of Credit. (a) Sections 2.02(e)
and (f) to the Credit Agreement are amended to read in their entirety as
follows:

       (e) The Company agrees that, except as permitted in subsection (f) below,
on and after the Amendment No. 11 Effective Date, neither the Company nor any
other Borrower shall deliver a Notice of Borrowing or a request for issuance of
a Letter of Credit or otherwise request any Bank (including the LC Bank) to
extend any credit to the Company or any other Borrower under the facilities
created pursuant to the Credit Agreement, and that, notwithstanding any other
provision hereof, on and after the Amendment No.11 Effective Date, no Bank
(including the LC Bank) shall be required to make any Loan, or issue or
participate in any Letter of Credit (it being understood that nothing in this
sentence shall be construed to prohibit the Company from delivering a Notice of
Interest Rate Election with respect to any Loan outstanding prior to the
Amendment No. 6 Effective Date or any Loan made on or after the Cooler
Acquisition Date and permitted to be made pursuant to subsection (f) below and
continuing or converting any such Loan on the terms set forth in such Notice of
Interest Rate Election).

       (f) (i) In addition to the rights set forth in clauses (ii) and (iii) of
this subsection (f), if the Cooler Acquisition Date has occurred and the
Additional Debt Date has not occurred on or prior to the Cooler Acquisition Date
and the Borrowers shall have complied with their obligations under Section
2.10(h), the Company or any other Borrower may deliver a Notice of Borrowing or
request for issuance of a Letter of Credit, on any date (a "test date") on or
after the Cooler

                                       5
<PAGE>   6

Acquisition Date, and the Banks (including the LC Bank) shall be required to
make such requested Loan, or issue or participate in such requested Letter of
Credit (subject to satisfaction of the conditions set forth in Section 3.03 and,
if applicable, Section 3.04); provided that after giving effect to any such Loan
or issuance of or participation in any such Letter of Credit, the portion of the
total Exposure of all the Banks that has been incurred on or after the Cooler
Acquisition Date in reliance on this clause (i) and that is outstanding on such
test date shall not exceed $10,000,000 (it being understood that nothing in this
sentence shall be construed to prohibit the Company from delivering a Notice of
Interest Rate Election with respect to any Loan outstanding prior to the
Amendment No. 6 Effective Date or any Loan permitted to be made pursuant to this
subsection (f) and continuing or converting any such Loan on the terms set forth
in such Notice of Interest Rate Election).

       (ii) In addition to the rights set forth in clauses (i) and (iii) of this
subsection (f), if any Reduction Event is consummated after the Amendment No. 11
Effective Date (the date of consummation of any such Reduction Event, a
"REDUCTION DATE") and as a result of such Reduction Event (x) the Commitments
have been mandatorily reduced pursuant to Section 2.10 by an amount equal to 50%
of the Net Cash Proceeds thereof and (y) the Borrowers shall have complied in
full with their obligations to repay the Loans under Section 2.10 (including
without limitation Section 2.10(h)), the Company or any other Borrower may
deliver a Notice of Borrowing or request for issuance of a Letter of Credit, on
any date (a "test date") on or after the Reduction Date with respect to such
Reduction Event, and the Banks (including the LC Bank) shall be required to make
such requested Loan, or issue or participate in such requested Letter of Credit
(subject to satisfaction of the conditions set forth in Section 3.03 and, if
applicable, Section 3.04); provided that after giving effect to any such Loan or
issuance of or participation in any such Letter of Credit, the portion of the
total Exposure of all the Banks that has been incurred on or after such
Reduction Date in reliance on this clause (ii) and that is outstanding on such
test date shall not exceed 5% of the Net Cash Proceeds with respect to such
Reduction Event and all other Reduction Events that have been consummated after
the Amendment No. 11 Effective Date and on or prior to such Reduction Date (it
being understood that nothing in this sentence shall be construed to prohibit
the Company from delivering a Notice of Interest Rate Election with respect to
any Loan outstanding prior to the Amendment No. 6 Effective Date or any Loan
permitted to be made pursuant to this subsection (f) and continuing or
converting any such Loan on the terms set forth in such Notice of Interest Rate
Election);

       (iii) In addition to the rights set forth in clauses (i) and (ii) of this
subsection (f), if the Magellan Sale is consummated on or prior to December 31,
2000 and the Borrowers shall have complied with their obligations under Section
2.10, the Company or any other Borrower may deliver a Notice of Borrowing or

