EXHIBIT 10.2

SECURITY AGREEMENT

SECURITY AGREEMENT dated as of November 28, 2006, among Motient Corporation, a
Delaware corporation (“Motient”), each of the other parties hereto as a
Guarantor and any entities that may become Guarantors in the future under the
Indenture (as defined below) (the foregoing, collectively, the “Grantors”) in
favor of U.S. Bank, National Association, as the trustee and collateral agent
for the Holders under the Indenture referred to below (in such capacity,
together with its successors in such capacity, the “Collateral Agent”).

The Grantors and U.S. Bank, National Association, as trustee, are parties to an
Indenture dated as of November 28, 2006 (as modified and supplemented and in
effect from time to time, the “Indenture”), providing, subject to the terms and
conditions thereof, for purchase by the Holders of the Securities (as defined in
the Indenture) issued by Motient and a guaranty by the Guarantors of the
obligations as described in Article 10 of the Indenture.

To induce said Holders to purchase the Securities under the Indenture and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the Grantors have agreed to pledge and grant a security
interest in the Collateral (as hereinafter defined) as security for the Secured
Obligations (as hereinafter defined). Accordingly, the parties hereto agree as
follows:

Section 1.      Definitions, Etc.

1.01.   Terms Generally. Terms used herein and not otherwise defined herein are
used herein as defined in the Indenture.

1.02.   Certain UCC Terms. The terms “Accounts”, “Chattel Paper”, “Document”,
“Electronic Chattel Paper”, “Equipment”, “General Intangible”, “Goods”,
“Instrument”, “Inventory”, “Investment Property”, “Payment Intangible”,
“Proceeds” and “Software” have the respective meanings ascribed thereto in
Article 9 of the NYUCC.

1.03.   Additional Definitions. In addition, as used herein:

“ATC License” means the Amended and Restated Intellectual Property Assignment
and License Agreement dated May 11, 2005 by and between ATC Technologies, LLC, a
Delaware limited liability company, and TerreStar.

“Cash Escrow Account” means account number 107145001 maintained with the
Collateral Agent.

“Collateral” has the meaning ascribed thereto in Section 3.

“Copyright Collateral” means all Copyrights, whether now owned or hereafter
acquired by the Grantors, including each Copyright identified in Annex 4 (Part
C) and all Copyright Licenses.

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“Copyrights” means all domestic and foreign copyrights, whether registered or
not, including, without limitation, all copyright rights throughout the universe
(whether now or hereafter arising) in any and all media (whether now or
hereafter developed), in and to all original works of authorship fixed in any
tangible medium of expression, acquired or used by the Grantor, all
applications, registrations and recordings thereof (including, without
limitation, applications, registrations and recordings in the United States
Copyright Office or in any similar office or agency of the United States or any
other country or any political subdivision thereof), including, without
limitation, copyrights in computer software, programs and databases (including,
without limitation, source code, object code and all related applications and
data files, firmware and documentation and materials relating thereto, and any
substitutions, replacements, improvements, error corrections, updates and new
versions of any of the foregoing, but excluding, “shrink-wrap” computer
software, programs and databases), internet web sites, whether registered or
unregistered all registrations and applications for registration for any of the
foregoing, together with all reissues, divisions, continuations,
continuations-in-part, extensions, renewals and reexaminations thereof.

“Copyright Licenses”means any written agreement naming any Grantor as licensee
(including, without limitation, those identified in Annex 4), granting any right
under any Copyright, including, without limitation, the grant of rights to
manufacture, distribute, exploit and sell materials derived from any Copyright.

“Excluded Property” means (a)(i) 25,478,273 shares of common stock of Skyterra
to be distributed to Motient’s common shareholders and (ii) 4,447,801 shares of
common stock of Skyterra that would be acquired upon conversion of limited
partnership interests in Mobile Satellite Ventures, L.P. and that would be
distributed to Motient’s preferred shareholders upon the conversion of their
preferred shares pursuant to and in accordance with the Exchange Agreement and
the Registration Rights Agreement, (b) the shares of common stock of TerreStar
Networks Bermuda Ltd. and (c) the limited partnership units of Mobile Satellite
Ventures, L.P. and the common stock of Mobile Satellite Ventures GP, Inc.;
provided, however, that shares of common stock of Skyterra issuable upon the
conversion or exchange of such limited partnership units or common stock are not
Excluded Property unless they constitute Excluded Property pursuant to clause
(a)(ii) of this definition.

“FCC” means the Federal Communications Commission.

“FCC License”: any license, authorization, approval, or permit granted by the
FCC pursuant to the Communications Act of 1934, as amended, to the Issuer or its
Restricted Subsidiaries, or assigned or transferred to the Issuer or its
Subsidiaries pursuant to FCC consent, in each case for or in connection with the
construction and/or operation of any satellite system. “FCC License” includes
the U.S. FCC Letter of Intent. “FCC License Rights” means any right, title or
interest in, to or under any FCC License, whether directly or indirectly held,
including, without limitation, any rights owned, granted, approved or issued
directly or indirectly by the FCC or held, leased, licensed or otherwise
acquired from or through any party.

“IP Collateral” means, collectively, (a) all Copyright Collateral, (b) all
Patent Collateral, (c) all Trademark Collateral, (d) all confidential and
proprietary information, including, without limitation, know-how, trade secrets,
manufacturing and production processes and techniques, inventions, research and
development

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information, databases and data, including, without limitation, technical data,
(e) all tangible embodiments of any of the foregoing and all rights
corresponding thereto throughout the world, and (f) any and all claims for
damages and injunctive relief for past, present and future infringement,
dilution, misappropriation, violation, misuse or breach with respect to any of
the foregoing, with the right, but not the obligation, to sue for and collect,
or otherwise recover, such damages.

“Motor Vehicles” means motor vehicles, tractors, trailers and other like
property, whether or not the title thereto is governed by a certificate of title
or ownership.

“NYUCC” means the Uniform Commercial Code as in effect from time to time in the
State of New York.

“Patent Collateral” means all Patents, whether now owned or hereafter acquired
by the Grantors, including each Patent identified in Annex 4 and all Patent
Licenses.

“Patent License” means all written agreements providing for the grant to any
Grantor of any right to manufacture, use or sell any invention covered in whole
or in part by a Patent, including, without limitation, any of the foregoing
identified in Annex 4.

