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                                                                  EXECUTION COPY

                           MEMORANDUM OF UNDERSTANDING


            This Memorandum of Understanding ("MOU") is entered into as of this
3rd day of August, 2000 by and among Teleglobe Inc. ("TELEGLOBE"), Teleglobe
Mobile Partners ("TMP"), Orbital Sciences Corporation ("ORBITAL"), Orbital
Communications Corporation ("OCC") and ORBCOMM Global, L.P. ("ORBCOMM").

            WHEREAS, ORBCOMM is engaged in the business of constructing,
operating and marketing a satellite communications system of low-Earth orbit
satellites intended to provide data communications services throughout the world
(the "ORBCOMM SYSTEM");

            WHEREAS, the ORBCOMM System is in commercial service but has not yet
achieved sufficient cash flow to enable it to fund its continuing operations;

            WHEREAS, Teleglobe has been providing capital to ORBCOMM through its
indirect wholly owned subsidiary, TMP, the sole general partner of ORBCOMM, to
fund ORBCOMM's operations;

            WHEREAS, Teleglobe has advised ORBCOMM that it is no longer in a
position to continue to provide equity capital to ORBCOMM;

            WHEREAS, efforts by Teleglobe, TMP, Orbital, OCC and ORBCOMM to
obtain alternative sources of equity funding for ORBCOMM over the past several
months have not yet been successful; and

            WHEREAS, the parties have been engaged in active discussions
concerning how to maintain ORBCOMM's business and preserve the value of the
ORBCOMM System pending receipt of a new equity investment and/or a sale of
ORBCOMM.

            NOW, THEREFORE, in consideration of the foregoing and of the mutual
covenants and agreements hereinafter set forth, the parties hereto hereby
memorialize their mutual understandings as follows:

            1. Business Plan. ORBCOMM, in consultation with Teleglobe and
Orbital, has developed a plan for the ORBCOMM business that contemplates the
continued operation of all critical functions relating to the ORBCOMM System,
the substantial reduction of costs associated with noncore operations and the
termination of nonessential aspects of the business. A copy of such plan (the
"BUSINESS PLAN") is attached hereto as EXHIBIT A. ORBCOMM will devote its
commercially reasonable efforts to the prompt and successful implementation of
the Business Plan, subject to such reasonable
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modifications as may hereafter be developed by ORBCOMM in consultation with and
with prior approval from Teleglobe and Orbital.

            2. Restructuring Arrangements.

               (a) Orbital agrees to continue actively to pursue discussions
with potential investors in ORBCOMM. Orbital further agrees to consider
facilitating the infusion of additional equity into ORBCOMM by issuing a
security of Orbital that would be convertible into an equity interest in
ORBCOMM, with the proceeds of such issuance to be directed to ORBCOMM. Teleglobe
and ORBCOMM agree to support such efforts by Orbital and to cooperate with
Orbital in order to obtain such new equity investment as promptly as
practicable. The parties will endeavor to close a transaction with a new equity
investor on or before September 15, 2000.

               (b) ORBCOMM agrees to work with its creditors to restructure its
debt in a manner consistent with the Business Plan and with the objectives of
any potential new equity investor. In connection therewith, ORBCOMM will (i)
after consultation with Teleglobe and Orbital, engage such investment bankers
and/or other professional advisers/managers as may be appropriate to assist
ORBCOMM in implementing the Business Plan and restructuring its indebtedness,
and (ii) take such other steps as may be appropriate to prepare for an orderly
filing under Chapter 11 of the United States Bankruptcy Code, if necessary, with
the objective of minimizing disruption to the ORBCOMM business. ORBCOMM and
Orbital agree that such a filing may be made at Teleglobe's sole election;
provided that prior to any such filing ORBCOMM shall have received the Interim
Financing (as defined below) and expended such financing substantially in
accordance with the Business Plan.