                                       6
<PAGE>   7

request for issuance of a Letter of Credit, on any date (a "test date") on or
prior to December 31, 2000, and the Banks (including the LC Bank) shall be
required to make such requested Loan, or issue or participate in such requested
Letter of Credit (subject to satisfaction of the conditions set forth in Section
3.03 and, if applicable, Section 3.04); provided that after giving effect to any
such Loan or issuance of or participation in any such Letter of Credit, the
portion of the total Exposure of all the Banks that has been incurred on or
prior to December 31, 2000 in reliance on this clause (iii) and that is
outstanding on such date shall not exceed $750,000 (it being understood that
nothing in this sentence shall be construed to prohibit the Company from
delivering a Notice of Interest Rate Election with respect to any Loan
outstanding prior to the Amendment No. 6 Effective Date or any Loan permitted to
be made pursuant to this subsection (f) and continuing or converting any such
Loan on the terms set forth in such Notice of Interest Rate Election).

       (b) Section 3.03(e) of the Credit Agreement is amended to read in its
entirety as follows:

       (e) if such Credit Event occurs after the Amendment No. 11 Effective
Date, after giving effect to such Credit Event (and the application of the
proceeds thereof), the portion of the total Exposure of all the Banks that has
been incurred on or after the Amendment No. 11 Effective Date and that is
outstanding on such date does not exceed the aggregate amount of total Exposure
permitted to be incurred after the Amendment No. 11 Effective Date in accordance
with clauses (i), (ii) and (iii) of Section 2.02(f).

       SECTION 7. Change in a Condition Precedent with Respect to the Cooler
Acquisition. Clause (i)(B)(y) of Section 5.07(p) of the Credit Agreement is
hereby amended by to read in its entirety as follows: "(y) [intentionally
deleted]".

       SECTION 8. Waiver of One Condition with Respect to the Consummation of
the Cooler Acquisition. (a) With respect to the consummation by the Company of
the Cooler Acquisition, the Banks hereby (i) waive the requirement set forth in
clause (i)(A)(x) of Section 5.07(p) of the Credit Agreement that the Asset Sales
(other than the MDA Share Sale) that have generated the amount of Net Cash
Proceeds required pursuant to such clause not reduce Consolidated EBITDA by more
than the expected increase in Consolidated EBITDA resulting from the Cooler
Acquisition (it being understood that the Banks do not waive the requirement
that the Company and its wholly-owned domestic subsidiaries shall have generated
cash proceeds of not less than $140,000,000 or any other condition set forth in
Section 5.07(p)) and (ii) waive any Default or Event of Default arising under
Section 6.01(c) of the Credit Agreement by reason of noncompliance with such
requirement.

                                       7
<PAGE>   8

       (b) The waivers set forth in subsection (a) of this Section 8 (i) shall
apply only if the Asset Sales causing the reduction in Consolidated EBITDA are
Subject Asset Sales (as defined in the Credit Agreement as amended by this
Amendment) and (ii) shall cease to be in effect on the Cooler Acquisition Date
unless the Borrowers shall have complied with their obligations under Sections
2.10(g) and 2.10(h) of the Credit Agreement on the Cooler Acquisition Date.

       (c) Except as provided in subsection (a) above, this Section 8 shall not
operate as a waiver of any right, remedy, power or privilege of the Banks under
any Financing Document or of any other term or condition of any Financing
Document.

       SECTION 9. Temporary Waiver of Noncompliance with Certain Covenants as a
Result of Subject Asset Sales. (a) With respect to the consummation by the
Company or any of its domestic wholly-owned Subsidiaries of any Subject Asset
Sale, the Banks hereby (i) waive compliance by the Company with the provisions
of Sections 5.08, 5.09 and 5.10 of the Credit Agreement solely as a result of a
reduction in Consolidated Net Worth, Consolidated EBITDA or Earnings Available
for Fixed Charges due to the consummation of a Subject Asset Sale and (ii) waive
any Default or Event of Default arising under Section 6.01(c) of the Credit
Agreement by reason of such noncompliance.