“Patents” means all patents, patent applications, all inventions claimed or
disclosed therein and all improvements thereto, all registrations and
applications for registration for any of the foregoing, together with all
reissues, divisions, continuations, continuations-in-part, extensions and
reexaminations thereof.

“Pledged Equity” means the Equity Interests in the Share Issuers (as
supplemented from time to time pursuant to any supplement effecting such pledge)
under the name of the Grantors and all other shares of capital stock, or
partnership and other ownership interest, of whatever class or character of any
Share Issuer, now or hereafter owned by the Grantors, and all certificates
evidencing the same (but (A) not more than 65% of all shares of each class of
capital stock of any Foreign Subsidiary and (B) excluding the Excluded
Property).

“Secured Obligations” means all obligations of every nature of each Grantor from
time to time owed to the Collateral Agent, the Trustee or any Holder under any
Financing Document, whether for principal, interest (including interest which,
but for the filing of a petition in bankruptcy with respect to such Grantor,
would have accrued on any obligation, whether or not a claim is allowed against
such Grantor for such interest in the related bankruptcy proceeding), expenses,
indemnities or any other amount.

“Share Issuer” means any Person in which a Grantor owns Equity Interests,
whether now or hereafter existing or acquired, including, without limitation,
the respective corporations, partnerships or other entities identified next to
the names of the Grantors on Annex 3 under the caption “Share Issuer”.

“Side Letter” means the agreements between TMI and TerreStar relating to the
transfer of the Letter of Intent and the T-1 satellite.

“Trademark Collateral” means all Trademarks, whether now owned or hereafter
acquired by the Grantors, including each Trademark identified in Annex 4,
together, in each case, with the goodwill of the business connected with the use
of, and symbolized by, each such trade name, trademark and service mark and all

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Trademark Licenses. Notwithstanding the foregoing, the Trademark Collateral does
not and shall not include any Trademark that would be rendered invalid,
abandoned, void or unenforceable by reason of its being included as part of the
Trademark Collateral.

“Trademark License” means any written agreement providing for the grant to any
Grantor of any right to use any Trademark, including, without limitation, any of
the foregoing identified in Annex 4.

“Trademarks” means all domestic and foreign trade names, trademarks and service
marks, logos, domain names, trade dress, designs, slogans, business names,
corporate names and other source identifiers, whether registered or
unregistered, all registrations and applications for registration for any of the
foregoing, together with all modifications, extensions and renewals thereof.

Section 2.      Representations and Warranties. Each Grantor represents and
warrants to the Holders as of the date hereof that:

(a) Title. Each Grantor is the legal and beneficial owner, lessee or licensee of
the Collateral in which it purports to grant a security interest pursuant to
Section 3 and no Lien exists upon such Collateral, except for (i) the pledge and
security interest in favor of the Collateral Agent for the benefit of the
Holders created or provided for herein and (ii) Liens permitted under the
Indenture. Upon filing of the appropriate financing statements, the pledge and
security interest in favor of the Collateral Agent for the benefit of the
Holders created or provided for herein will constitute a valid first priority
perfected pledge and security interest in and to all of such Collateral to the
extent a security interest can be perfected by filing.

(b) Names, Etc. The full and correct legal name, type of organization,
jurisdiction of organization, organizational ID number (if applicable) and
mailing address of the Grantors as of the date hereof (or on the date that such
Grantor becomes a party hereto) are correctly set forth in Annex 1. Annex 1
correctly specifies the place of business of the Grantors or, if a Grantor has
more than one place of business, the location of the chief executive office of
such Grantor.

(c) Changes in Circumstances. Such Grantor has not (i) within the period of four
months prior to the date hereof (or on the date that such Grantor becomes a
party hereto), changed its location (as defined in Section 9-307 of the NYUCC),
(ii) except as specified in Annex 1, heretofore changed its name, or (iii)
except as specified in Annex 2, heretofore become a “new debtor” (as defined in
Section 9-102(a)(56) of the NYUCC) with respect to a currently effective
security agreement previously entered into by any other Person.

(d) Pledged Equity. The Pledged Equity identified in Annex 3 hereto constitutes
all of the issued and outstanding Equity Interests of all classes of Equity
Interests of each Share Issuer beneficially owned by each Grantor on the date
hereof (or will be updated to correctly identify at such time on the date such
Grantor becomes a party hereto to correctly identify at such time) (but (A) not
in excess of 65% of the issued and outstanding shares of any class of the Equity
Interests of any Foreign Subsidiary and (B) excluding the Excluded Property),
whether or not registered in the name of the Grantor (or, in the case of any
supplement to said Annex 3 upon the execution and delivery of a supplement
effecting such pledge, as of the date of such

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supplement). Annex 3 hereto correctly identifies, as at the date hereof (or on
the date such Grantor becomes a party hereto), with respect to each Share
Issuer, (i) each class of Equity Interests to the extent that it constitutes
Collateral, (ii) the number of shares, units or other divisions of interests of
such Equity Interests that are authorized and outstanding, (iii) whether such
Equity Interests are certificated, a description of any such certificates and
the number of shares, units or other interests represented by such certificates
and (iv) and the registered owner, or other owner or holder thereof. The Pledged
Equity identified under the name of each Grantor in Annex 3 is, and all other
Pledged Equity in which the Grantors shall hereafter grant a security interest
pursuant to this Security Agreement or any supplement hereto will be (A) duly
authorized, validly existing, fully paid and non-assessable (in the case of any
equity interest in a corporation), (B) legal, valid and binding obligations of
the Grantors (in the case of any equity interest in a partnership) and (C) duly
issued and outstanding (in the case of any equity interest in any other entity).