            3. Teleglobe Financing Arrangements.

               (a) Commencing immediately, Teleglobe will provide or cause to be
provided an aggregate of $17 million of debt financing to ORBCOMM as follows:
interim debt financing, which may be secured consistent with the existing
contractual obligations of ORBCOMM (the "INTERIM FINANCING"), to enable ORBCOMM
to meet payroll, severance, employee benefits, withholding taxes, rent,
utilities and other obligations integral to ORBCOMM's continuing operations in
accordance with the Business Plan, and to pay expenses incurred in preparation
for a potential Chapter 11 filing; and continuing reorganization financing (the
"REORGANIZATION FINANCING"), which may, at Teleglobe's discretion, take the form
of debtor-in-possession financing ("DIP FINANCING"), subject to Bankruptcy Court
approval. (The Interim Financing and the Reorganization Financing are sometimes
hereinafter collectively called the "TELEGLOBE FINANCING".) The Interim
Financing shall be in an aggregate amount of $8 million and shall be provided
under a Bridge

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Credit Agreement substantially in the form attached hereto as EXHIBIT B, under
which ORBCOMM shall be entitled to receive an immediate drawing/advance of
$4,950,000 to be used consistent with the funding requirements identified in the
Business Plan. The remaining amount of $3,050,000 (the "SECOND ADVANCE") shall
be advanced on the business day immediately following the receipt by ORBCOMM of
a fairness opinion relating to the Interim Financing pursuant to the terms of
the Indenture governing the outstanding senior notes of ORBCOMM, with the only
condition to such Second Advance being the receipt of such fairness opinion. The
Reorganization Financing shall be advanced from time to time upon the request of
ORBCOMM consistent with the Business Plan and applicable Bankruptcy Court orders
(if the Reorganization Financing takes the form of DIP Financing), all pursuant
to loan, security and other legal documentation reasonably satisfactory in form
and substance to Teleglobe.

               (b) Teleglobe agrees that, notwithstanding any priority to which
it would otherwise be entitled, Teleglobe will, in conjunction with a
restructuring of ORBCOMM that includes receipt of a new equity infusion and
conversion to equity of all of ORBCOMM's obligations under its procurement
agreements with Orbital, convert or cause to be converted both the Interim
Financing and the Reorganization Financing into ORBCOMM equity, subject to
paragraph 5(b) below; provided, that Teleglobe reserves all of its rights in
respect of recovery of the Interim Financing and Reorganization Financing in
connection with any other restructuring/reorganization (i.e., a sale) of
ORBCOMM.

            4. Dismissal of Teleglobe/BCE Inc. lawsuits. At such time as
Teleglobe has fully funded the $17 million of Teleglobe Financing, Orbital
agrees (a) to dismiss with prejudice the lawsuit filed on June 27, 2000 in the
United States District Court for the Eastern District of Virginia against
Teleglobe and BCE Inc. (the "VIRGINIA ACTION"), (b) to withdraw the demand
letter sent to Teleglobe on June 8, 2000 demanding payment of certain amounts
owing to Orbital under the procurement agreements and (c) to join with
Teleglobe, TMP and OCC in exchanging appropriate mutual releases covering the
claims asserted by Orbital in such demand letter and any similar claims of
Teleglobe or TMP against Orbital or OCC. Pending such dismissal, withdrawal and
exchange of releases (and subject to (A) continuing compliance by Teleglobe and
TMP with the terms of this MOU and (B) the full funding of the Interim Financing
on or before August 15, 2000), (i) neither Orbital nor OCC will take any action
to prosecute the Virginia Action (except that they may, if necessary to preserve
the action, effect service of the Complaint on Teleglobe) or pursue the claims
asserted in the aforementioned demand letter; and (ii) to the extent necessary
to relieve Teleglobe and BCE Inc. from any obligation to file responsive
pleadings in the Virginia Action, Orbital and OCC shall consent to extensions of
time or shall, if necessary, dismiss the Virginia Action without prejudice,
subject, if Orbital and OCC so request, to execution


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by Teleglobe and BCE Inc. of an appropriate tolling agreement extending any and
all limitations periods otherwise applicable to any of the claims asserted in
the Virginia Action.

            5. Implementation of Plan of Reorganization.

               (a) Orbital agrees, in conjunction with the reorganization of
ORBCOMM, (i) to make itself available to serve on ORBCOMM's unsecured creditors'
committee and (ii) if the restructuring/reorganization of ORBCOMM provides for a
new equity infusion (as opposed to a sale of the business), to convert all of
its claims whatsoever against ORBCOMM under Orbital's procurement agreements
with ORBCOMM into equity of the reorganized ORBCOMM.