       (b) With respect to any Subject Asset Sale, the waivers granted in
subsection (a) of this Section 9 (i) shall expire on the 30th calendar day after
consummation of such Subject Asset Sale and (ii) shall be effective if, and only
if, (x) at least 5 Domestic Business Days prior to the consummation of such
Subject Asset Sale, the Company shall have delivered to the Banks a certificate
(each, a "SUBJECT ASSET SALE CERTIFICATE") of the chief financial officer or the
treasurer of the Company describing such Subject Asset Sale, the material terms
thereof, the proposed date of consummation thereof and setting forth the
calculations (on a pro forma basis, giving effect to such Subject Asset Sale)
required to demonstrate whether, after giving effect to such Subject Asset Sale,
the Company shall be in compliance with the provisions of Sections 5.08, 5.09
and 5.10 of the Credit Agreement and (y) on the date of consummation of such
Subject Asset Sale, the Borrowers shall have complied with their obligations
under Section 2.10(g) of the Credit Agreement.

       (c) If the covenant calculations set forth in any Subject Asset Sale
Certificate delivered by the Company to the Banks with respect to any Subject
Asset Sale shall demonstrate that the Company, after giving effect to such
Subject Asset Sale, shall not be in compliance with the provisions of Sections
5.08, 5.09 and 5.10 of the Credit Agreement solely as a result of a reduction in
Consolidated Net Worth, Consolidated EBITDA or Earnings Available for Fixed
Charges, the Banks and the Company agree that they shall use their respective
best efforts to

                                       8
<PAGE>   9

enter into an amendment to the Credit Agreement on or prior to the 30th calendar
day after consummation of such Subject Asset Sale to determine new covenant
levels applicable under Sections 5.08, 5.09 and 5.10 of the Credit Agreement
consistent with the methodology and intent used in deriving the covenant levels
established in Amendment No. 10 to the Credit Agreement after giving effect to
such Subject Asset Sale.

       (d) The Company and the Banks agree that any Magellan Stock
Consideration, as defined in the Credit Agreement as amended hereby, shall not
constitute an "Investment" for purposes of Section 5.07.

       (e) Except as provided in subsections (a) and (d) above, this Section 9
shall not operate as a waiver of any right, remedy, power or privilege of the
Banks under any Financing Document or of any other term or condition of any
Financing Document (including without limitation as a waiver of noncompliance by
the Company with any other term or condition of any Financing Document as a
result of any Subject Asset Sale).

       SECTION 10. Release of Guaranty and Collateral in Connection with the
Navigation Sale and the Fairchild Sale. (a) The Banks agree that, effective on
the date of the Navigation Sale (as defined in the Credit Agreement as amended
hereby):

       (i) if the Navigation Sale is a sale of all or substantially all of the
capital stock of Navigation, (x) the Lien on such capital stock created under
the Pledge Agreement (including all proceeds thereof other than proceeds thereof
which must be paid to the Banks pursuant to Section 2.10 of the Credit
Agreement) shall be released and (y) Navigation shall be released from its
obligations as a Guarantor under the Credit Agreement, in each case concurrently
with the consummation of such Navigation Sale and compliance by the Borrowers
with their obligations under Section 2.10 of the Credit Agreement, and

       (ii) if the Navigation Sale occurs, the Lien on all assets held by
Navigation created under the Subsidiary Security Agreement (including all
proceeds thereof other than proceeds thereof which must be paid to the Banks
pursuant to Section 2.10 of the Credit Agreement) shall be released concurrently
with the consummation of such Navigation Sale and compliance by the Borrowers
with their obligations under Section 2.10 of the Credit Agreement.

       (b) The Banks agree that, effective on the date of the Fairchild Sale (as
defined in the Credit Agreement as amended hereby), if the Fairchild Sale
occurs, (i) the Lien on the assets of the Fairchild Defense Division created
under the Subsidiary Security Agreement (including all proceeds thereof other
than proceeds thereof which must be paid to the Banks pursuant to Section 2.10
of the Credit Agreement) shall be released concurrently with the consummation of
such

                                       9
<PAGE>   10

Fairchild Sale and compliance by the Borrowers with their obligations under
Section 2.10 of the Credit Agreement and (ii) the Company and each other
Subsidiary Pledgor (as defined in the Pledge Agreement) shall be released from
(A) its obligations under Section 3(b) of the Pledge Agreement with respect to
the pledge to the Collateral Agent of the stock, limited liability company
interests, partnership interests or other equity interests of a new direct
Subsidiary formed solely for the purpose of consummating the Fairchild Sale
through a stock purchase of the capital stock of such Subsidiary, and (B) with
respect to Section 5.19(b) of the Credit Agreement, its obligations with respect
to causing such Subsidiary to become a "Guarantor" under the Credit Agreement;
provided that (A) in no event shall any assets be transferred to such Subsidiary
(i) which are not assets of the Fairchild Defense Division or (ii) prior to the
execution of definitive agreements by all parties to the Fairchild Sale and such
Subsidiary shall incur no liabilities other than liabilities in connection with
the Fairchild Sale and (B) the releases granted pursuant to this subsection (b)
shall be effective only so long as such Subsidiary shall not be required to be a
guarantor with respect to the NML Debt.