(e) Intellectual Property. Annex 4 (Part A) hereto sets forth a complete and
correct list of all registered (and applications for registration of) Trademarks
owned by the Grantors on the date hereof. Annex 4 (Part B) hereto sets forth a
complete and correct list of all granted (and applications for grant of) Patents
owned by the Grantors on the date hereof. Annex 4 (Part C) hereto sets forth a
complete and correct list of all registered (and applications for registration
of) Copyrights owned by the Grantors on the date hereof. Except to the extent as
would not have a Material Adverse Effect and except pursuant to licenses and
other agreements entered into by the Grantors in the ordinary course of
business, each Grantor is either the owner of all right, title and interest in
and to its IP Collateral or has been granted all necessary license rights in and
to its IP Collateral and, except for trademark applications based on
intent-to-use which have not yet been allowed by the U.S. Patent and Trademark
Office, is entitled to use all its IP Collateral. Except to the extent as would
not have a Material Adverse Effect, all of the IP Collateral, to the Grantor’s
knowledge, is valid and enforceable and, except as may be set forth in said
Annex 4 and except to the extent as would not have a Material Adverse Effect,
all registrations, to the best of such Grantor's knowledge, listed in Annex 4
are valid, subsisting and in full force and effect. With respect to each
material item of IP Collateral either owned or exclusively licensed by any
Grantor and as each Grantor deems necessary, in its reasonable business
judgment, for the conduct of its business, each Grantor has made or performed
all commercially reasonable filings, recordings and other acts and has paid all
required fees and taxes necessary to maintain and protect its interest in full
force and effect where required for its business, and to protect and maintain
its interest therein including, without limitation, any necessary recordations
of any of its interests in the Patents and Trademarks with the U.S. Patent and
Trademark Office and to the extent commercially desirable and deemed necessary
by each Grantor, in its reasonable business judgment, for the conduct of its
business, in corresponding national and international patent offices, and any
necessary recordation of any of its interests in the Copyrights with the U.S.
Copyright Office and to the extent commercially desirable and deemed necessary
by each Grantor, in its reasonable business judgment, for the conduct of its
business, in corresponding national and international copyright offices except
where any failure to make such filings and payments would not have a Material
Adverse Effect. To the best of such Grantor’s knowledge, the operation of each
Grantor’s business as currently conducted or as contemplated to be conducted and
the use of the IP Collateral in connection therewith do not conflict with,
infringe, misappropriate, dilute, misuse or otherwise violate the intellectual
property rights of any third party in any material respect, except to the extent
that would not have a Material Adverse Effect. Except as described in Annex 4,
no claim,

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action, suit, investigation, litigation or proceeding is pending or, to the
knowledge of each Grantor, threatened against such Grantor (i) based upon or
challenging or seeking to deny or restrict the Grantor’s rights in or of any of
the IP Collateral, (ii) alleging that the Grantor’s rights in or use of the IP
Collateral or that any services provided by, processes used by, or products
manufactured or sold by, such Grantor infringe, misappropriate, dilute, misuse
or otherwise violate any Patent, Trademark, Copyright or any other intellectual
property right of any third party, or (iii) alleging that the IP Collateral is
being licensed or sublicensed in violation or contravention of the terms of any
license or other agreement.

(f) Material Licenses; Trademarks. Annex 4 hereto sets forth a complete and
correct list of all material licenses included in the IP Collateral on the date
hereof. The Grantors do not currently own any Trademarks registered in the
United States of America to which the sentence of the definition of Trademark
Collateral applies.

(g) Commercial Tort Claims. Annex 5 sets forth a complete and correct list of
commercial tort claims of the Grantors in existence on the date hereof.

Section 3.      Collateral. As collateral security for the prompt payment in
full when due (whether at stated maturity, by acceleration or otherwise) of the
Secured Obligations, each the Grantors hereby pledges and grants to the
Collateral Agent for the ratable benefit of the Holders, a security interest in
all of such Grantor’s right, title and interest in the following, whether now
owned or hereafter acquired by such Grantor and whether now existing or
hereafter coming into existence and wherever located (all of the following being
collectively referred to herein as “Collateral”):

(a) all Accounts, Instruments, Documents, Chattel Paper (whether tangible or
electronic), Inventory, Equipment, Goods, Payment Intangibles, Software and
other General Intangibles (including, without limitation, the TerreStar note
referred to in Section 4.06 of the Indenture, the Side Letter, the ATC License,
the Hughes Agreement and the Satellite Construction Agreement);

(b) all Investment Property, including all Pledged Equity;

(c) all IP Collateral, and the right to recover for past, present and future
infringements or misappropriations thereof and all other rights of any kind
whatsoever accruing thereunder or pertaining thereto;

(d) all Payment Intangibles, Software and all other General Intangibles
whatsoever not covered by the preceding clauses of this Section 3;

(e) all commercial tort claims, as defined in Section 9-102(a)(13) of the NYUCC,
arising out of the events described in Annex 5;

(f) all FCC License Rights, whether now owned or held or hereafter acquired or
held by a Grantor, including all FCC Licenses, including, without limitation,
the right to receive monies, proceeds, or other consideration in connection with
the sale, assignment, transfer, or other disposition of any FCC Licenses, the
proceeds from the sale of any FCC Licenses or any goodwill or other intangible
rights or benefits associated therewith, including without limitation all right
of each Grantor to (A) transfer, assign or otherwise dispose of

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its rights, title and interests, if any, under or in respect of such FCC
Licenses, (B) exercise any rights, demands and remedies against the lessor,
licensor or other parties thereto, and (C) all rights of such Grantor to receive
proceeds of any insurance, indemnities, warranties, guaranties or claims for
damages in connection therewith; provided, that such security interest does not
include at any time any FCC License to the extent (but only to the extent) that
at such time the Collateral Agent may not validly possess a security interest
directly in the FCC License pursuant to applicable Federal law, including the
Communications Act of 1934, as amended, and the rules, regulations and policies
promulgated thereunder, as in effect at such time, but such security interest
does include at all times all proceeds of the FCC Licenses, and the right to
receive all monies, consideration and proceeds derived from or in connection
with the sale, assignment, transfer, or other disposition of the FCC Licenses;

(g) the Cash Escrow Account and all cash and Investment Property from time to
time credited thereto;

(h) to the extent related to any of the foregoing, all books, correspondence,
credit files, records, invoices and other papers (including without limitation
all tapes, cards, computer runs and other papers and documents in the possession
or under the control of the Grantors or any computer bureau or service company
from time to time acting for the Grantors); and

(i) all Proceeds, products, offspring, accessions, rents, profits, income,
benefits, royalties and other payments now or hereafter due and payable with
respect to, and supporting obligations relating to, any and all of the
Collateral, and all substitutions and replacements of and to any of the
Collateral, including, without limitation, proceeds, collateral and supporting
obligations that constitute property of the types described in clauses (a)
through (h) of this Section 3.

