Document:

<PAGE>   1
                                                                    EXHIBIT 10.8

                   AMENDMENT NO. 1 TO THE AMENDED AND RESTATED
                         CAPITAL SUBSCRIPTION AGREEMENT

     AMENDMENT NO. 1 dated as of June 20, 2000, made by and among (i) NEXTEL
ARGENTINA S.R.L. (the "Borrower"), a sociedad de responsabilidad limitada
organized under the laws of Argentina, (ii) NEXTEL INTERNATIONAL (ARGENTINA),
LTD. (the "Parent"), a company incorporated under the laws of the Cayman
Islands, and (iii) NEXTEL INTERNATIONAL, INC. (the "Parent Shareholder"), a
corporation organized under the laws of the State of Washington, United States
of America.

     The Borrower, the Parent and the Parent Shareholder are parties to a
Capital Subscription Agreement dated as of March 17, 1998 (as amended and
restated by the Amended and Restated Capital Subscription Agreement dated as of
May 12, 1999 and as further modified, supplemented and in effect from time to
time, the "Capital Subscription Agreement") and wish to amend certain provisions
of the Capital Subscription Agreement.

     Accordingly, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

     SECTION 1. Amendments.

     1.01. Definitions. The definition of "Equity Contribution" in Section 1 of
the Capital Subscription Agreement is hereby amended to read in its entirety as
follows:

          "Equity Contribution" means, as to any Person (i) the amount of cash
     consideration paid to such Person in exchange for newly-issued Capital
     Stock of such Person, (ii) the amount of any contribution of cash to such
     Person in respect of its Capital Stock made by any then-existing
     equityholder, (iii) in the case of the Borrower, the value of equipment
     contributed to the Parent by the Parent Shareholder, and to the Borrower by
     the Parent, in respect of its capital stock, so long as such equipment is
     newly manufactured and has been purchased by the Parent Shareholder from
     third party vendor(s), not an Affiliate, within 30 days prior to the date
     of delivery of such equipment to the Borrower and (iv) the value of
     payments made by the Parent Shareholder to third party vendors in respect
     of software, software design and software licensing utilized by the
     Borrower and its Subsidiaries and set forth in a certification to such
     effect delivered to the Administrative Agent and signed jointly by an
     officer of the Parent Shareholder and the Borrower, provided that the
     aggregate amount of such payments during any single fiscal year that may be
     treated as Equity Contributions shall not exceed U.S. $3,000,000. For
     purposes hereof, the value of any equipment contributed to the Parent and
     the Borrower as contemplated by the foregoing clause (iii) shall be valued
     at the purchase price therefor reflected on the invoice of the respective
     vendor, and the value of any software, software design and software
     licensing referred to in the foregoing clause

                Amendment No. 1 to Capital Subscription Agreement

<PAGE>   2
          (iv) shall be the amount thereof determined in good faith as being
     properly allocable to the Borrower and its Subsidiaries as set forth in the
     officers' certificate referred to in said clause (iv).

     1.02. New Equity Contributions. Section 2(c) of the Capital Subscription
Agreement is hereby amended to read in its entirety as follows:

          "(c) New Equity Contributions. The Parent Equity Holders shall make
     additional Equity Contributions to the Parent, by remitting the same in
     U.S. Dollars and in immediately available funds to the Equity Contribution
     Account or, alternatively, by contributing equipment as permitted by clause
     (iii) of the definition of "Equity Contribution" in Section 1 (all such
     additional Equity Contributions to the Parent being herein referred to as
     the "New Equity Contributions"), from time to time as herein provided, to
     the extent necessary so that the aggregate amount of (x) the Pre-Closing
     Equity Contributions, plus (y) the New Equity Contributions, so made in the
     Parent on or before the dates set forth below shall each be equal to or
     greater than the respective amounts set forth below beside such dates (as
     such amounts shall be adjusted in accordance with the proviso set forth
     below):

<TABLE>
<CAPTION>
                    Date                                       Amount
                    ----                                       ------
          <S>                                             <C>
          Amendment No. 3 Effective Date                  U.S.$ 65,500,000