               (b) Effective upon the implementation of any
restructuring/reorganization plan that provides for conversion of Orbital and
Teleglobe/TMP claims to equity in conjunction with an infusion of additional
equity, as contemplated in paragraphs 3(b) and 5(a), Orbital and Teleglobe will
adjust their equity allocations so that of the combined equity in the
reorganized ORBCOMM received by Orbital upon conversion of its procurement
agreement claims and received by Teleglobe/TMP upon conversion of the Teleglobe
Financing (whatever the level of that combined equity), Orbital will have 60%
and Teleglobe/TMP 40%; provided that Teleglobe/TMP will have no obligation to be
more than a passive investor in the reorganized company, and further provided
that the equity interest in the reorganized ORBCOMM received by Teleglobe/TMP
upon conversion of the Teleglobe Financing shall correspond in all other
respects to the equity interest received by Orbital upon conversion of its
procurement agreement claims.

            6. Employee Retention. ORBCOMM, in consultation with Orbital and
Teleglobe, agrees to take such actions as are reasonably necessary to retain and
motivate key ORBCOMM employees, which may include the establishment of an
ORBCOMM employee stock option plan.

            7. Miscellaneous.

               (a) SUCCESSORS AND ASSIGNS. This MOU and the rights and
obligations set forth herein shall not be assignable by the parties. The
provisions of this MOU shall, except as otherwise provided herein, enure to the
benefit of and be binding upon the parties and their respective successors and
each and every person so bound shall make, execute and deliver all documents
necessary to carry out this MOU.

               (b) PUBLIC ANNOUNCEMENT. Except as provided herein or as required
by law, no press release related to this MOU or the transactions contemplated
herein shall be issued without the joint approval of Teleglobe and Orbital.


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               (c) FURTHER ASSURANCES. Each party shall do such acts and shall
execute such further documents as are within its power as any other party may in
writing at any time and from time to time reasonably request be done or
executed, in order to give full effect to the provisions of this MOU.

               (d) REQUIREMENT OF DEFINITIVE DOCUMENTATION. Each of the parties
hereto agrees that the provisions of Paragraphs 2, 3, 4, 5, and 6 of this MOU do
not contain all material terms that must be agreed upon in order to implement
the arrangements contemplated by such paragraphs and are therefore subject to
the preparation, negotiation and execution of definitive agreements and
documents. Each of the parties hereto agrees to negotiate such definitive
agreements and documents in good faith. This MOU provides the basis upon which
the parties shall negotiate the terms of definitive agreements and documents;
but to the extent that such definitive agreements and documents may be
inconsistent with this MOU, the terms of such definitive agreements and
documents shall take priority.

               (e) GOVERNING LAW. This MOU shall be governed by and construed in
accordance with the laws of the Commonwealth of Virginia (but not including the
choice-of-law rules thereof).

               (f) LIMITATION ON BENEFITS. Paragraphs 3(b), 4 and 5 of this MOU
are solely for the benefit of Teleglobe and Orbital and their respective
affiliates, excepting ORBCOMM. Other than as set forth in Paragraph 4 with
respect to BCE Inc., no third party is entitled to the benefit of any of the
promises made herein or entitled to enforce such provisions against Orbital and
its affiliates or Teleglobe and its affiliates.

               (g) COUNTERPARTS. This MOU may be executed in one or more
counterparts each of which when so executed shall be deemed to be an original
and such counterparts together shall constitute one and the same instrument.


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               (h) IN WITNESS WHEREOF the parties have executed this Memorandum
of Understanding as of the date set out above.

                                    ORBITAL SCIENCES CORPORATION



                                    By:  _____________________________________
                                    Name:  ___________________________________
                                    Title:  __________________________________

                                    ORBITAL COMMUNICATIONS CORPORATION



                                    By:  _____________________________________
                                    Name:  ___________________________________
                                    Title:  __________________________________

                                    TELEGLOBE INC.



                                    By:  _____________________________________
                                         Andre Bourbonnais
                                         Executive Vice President, Chief Legal
                                         Officer and Corporate Secretary

                                    TELEGLOBE MOBILE PARTNERS,
                                    by its General Partner
                                    TELEGLOBE MOBILE INVESTMENT INC.



                                    By:  _____________________________________
                                         Andre Bourbonnais
                                         President

                                    ORBCOMM GLOBAL, L.P.



                                    By:  ____________________________________
                                         Scott Webster
                                         President, Chief Executive Officer


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