IT BEING UNDERSTOOD, HOWEVER, that:

(A) in no event shall the security interest granted under this Section 3 attach
to any lease, license, contract, Intellectual Property or agreement to which any
Grantor is a party (or to any of its rights or interests thereunder) or
Investment Property to the extent that the grant of such security interest
would: (x) constitute or result in either (i) the abandonment, invalidation or
unenforceability of any right, title or interest of the Grantors therein; or
(ii) a breach or termination pursuant to the terms of, or a default under, any
such lease, license, contract, property rights or agreement (other than, to the
extent that any such term would be rendered ineffective pursuant to Sections
9-406, 9-407, 9-408 or 9-409 of the NYUCC); or (y) require the consent of any
third party;

(B) in no event shall the security interest granted under this Section 3 attach
to any leasehold interest in real property;

(C) notwithstanding anything to the contrary set forth herein, in no event shall
more than 65% of all shares of each class of capital stock of any Foreign
Subsidiary or any asset of a Foreign Subsidiary be included in Collateral;

(D) to the extent that the terms of any Indebtedness incurred to finance the
acquisition of any property (other than any property obtained pursuant to the
Satellite Construction Agreement or the Arianespace Agreement) expressly
prohibits the pledge, assignment or transfer thereof, or the grant of a security

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interest therein, the applicable Grantor’s right, title and interest in such
property shall be excluded from the Collateral for so long as such prohibition
continues; and

(E) no security interest shall attach to any Excluded Property;

provided, that, notwithstanding anything to the contrary, clause (A) shall apply
only to the extent that any provisions providing for the breach, termination or
default with respect to such lease, license, contract or agreement were not in
contemplation of this Security Agreement or any of the transactions contemplated
by the Indenture; and provided further that immediately upon the
ineffectiveness, lapse or termination of any such prohibition on the grant of
such security interest or lien, the Collateral shall include, and such Grantor
shall be deemed to have granted a security interest in, all such right, title
and interests as if such prohibition had never been in effect.

Section 4.      Proceeds of Accounts. If so requested by the Collateral Agent at
any time after the occurrence and during the continuance of an Event of Default,
the Grantors shall instruct all account debtors in respect of Accounts, Chattel
Paper and General Intangibles and all obligors on Instruments to make all
payments in respect thereof either (i) directly to the Collateral Agent (by
instructing that such payments be remitted to a post office box which shall be
in the name and under the control of the Collateral Agent) or (ii) to one or
more other banks in the United States of America (by instructing that such
payments be remitted to a post office box which shall be in the name and under
the control of the Collateral Agent) under arrangements, in form and substance
satisfactory to the Collateral Agent, pursuant to which the Grantors shall have
irrevocably instructed such other bank (and such other bank shall have agreed)
to remit all proceeds of such payments directly to the Collateral Agent.
Notwithstanding anything herein to the contrary, in no event shall the Grantors
be required to obtain any control agreements with respect to any deposit account
or securities account of a Grantor or otherwise perfect the Lien granted
hereunder in any deposit account or securities account, except to the extent
expressly specified in Section 5.01(a)(y) .

Section 5.      Further Assurances; Remedies. In furtherance of the grant of the
pledge and security interest pursuant to Section 3, each Grantor hereby agrees
with each Holder and the Collateral Agent as follows:

5.01.   Delivery and Other Perfection. Each Grantor shall:

(a) if any of the Pledged Equity or other Investment Property pledged by the
Grantors under clause (b) of Section 3 in an aggregate amount in excess of
$1,000,000 is received by the Grantors, forthwith either (x) deliver to the
Collateral Agent such Pledged Equity or other Investment Property (together with
the certificates or instruments for any such Pledged Equity or other Investment
Property duly endorsed in blank or accompanied by such instruments of assignment
and transfer in such form and substance as the Collateral Agent may request),
all of which thereafter shall be held by the Collateral Agent, pursuant to the
terms of this Agreement, as part of the Collateral, (y) cause the applicable
securities intermediary or securities intermediaries to enter into account
control agreements with the Collateral Agent in form and substance reasonably
satisfactory to the Collateral Agent or cause all securities accounts to be
maintained with the financial institution acting as Collateral Agent, or (z)
take such other action as the Collateral Agent shall reasonably deem necessary
or

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appropriate to duly record or otherwise perfect the Lien created hereunder in
such Pledged Equity or other Investment Property pursuant to said clause (b)
under the law of the United States or a jurisdiction thereof;

(b) deliver and pledge to the Collateral Agent any and all Instruments in an
aggregate amount in excess of $1,000,000, endorsed and/or accompanied by such
instruments of assignment and transfer in such form and substance as the
Collateral Agent may reasonably request; provided that (other than in the case
of any intercompany notes) so long as no Event of Default shall have occurred
and be continuing, the Grantors may retain for collection in the ordinary course
any Instruments received by the Grantors in the ordinary course of business and
the Collateral Agent shall, promptly upon request of either Grantor, make
appropriate arrangements for making any Instrument pledged by the Grantors
available to the Grantors, for purposes of presentation, collection or renewal
(any such arrangement to be effected, to the extent deemed appropriate by the
Collateral Agent, against trust receipt or like document);

(c) give, execute, deliver, file, record, authorize or obtain all such financing
statements, notices, instruments, documents, agreements or consents or other
papers and take all such other actions as may be necessary or desirable (in the
reasonable judgment of the Collateral Agent) and reasonably requested by the
Collateral Agent to create, preserve, perfect or validate the security interest
granted pursuant hereto under the law of the United States or a jurisdiction
thereof or to enable the Collateral Agent to exercise and enforce its rights
hereunder with respect to such pledge and security interest, including, without
limitation, (i) (A) making filings, registrations and recordations with the U.S.
Patent and Trademark Office and the U.S. Copyright Office, (B) delivery of all
original certificates representing Pledged Equity, together with indorsements,
stock powers or other appropriate instruments of transfer, duly executed or
endorsed in blank, and (C) taking all such action as may be required by the
Uniform Commercial Code then in effect in any applicable jurisdiction in order
to effect to the same, and (ii) following the occurrence and during the
continuance of an Event of Default, (A) causing any or all of the Pledged Equity
to be transferred of record into the name of the Collateral Agent or its nominee
(and the Collateral Agent agrees that if any Pledged Equity is transferred into
its name or the name of its nominee, the Collateral Agent will thereafter
promptly give to the Grantors copies of any notices and communications received
by it with respect to the Pledged Equity pledged by the Grantors hereunder, and
(B) if requested by the Collateral Agent, using commercially reasonable efforts
to obtain any consents, authorization and approvals of the FCC in connection
with any transfer or disposition of any FCC License or the Equity Interests of
any Share Issuer that owns or holds any rights with respect to any FCC License,
including, without limitation, as provided in Section 6.09;