          December 31, 1999                               U.S.$ 83,500,000

          March 31, 2000                                  U.S.$ 90,500,000

          June 30, 2000                                   U.S.$135,000,000

          September 30, 2000                              U.S.$180,000,000

          December 31, 2000                               U.S.$218,000,000

          March 31, 2001                                  U.S.$242,000,000

          June 30, 2001                                   U.S.$275,000,000

          September 30, 2001                              U.S.$306,000,000

          December 31, 2001                               U.S.$328,000,000

          March 31, 2002                                  U.S.$346,000,000

          June 30, 2002                                   U.S.$362,000,000

          September 30, 2002                              U.S.$406,000,000
</TABLE>

                Amendment No. 1 to Capital Subscription Agreement

                                      -2-
<PAGE>   3

<TABLE>
<CAPTION>
                    Date                                       Amount
                    ----                                       ------
          <S>                                             <C>
          December 31, 2002                               U.S.$445,000,000
</TABLE>

     provided that the amount set forth above for any date shall be reduced or
     increased by the amounts set forth below in the event any of the following
     conditions shall be met (reductions and increases in the following clauses
     (i) and (ii) each to be independent of the other):

               (i) in the event that the Borrower shall elect to reduce the
          cumulative permitted amount of Capital Expenditures through any
          December 31 as contemplated by clause (i) of Section 7.08(c) of the
          Credit Agreement by sending a "Notice of Capital Expenditure
          Reduction" to the Administrative Agent and the Lenders as provided
          therein, then the amount of required New Equity Contributions as at
          said December 31 and each date set forth in the schedule above after
          such December 31 shall be reduced by an equivalent amount; and

               (ii) in the event that the cumulative amount of EBITDA for the
          period (treated for these purposes as a single accounting period)
          commencing on January 1, 2000 through and including the fiscal quarter
          ending on any date set forth in the schedule below shall (x) be
          greater than the projected EBITDA for such period set forth in the
          schedule below, then the amount of required New Equity Contributions
          as at said date and each date set forth in the schedule above after
          such date shall be reduced by an equivalent amount and (y) be less
          than the projected EBITDA for such period set forth in the schedule
          below, then the amount of required New Equity Contributions as at said
          date and each date set forth in the schedule above after such date
          shall be increased by an equivalent amount:

<TABLE>
<CAPTION>
                 Period Ending                                Amount
                 -------------                                ------
               <S>                                        <C>
               March 31, 2000                             U.S.$ (3,653,390)

               June 30, 2000                              U.S.$(12,113,100)

               September 30, 2000                         U.S.$(17,449,154)

               December 31, 2000                          U.S.$(22,606,002)

               March 31, 2001                             U.S.$(25,675,686)

               June 30, 2001                              U.S.$(27,151,089)

               September 30, 2001                         U.S.$(27,333,601)

               December 31, 2001                          U.S.$(26,306,524)

               March 31, 2002                             U.S.$(24,903,776)
</TABLE>

               Amendment No. 1 to Capital Subscription Agreement

                                      -3-

<PAGE>   4

<TABLE>
<CAPTION>
                  Period Ending                  Amount
                  -------------                  ------
               <S>                          <C>
               June 30, 2002                U.S.$(21,556,744)

               September 30, 2002           U.S.$(16,236,247)

               December 31, 2002            U.S.$ (8,771,888)
</TABLE>

          The amounts set forth above in the first schedule above (as so
     adjusted) shall be referred to in this Agreement as the "Equity Holder
     Commitments" of the Parent Equity Holders. The Parent may from time to
     time, upon not less than 10 days' prior written notice, require that the
     Parent Equity Holders make the New Equity Contributions contemplated hereby
     in advance of any date specified above, and if any such notice is given,
     the Parent Equity Holders shall so make such New Equity Contributions on
     the date and in the amount so required in such notice."

     SECTION 2. Miscellaneous. Except as herein provided, the Amended and
Restated Capital Subscription Agreement shall remain unchanged and in full force
and effect. This Amendment No. 1 may be executed in counterparts which, taken
together, shall constitute a single document and any of the parties hereto may
execute this Amendment No. 1 by signing nay such counterpart. Terms defined in
the Amended and Restated Capital Subscription Agreement are used herein as
defined therein. This Amendment No. 1 shall be governed by and construed in
accordance with the law of the State of New York.