       (c) The Banks agree that, effective on the date of the Magellan Sale (as
defined in the Credit Agreement as amended hereby), the Lien created under the
Security Agreement on the Magellan Note (as defined therein), shall be released,
concurrently with (x) the consummation of the Magellan Sale and compliance by
the Company and each other Subsidiary Pledgor under the Pledge Agreement with
the provisions of Section 3(b) of the Pledge Agreement with respect to any
Magellan Stock Consideration received by the Company or any of its subsidiaries
in connection with the Magellan Sale and (y) compliance by the Borrowers with
their obligations under Section 2.10 of the Credit Agreement, and the Collateral
Agent shall return the Magellan Note to the Company.

       (d) The Company agrees that any Magellan Stock Consideration shall be
issued to the Company or a Subsidiary Pledgor, until disposed of pursuant to a
sale or other disposition (including, without limitation, in connection with the
execution of a forward purchase contract with respect to such Magellan Stock
Consideration) for cash proceeds or until the Company incurs Debt pursuant to a
Debt Issuance as contemplated by the last sentence of Section 5.14 of the Credit
Agreement as amended hereby (any such transaction, a "MAGELLAN STOCK
MONETIZATION"). The Banks and the Company acknowledge and agree that any cash
received upon any Magellan Stock Monetization constitutes Net Cash Proceeds with
respect to the Magellan Sale and shall be subject to the provisions of Section
2.10. The Banks further agree that upon the consummation of any Magellan Stock
Monetization and receipt by the Company or any Subsidiary Pledgor of cash
proceeds with respect thereto, the Lien created under the

                                       10
<PAGE>   11

Subsidiary Security Agreement on the Magellan Stock Consideration subject to
such Magellan Stock Monetization shall be released, concurrently with compliance
by the Borrowers with their obligations under Section 2.10 of the Credit
Agreement. Failure by the Company to comply with the provisions set forth in
this subsection shall constitute an Event of Default and entitle the Banks and
the Agents to exercise all rights and remedies available under the Financing
Documents upon the occurrence of an Event of Default.

       (e) The Banks hereby authorize the Collateral Agent to execute any
release instruments to evidence the release of any Lien effected pursuant to
subsections (a), (b), (c) and (d) of this Section 10.

       SECTION 11. Additional Covenants with Respect to Subject Asset Sales.
Section 5.01 of the Credit Agreement is amended by (i) deleting the "and" at the
end of clause (j) thereof, (ii) renumbering clause (k) thereof as clause (1) and
inserting a new clause (k) immediately after clause (j) thereof to read in its
entirety as follows:

       (k) (i) On or before the Amendment No. 11 Effective Date, the Company
will deliver to the Administrative Agent a schedule of proposed Subject Asset
Sales for the period from the Amendment No. 11 Effective Date to the Termination
Date setting forth the then contemplated material terms of each such Asset Sale
and the then contemplated proposed timetable with respect thereto, including the
proposed date of consummation thereof and (ii) on the 22nd day of each calendar
month (beginning with September 22, 2000), the Company will deliver to the
Administrative Agent a written report updating the most recent information
delivered by the Company pursuant to this clause or clause (i) of this
subsection, as the case may be.

       SECTION 12. Limitations on Type of Consideration Received in Asset Sales.
The following sentence is added at the end of Section 5.15 of the Credit
Agreement:

       Neither the Company nor any Subsidiary will make any Asset Sale (or, in
the case of any Subsidiary other than a domestic wholly-owned subsidiary, any
disposition of assets that would constitute an "Asset Sale" if made by the
Company) unless the consideration therefor (x) is determined pursuant to an
arm's-length transaction and (y) shall consist solely of cash payable at closing
(or assets that will be converted into cash, and are so converted, concurrently
with the consummation thereof), or, in the case of the Magellan Sale, converted
into cash as soon as possible.