(d) in no event shall the Grantors be required to perfect the security interest
granted pursuant hereto in any Motor Vehicle;

(e) keep full and accurate books and records relating to the Collateral;

(f) if any Event of Default shall have occurred and be continuing, permit
representatives of the Collateral Agent, upon reasonable notice, at any time
during normal business hours to inspect and make abstracts from its books and
records pertaining to the Collateral, and permit representatives of the
Collateral Agent to be present at the Grantors’ respective places of business to
receive copies of all communications

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and remittances relating to the Collateral, and forward copies of any notices or
communications received by the Grantors with respect to the Collateral, all in
such manner as the Collateral Agent may require; and

(g) execute and deliver and, subject to the execution thereof by the Collateral
Agent, upon request of the Collateral Agent cause to be filed, such continuation
statements, and do such other acts and things as the Collateral Agent may
reasonably request, as may be necessary to maintain the perfection of the
security interest granted pursuant hereto under the law of the United States or
a jurisdiction therein;

(h) upon the occurrence and during the continuance of any Default, upon request
of the Collateral Agent, promptly notify (and the Grantors hereby authorize the
Collateral Agent so to notify) each account debtor in respect of any Accounts or
Instruments that such Collateral has been assigned to the Collateral Agent
hereunder, and that any payments due or to become due in respect of such
Collateral are to be made directly to the Collateral Agent.

5.02.   Other Financing Statements and Liens. Except as otherwise permitted
under the Indenture, no Grantor shall file or suffer to be on file, or authorize
or permit to be filed or to be on file, in any jurisdiction, any financing
statement or like instrument with respect to the Collateral in which the
Collateral Agent is not named as the sole secured party for the benefit of the
Holders.

5.03.   Preservation of Rights. The Collateral Agent shall not be required to
take steps necessary to preserve any rights against prior parties to any of the
Collateral.

5.04.   Special Provisions Relating to Certain Collateral.

(a) Special Provisions Relating to Pledged Equity.

(i) The Grantors will cause the Pledged Equity to constitute at all times 100%
of all Equity Interests of each Share Issuer then outstanding owned by the
Grantors (but no more than 65% of each class of the outstanding Equity Interests
of any Foreign Subsidiary of the Grantors and excluding the Excluded Property).

(ii) So long as no Event of Default shall have occurred and be continuing, the
Grantors shall have the right to exercise all voting, consensual and other
powers of ownership pertaining to the Pledged Equity for all purposes not
inconsistent with the terms of this Security Agreement, the Indenture or any
document, agreement, supplement or other instrument or agreement referred to
herein or therein or contemplated thereby or hereby, provided that the Grantors
agree that they will not vote the Pledged Equity in any manner that is
inconsistent with the terms of this Security Agreement or any other Financing
Document; and the Collateral Agent shall execute and deliver to the Grantors or
cause to be executed and delivered to the Grantors all such proxies, powers of
attorney, dividend and other orders, and all such instruments, without recourse,
as the Grantors may reasonably request for the purpose of enabling the Grantors
to exercise the rights and powers which they are entitled to exercise pursuant
to this Section 5.04(a)(ii) .

(iii) Unless and until an Event of Default shall have occurred and be
continuing, or the principal of and interest on the Securities, and all other
amounts outstanding under the Indenture shall have been

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11

declared (or become) due and payable, the Grantors shall be entitled to receive
and retain any dividends, distributions or proceeds on the Pledged Equity paid
in cash out of earned surplus.

(iv) If any Event of Default shall have occurred and be continuing, and whether
or not the Holders exercise any available right to declare any Secured
Obligations due and payable or seek or pursue any other relief or remedy
available to them under applicable law or under this Agreement, the Financing
Documents or any other agreement relating to such Secured Obligation, upon
request by the Collateral Agent, all dividends and other distributions on the
Pledged Equity shall be paid directly to the Collateral Agent, and, if the
Collateral Agent shall so request in writing, the Grantors jointly and severally
agree to execute and deliver to the Collateral Agent appropriate additional
dividend, distribution and other orders and documents to that end, provided that
if such Event of Default is cured, any such dividend or distribution theretofore
paid to the Collateral Agent shall, upon request of any Grantor (except to the
extent theretofore applied to the Secured Obligations), be returned by the
Collateral Agent to the Grantors.

(b) Special Provisions Relating to IP Collateral.

(i) For the purpose of enabling the Collateral Agent to exercise rights and
remedies under Section 5.05 at such time as the Collateral Agent shall be
lawfully entitled to exercise such rights and remedies, and for no other
purpose, the Grantors hereby grant to the Collateral Agent, to the extent
assignable, an irrevocable, non-exclusive license (exercisable without payment
of royalty or other compensation to the Grantors) to use, assign, license or
sublicense any of the IP Collateral now owned or hereafter acquired by the
Grantors, wherever the same may be located, including in all cases with
reasonable access to all media in which any of the licensed items may be
recorded or stored and to all computer programs used for the compilation or
printout thereof.

(ii) Notwithstanding anything contained herein to the contrary, but subject to
the provisions of the Indenture that limit the right of the Grantors to dispose
of their property, so long as no Event of Default shall have occurred and be
continuing, the Grantors will be permitted to exploit, use, enjoy, protect,
license, sublicense, assign, sell, dispose of or take other actions with respect
to the IP Collateral in the ordinary course of the business of the Grantors. In
furtherance of the foregoing, unless an Event of Default shall have occurred and
be continuing the Collateral Agent shall from time to time, upon the request of
any Grantor, execute and deliver any instruments, certificates or other
documents, in the form so requested, that the Grantors shall have certified are
appropriate (in their judgment) to allow them to take any action permitted above
(including relinquishment of the license provided pursuant to clause (i)
immediately above as to any specific IP Collateral). Further, upon the payment
in full of all of the Secured Obligations, or earlier expiration of this
Agreement or release of the Collateral, the license granted pursuant to clause
(i) immediately above shall automatically terminate. The exercise of rights and
remedies under Section 5.05 by the Collateral Agent shall not terminate the
rights of the holders of any licenses or sublicenses theretofore granted by the
Grantors in accordance with the first sentence of this clause (ii).