                Amendment No. 1 to Capital Subscription Agreement

                                      -4-
<PAGE>   5
     IN WITNESS WHEREOF, the undersigned have caused this Amendment No. 1 to be
executed by their duly authorized signatures in counterparts all as of the date
first above written.

                                          NEXTEL ARGENTINA S.R.L.

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

                                          NEXTEL INTERNATIONAL (ARGENTINA), LTD.

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

                                          NEXTEL INTERNATIONAL, INC.

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

                Amendment No. 1 to Capital Subscription Agreement

                                      -5-
<PAGE>   6
                       CONSENT AND AGREEMENT TO AMENDMENT

     Pursuant to Section 3(b)(ii) of the Amended and Restated Consent Agreement
dated as of May 12, 1999 between the Parent, the Parent Shareholder and The
Chase Manhattan Bank, as administrative agent (the "Administrative Agent") for
the Lenders party to the Credit Agreement referred to therein, the undersigned
hereby consents to the amendments provided for in this Amendment No. 1.

THE CHASE MANHATTAN BANK

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

                Amendment No. 1 to Capital Subscription Agreement

                                      -6-<PAGE>   1

                                                                    Exhibit 10.1

                                 AMENDMENT NO. 9
                                       TO
                           THIRD AMENDED AND RESTATED
                       CREDIT AND REIMBURSEMENT AGREEMENT

       AMENDMENT No. 9 dated as of May 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, pursuant to Section 5.23 of the Credit Agreement, the Company
and the Banks have agreed to use their respective best efforts to enter into a
restatement of the Credit Agreement on or prior to May 31, 2000 pursuant to
which the obligations of the Company under the Credit Agreement shall be
restructured in a manner satisfactory to the Company and the Banks; and

       WHEREAS, pursuant to Section 2.10(e) of the Credit Agreement, if such
restatement is not entered into on or prior to May 31, 2000, on August 1, 2000
the Commitments under the Credit Agreement shall be automatically and ratably
reduced to $105,000,000 (and, if such restatement is entered into on or prior to
May 31, 2000, on August 1, 2000 the Commitments under the Credit Agreement shall
be automatically and ratably reduced to $125,000,000); and

       WHEREAS, the Banks have requested the Company to provide the Banks with
certain additional information prior to the Banks being in a position to enter
into such restatement;

       WHEREAS, the Company has agreed to provide such additional information;

              NOW, THEREFORE, the parties hereto agree as follows:

<PAGE>   2

       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. 9
Effective Date (as defined in Section 6 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 amended to read
in its entirety as follows:

       "TARGET AMOUNT" means (i) if the Restatement Date has occurred pursuant
to Section 5.23 on or prior to June 7, 2000, $125,000,000 and (ii) otherwise,
$105,000,000.

       SECTION 3. Extension of Date for Execution of the Restatement. The Banks
and the Company acknowledge and agree that the May 31, 2000 date set forth in
Section 5.23 of the Credit Agreement is hereby extended to June 7, 2000.

       SECTION 4. Limitation on New Extensions of Credit. The Company agrees
that neither Company nor any other Borrower shall deliver a Notice of Borrowing
under the Credit Agreement or a request for issuance of a Letter of Credit under
the Credit Agreement or otherwise request any Bank (including the LC Bank) to
extend any credit to the Company or any other Borrower under the Credit
Agreement, and that, notwithstanding any provision of the Credit Agreement
(including Sections 2.01, 2.03 and 3.02), on and after the date hereof, 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 and continuing or converting such Loan on the
terms set forth in such Notice of Interest Rate Election).

       SECTION 5. New York Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of New York.

       SECTION 6. 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. 9
EFFECTIVE DATE") on which the Administrative Agent shall have received:

                                       2
<PAGE>   3

              (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);

              (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;
       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 May 31, 2000.

                                       3
<PAGE>   4

       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

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

                                       4
<PAGE>   5

                                    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:

                                       5
<PAGE>   6

                                    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:

                                       6
<PAGE>   7

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:

                                       7

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