       SECTION 13. Additional Negative Pledge Restriction. Section 5.14 of the
Credit Agreement is amended by adding the following sentence at the end thereof:

                                       11
<PAGE>   12

       Notwithstanding any provision contained in this Section 5.14, neither the
Company nor any Subsidiary will create, assume or suffer to exist any Lien on
any Magellan Stock Consideration, other than Liens which secure Debt (i) that
constitutes a Debt Issuance, so long as the Borrowers shall have applied the Net
Cash Proceeds thereof in accordance with Section 2.10 and (ii) that is
non-recourse to any assets of the Company or any of its Subsidiaries other than
such Magellan Stock Consideration.

       SECTION 14. Additional Fees. The following sentences are added at the end
of Section 2.17 of the Credit Agreement:

              On October 31, 2000, if the Commitments on such date are not less
              than $125,000,000, the Company shall pay to the Administrative
              Agent for the account of each Bank a fee in an amount equal to
              12.5 basis points on such Bank's Commitment as in effect on such
              date. On December 31, 2000, if the Commitments on such date are
              not less than $90,000,000, the Company shall pay to the
              Administrative Agent for the account of each Bank a fee in an
              amount equal to 12.5 basis points on such Bank's Commitment as in
              effect on such date.

       SECTION 15. Representations and Warranties. The Company represents and
warrants that, except for developments relating to ORBCOMM Global as previously
disclosed to the Banks, the representations and warranties set forth in Sections
4.06(c) and 4.12 of the Credit Agreement are true and correct on and as of the
Amendment No. 11 Effective Date except that, in the case of Section 4.12, such
representation and warranty shall not apply to the original financial statements
for the fiscal years ended December 31, 1997, 1998 and 1999 delivered by the
Company to the Banks pursuant to the Credit Agreement (but with respect to
financial statements for such fiscal years, shall apply to the restated
financial statements for such fiscal years delivered by the Company to the Banks
on or about April, 2000).

       SECTION 16. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of New York.

       SECTION 17. Counterparts, Effectiveness. This Amendment may be signed in
any number of counterparts, each of which shall be an original, with the same
effect as if the signatures thereto and hereto were upon the same instrument.
This Amendment shall become effective on the date (the "AMENDMENT NO. 11
EFFECTIVE DATE") on which the Administrative Agent shall have received:

              (i) duly executed counterparts hereof signed by the Company and
       all the Banks (or, in the case of any party as to which an executed
       counterpart shall not have been received, the Administrative Agent shall

                                       12
<PAGE>   13

       have received telegraphic, telex or other written confirmation from such
       party of execution of a counterpart hereof by such party);

              (ii) for the account of each Bank, an amendment fee in an amount
       equal to 20 basis points of the amount of such Bank's Commitment as in
       effect on such date; and

              (iii) payment in full of all expenses payable by the Company
       pursuant to Section 10.03 of the Credit Agreement with respect to which
       the Company shall have received invoices prior to July 25, 2000.

                                       13
<PAGE>   14

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the date first above written.

                                    ORBITAL SCIENCES CORPORATION

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

                                    MORGAN GUARANTY TRUST COMPANY
                                      OF NEW YORK

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

                                    THE BANK OF NOVA SCOTIA

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

                                    BANK OF AMERICA, N.A., f/k/a
                                      NATIONSBANK, N.A.

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

<PAGE>   15

                                    FIRST UNION COMMERCIAL CORPORATION

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

                                    DEUTSCHE BANK AG, NEW YORK
                                      AND/OR CAYMAN ISLAND BRANCHES

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

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

                                    KEYBANK NATIONAL ASSOCIATION

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

                                    BANK OF TOKYO-MITSUBISHI TRUST COMPANY

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

<PAGE>   16

                                    WACHOVIA BANK, N.A.

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

                                    CHEVY CHASE BANK

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

                                    MORGAN GUARANTY TRUST COMPANY
                                      OF NEW YORK, as Administrative Agent and
                                      as Collateral Agent

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

Acknowledged by:

ENGINEERING TECHNOLOGIES, INC.

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

ORBITAL SPACE SYSTEMS, INC.

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

<PAGE>   17

ORBITAL COMMERCIAL SYSTEMS, INC.

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

ORBITAL INTERNATIONAL, INC.

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

ORBITAL SERVICES CORPORATION

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

ORBITAL NAVIGATION CORPORATION

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

ORBLINK LLC

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

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