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(c) Special Provisions Relating to the Cash Escrow Account

(i) Upon the date hereof, Motient is delivering to the Collateral Agent a
control agreement covering the Collateral Escrow Account. At all times prior to
May 30, 2007, the Collateral Agent shall have sole and exclusive dominion and
control over the Cash Escrow Account and none of the cash or Investment Property
from time to time credited to the Collateral Escrow Account shall be withdrawn,
subject to clauses (ii) and (iii) below. Notwithstanding the foregoing, Motient
shall be entitled to direct the investment of funds in the Collateral Escrow
Account into Cash Equivalents, provided that all such Cash Equivalents shall
mature prior to May 30, 2007.

(ii) On May 30, 2007, (or such earlier date on which the Securities are redeemed
in full) the funds in the Cash Escrow Account shall be applied to the payment of
interest on the Securities. Any excess amount remaining in the Cash Escrow
Amount after such application shall be returned to Motient.

(iii) If (A) the outstanding principal amount of the Securities is reduced at
any time prior to May 30, 2007 and (B) as a consequence of such reduction the
amount of funds in the Cash Escrow Account exceeds the amount required to be
held in such account pursuant to the Indenture, then the amount of such excess
shall continue to be held in the Cash Escrow Account.

5.05.   Events of Default, Etc. During the period during which an Event of
Default shall have occurred and be continuing:

(a) the Grantors shall, at the request of the Collateral Agent, assemble the
Collateral owned by them at such place or places, reasonably convenient to the
Collateral Agent and the Grantors, designated in the Collateral Agent’s request;

(b) the Collateral Agent may make any reasonable compromise or settlement deemed
desirable with respect to any of the Collateral and may extend the time of
payment, arrange for payment in installments, or otherwise modify the terms of,
any of the Collateral;

(c) the Collateral Agent shall have all of the rights and remedies with respect
to the Collateral of a secured party under the NYUCC (whether or not the Uniform
Commercial Code is in effect in the jurisdiction where the rights and remedies
are asserted) and such additional rights and remedies to which a secured party
is entitled under the laws in effect in any jurisdiction where any rights and
remedies hereunder may be asserted, including, without limitation, the right, to
the maximum extent permitted by law, to exercise all voting, consensual and
other powers of ownership pertaining to the Collateral as if the Collateral
Agent were the sole and absolute owner thereof (and the Grantors agree to take
all such action as may be appropriate to give effect to such right);

(d) the Collateral Agent in its discretion may, in its name or in the name of
the Grantors or otherwise, demand, sue for, collect or receive any money or
property at any time payable or receivable on account of or in exchange for any
of the Collateral, but shall be under no obligation to do so; and

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13

(e) the Collateral Agent may, upon ten Business Days’ prior written notice to
the Grantors of the time and place (which the Grantors agree constitutes
reasonable prior notice), with respect to the Collateral or any part thereof
which shall then be or shall thereafter come into the possession, custody or
control of the Collateral Agent, the holders of the Secured Obligations or any
of their respective agents, sell, lease, assign or otherwise dispose of all or
any part of such Collateral, at such place or places as the Collateral Agent
deems best, and for cash or for credit or for future delivery (without thereby
assuming any credit risk), at public or private sale, without demand of
performance or notice of intention to effect any such disposition or of the time
or place thereof (except such notice as is required above or by applicable
statute and cannot be waived), and the Collateral Agent or any holder of any
Secured Obligation or anyone else may be the purchaser, lessee, assignee or
recipient of any or all of the Collateral so disposed of at any public sale (or,
to the extent permitted by law, at any private sale) and thereafter hold the
same absolutely, free from any claim or right of whatsoever kind, including any
right or equity of redemption (statutory or otherwise), of the Grantors, any
such demand, notice and right or equity being hereby expressly waived and
released. In the event of any sale, assignment, or other disposition of any of
the IP Collateral, the goodwill connected with and symbolized by the IP
Collateral subject to such disposition shall be included. The Collateral Agent
may, without notice or publication, adjourn any public or private sale or cause
the same to be adjourned from time to time by announcement at the time and place
fixed for the sale, and such sale may be made at any time or place to which the
sale may be so adjourned. The proceeds of each collection, sale or other
disposition under this Section 5.05, including by virtue of the exercise of the
license granted to the Collateral Agent in Section 5.04(b), shall be applied in
accordance with Section 5.08. The Grantors recognize that, by reason of certain
prohibitions contained in the Securities Act of 1933, as amended, and applicable
state securities laws, the Collateral Agent may be compelled, with respect to
any sale of all or any part of the Collateral, to limit purchasers to those who
will agree, among other things, to acquire the Collateral for their own account,
for investment and not with a view to the distribution or resale thereof. The
Grantors acknowledge that any such private sales may be at prices and on terms
less favorable to the Collateral Agent than those obtainable through a public
sale without such restrictions, and, notwithstanding such circumstances, agree
that any such private sale shall be deemed to have been made in a commercially
reasonable manner and that the Collateral Agent shall have no obligation to
engage in public sales and no obligation to delay the sale of any Collateral for
the period of time necessary to permit the respective issuer thereof to register
it for public sale. The Collateral Agent shall not be required to marshal any
present or future collateral security (including, but not limited to, this
Agreement and the Collateral) for, or other assurances of payment of, the
Secured Obligations or any of them or to resort to such collateral security or
other assurances of payment in any particular order, and all of the Collateral
Agent’s rights hereunder and in respect of such collateral security and other
assurances of payment shall be cumulative and in addition to all other rights,
however existing or arising. To the extent that each Grantor lawfully may, the
Grantor hereby agrees that it will not invoke any law relating to the
marshalling of collateral which might cause delay in or impede the enforcement
of the Collateral Agent’s rights under this Agreement or under any other
instrument creating or evidencing any of the Secured Obligations or under which
any of the Secured Obligations is outstanding or by which any of the Secured
Obligations is secured or payment thereof is otherwise assured, and, to the
extent that it lawfully may, the Grantor hereby irrevocably waives the benefits
of all such laws. Each Grantor hereby acknowledges that if the Collateral Agent
complies with any applicable state, provincial, or federal law requirements in
connection with a disposition of the Collateral, such compliance will not
adversely affect the commercial reasonableness of any sale or other disposition
of the Collateral.

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14

5.06.   Locations; Names. Without at least 10 days’ prior written notice to the
Collateral Agent, no Grantor shall change its location (as defined in Section
9-307 of the Uniform Commercial Code) or change its name from the name shown as
its current legal name on Annex 1.

5.07.   Private Sale. The Collateral Agent and the Holders shall incur no
liability as a result of the sale of the Collateral, or any part thereof, at any
private sale pursuant to Section 5.05 conducted in a commercially reasonable
manner.

5.08.   Application of Proceeds. Except as otherwise herein expressly provided
and except as provided below in this Section 5.08, the Proceeds of any
collection, sale or other realization of all or any part of the Collateral
pursuant hereto, and any other cash at the time held by the Collateral Agent
under Section 4 or this Section 5, shall be applied by the Collateral Agent:

First, to the payment of the reasonable costs and expenses of such collection,
sale or other realization, including reasonable out-of-pocket costs and expenses
of the Collateral Agent and the reasonable fees and expenses of its agents and
counsel, and all out -of-pocket expenses incurred and advances made by the
Collateral Agent in connection therewith;

Next, to the payment in full of the Secured Obligations, in each case equally
and ratably in accordance with the respective amounts thereof then due and owing
or as the Holders holding the same may otherwise agree; and

Finally, to the payment to the respective Grantors, or their respective
successors or assigns, or as a court of competent jurisdiction may direct, of
any surplus then remaining.

5.09.   Attorney-in-Fact. Without limiting any rights or powers granted by this
Agreement to the Collateral Agent while no Event of Default has occurred and is
continuing, the Collateral Agent is hereby appointed the attorney-in-fact of the
Grantors to, upon the occurrence and during the continuance of any Event of
Default, carry out the provisions of this Section 5 and take any action and
execute any instruments that the Collateral Agent may deem necessary or
advisable to accomplish the purposes hereof, which appointment as
attorney-in-fact is irrevocable and coupled with an interest; provided that,
Collateral Agent shall not execute on behalf of Grantors any application or
other instrument to be submitted to the FCC except to the extent permitted by
applicable law. Without limiting the generality of the foregoing, so long as the
Collateral Agent shall be entitled under this Section 5 to make collections in
respect of the Collateral, the Collateral Agent shall have the right and power
to receive, endorse and collect all checks made payable to the order of the
Grantors representing any dividend, payment or other distribution in respect of
the Collateral or any part thereof and to give full discharge for the same.

5.10.   Perfection and Recordation. Except as otherwise provided below, prior to
or concurrently with the execution and delivery of this Agreement, the Grantors
shall:

(a) file such financing statements in such offices as the Collateral Agent may
reasonably request to

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15

perfect the security interests granted by Section 3 of this Agreement (it being
understood that in no event shall financing statements be filed against fixtures
in the local jurisdictions of their location),

(b) deliver to the Collateral Agent all certificates evidencing any of the
Pledged Equity, accompanied by undated stock or other powers duly executed in
blank,

(c) deliver the originals of any of the promissory notes referred to in Section
3, accompanied by undated allonges or other powers duly executed in blank,

(d) cause each Share Issuer (other than an Share Issuer the ownership interests
in which are evidenced by certificates) that is a Subsidiary to agree that it
will comply with instructions regarding perfection and recordation originated by
the Collateral Agent, and

(e) execute, deliver and record such short form security agreements relating to
IP Collateral as the Collateral Agent may reasonably request and make such
filings, registrations and recordations thereof with the U.S. Patent and
Trademark Office and the U.S. Copyright Office, as applicable, as the Collateral
Agent may reasonably request.

Without limiting the foregoing, the Grantors consent that Uniform Commercial
Code financing statements may be filed describing the Collateral as “all assets”
or “all personal property” of the Grantors (provided that no such description
shall be deemed to modify the description of Collateral set forth in Section 3).

5.11.   Termination. Upon the payment of all Secured Obligations in full, this
Agreement shall terminate, and the Collateral Agent shall forthwith cause to be
assigned, transferred and delivered, against receipt but without any recourse,
warranty or representation whatsoever, any remaining Collateral and money
received in respect thereof, to or on the order of the respective Grantors and
to be released and canceled all licenses and rights referred to in Section
5.04(b) . The Collateral Agent shall also, at the expense of the Grantors,
execute and deliver to the respective Grantors upon such termination such
Uniform Commercial Code termination statements and such other documentation as
shall be reasonably requested by the respective Grantors to effect and evidence
the termination and release of the Liens on the Collateral.

5.12.   Release. To the extent that the Grantors are not prohibited by the terms
of the Indenture or this Agreement from selling, transferring or otherwise
assigning any of the Collateral hereunder, upon such sale, transfer or
assignment, such Collateral shall automatically be released from the Lien
created by this Agreement, and, upon the request of the Grantors in advance of
such sale, transfer or assignment, the Collateral Agent shall promptly assign,
transfer and deliver such Collateral to the Grantors. To the extent that any
Grantor is or shall be released from its obligations under the Financing
Documents pursuant to Section 4.07 of the Indenture, then the Collateral owned
by such Grantor (and all Equity Interests in such Grantor that constitute
Collateral) shall automatically be released from the Lien created by this
Agreement, and, upon the request of the applicable Grantor in advance of the
transaction or event pursuant to which such Grantor will be so released, the
Collateral Agent shall promptly assign, transfer and deliver all Collateral
owned by such Grantor to such Grantor. In addition, the Collateral Agent shall,
at the expense of the Grantors, execute and deliver to the appropriate Grantor
such Uniform Commercial Code termination statements or amendments to effect and
evidence the

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16

release of the Liens on such Collateral and execute any other evidence of such
Lien termination as may be requested by the Grantors.

5.13.   Further Assurances. Each Grantor agrees that, from time to time upon the
written request of the Collateral Agent, at the expense of such Grantor and,
subject to the terms hereof, such Grantor will promptly execute and use
commercially reasonable efforts to deliver, or otherwise authenticate, all
further instruments and documents, and take all further commercially reasonable
action that the Collateral Agent may reasonably request in order to perfect and
protect any pledge or security interest granted or purported to be granted by
such Grantor hereunder or to enable the Collateral Agent to exercise and enforce
its rights and remedies hereunder with respect to any Collateral of such Grantor
and do such other acts and things as the Collateral Agent may reasonably request
in order fully to effect the purposes of this Security Agreement, including,
without limitation, taking any other action contemplated by this Article 5. In
addition, each Grantor will furnish to the Collateral Agent from time to time
statements and schedules (or update any schedules and annexes hereto) further
identifying and describing the Collateral of such Grantor and such other reports
in connection with such Collateral as the Collateral Agent may reasonably
request, all in reasonable detail.

Section 6.      Miscellaneous.

6.01.   Notices. All notices, requests, consents and demands hereunder shall be
in writing and telecopied or delivered to the intended recipient at its “Address
for Notices” specified pursuant to Section 12.01 of the Indenture.

6.02.   No Waiver. No failure on the part of the Collateral Agent or any Holder
to exercise, and no course of dealing with respect to, and no delay in
exercising, any right, power or remedy hereunder shall operate as a waiver
thereof; nor shall any single or partial exercise by the Collateral Agent or any
Holder of any right, power or remedy hereunder preclude any other or further
exercise thereof or the exercise of any other right, power or remedy. The
remedies herein are cumulative and are not exclusive of any remedies provided by
law.

6.03.   Amendments, Etc.

(a) The terms of this Agreement may be waived, altered or amended only by an
instrument in writing duly executed by the Grantors and the Collateral Agent,
provided that any provision of this Agreement may be waived by the Collateral
Agent in a letter or agreement executed by the Collateral Agent or by facsimile
transmission from the Collateral Agent. Any such amendment or waiver shall be
binding upon the Collateral Agent and each Holder, each holder of any of the
Secured Obligations and the Grantors.

(b) Upon the execution and delivery by any Person of a security agreement
supplement in substantially the form of Exhibit A hereto, such Person shall be
and become a Grantor hereunder, and each reference in this Security Agreement
and the other Financing Documents to “Grantor” shall also mean and be a
reference to such Person, each reference in this Security Agreement and the
other Financing Documents to the “Collateral” shall also mean and be a reference
to the Collateral granted by such Person and each reference in this Security
Agreement to an Annex shall also mean and be a reference to the annexes attached
to such security agreement supplement.

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6.04.   Expenses. The Grantors jointly and severally agree to reimburse each of
the Holders and the Collateral Agent for all reasonable out-of-pocket costs and
expenses of the Holders and the Collateral Agent (including, without limitation,
the reasonable fees and expenses of one legal counsel) in connection with (i)
the administration of this Security Agreement and custody, preservation, use or
operation of, or the sale of, collection from or other realization upon, any of
the Collateral of any Grantor, (ii) any Event of Default and any enforcement or
collection proceeding resulting therefrom, including, without limitation, all
manner of participation in or other involvement with (w) performance by the
Collateral Agent of any obligations of the Grantors in respect of the Collateral
that the Grantors have failed or refused to perform, (x) bankruptcy, insolvency,
receivership, foreclosure, winding up or liquidation proceedings, or any actual
or attempted sale, or any exchange, enforcement, collection, compromise or
settlement in respect of any of the Collateral, and for the care of the
Collateral and defending or asserting rights and claims of the Collateral Agent
in respect thereof, by litigation or otherwise, including expenses of insurance,
(y) judicial or regulatory proceedings and (z) workout, restructuring or other
negotiations or proceedings (whether or not the workout, restructuring or
transaction contemplated thereby is consummated) and (iii) the enforcement of
this Section 6.04, and all such costs and expenses shall be Secured Obligations
entitled to the benefits of the collateral security provided pursuant to Section
3.

6.05.   Successors and Assigns. This Agreement shall be binding upon and inure
to the benefit of the respective successors and assigns of the Grantors, the
Collateral Agent, the Holders and each holder of any of the Secured Obligations
(provided that no Grantor shall assign or transfer its rights or obligations
hereunder without the prior written consent of the Collateral Agent).

6.06.   Counterparts. This Agreement may be executed in any number of
counterparts, all of which taken together shall constitute one and the same
instrument and any of the parties hereto may execute this Agreement by signing
any such counterpart.

6.07.   Governing Law. This Agreement shall be governed by, and construed in
accordance with, the law of the State of New York.

6.08.   Captions. The captions and section headings appearing herein are
included solely for convenience of reference and are not intended to affect the
interpretation of any provision of this Agreement.

6.09.   Certain Regulatory Requirements.

(a) Cooperation by Grantors. At any time after the occurrence and during the
continuance of an Event of Default, each Grantor shall take all lawful action
that the Collateral Agent may reasonably request in the exercise of its rights
and remedies hereunder, which include the right to require such Grantor to
transfer or assign any FCC License Rights, held by it or any of its Subsidiaries
to any party or parties to facilitate an arms’-length public or private sale for
the benefit of the Collateral Agent. In furtherance of this right, the Grantors
shall (i) cooperate fully with the Collateral Agent in obtaining all approvals
and consents from the FCC and each other Governmental Authority and from any
third parties that the Collateral Agent may deem necessary or advisable to
accomplish any such transfer or assignment, and (ii) prepare, execute and file
with the FCC and any other Governmental Authority any application, request for
consent, certificate or instrument that the

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18

 Collateral Agent may deem necessary or advisable to accomplish any such
transfer or assignment. If the Grantors fail to execute such applications,
requests for consent, certificates or instruments, the clerk of any court that
has jurisdiction over the Financing Documents may, upon an ex parte request by
the Collateral Agent, execute and file the same on behalf of the Grantors for
purposes of placing such request before the FCC, except to the extent as would
not be permissible under applicable law.

(b) Actions by Collateral Agent. To enforce the provisions of Section 5.05, the
Collateral Agent is authorized to request the consent or approval of the FCC or
any other Governmental Authority to a voluntary or an involuntary transfer of
control of the Grantors or the voluntary or involuntary assignment of any FCC
License Rights held by the Grantors. In connection with the exercise of its
remedies under this Agreement, the Collateral Agent may obtain the appointment
of a trustee or receiver to assume control of the Grantors, subject to any
required prior approval of the FCC or any other Governmental Authority. Such
trustee or receiver shall have all rights and powers provided to it by law or by
court order or provided to the Collateral Agent under this Agreement.

(c) Certain Limitations Upon Actions by Collateral Agent. Notwithstanding
anything to the contrary contained in this Agreement,

(i) the Collateral Agent will not take any action hereunder that would
constitute or result in any transfer of control or assignment of the FCC
Licenses without obtaining all necessary FCC and other Governmental Authority
approvals, and all voting rights in any Collateral representing control rights
in the holders of any FCC License shall remain with the Grantors notwithstanding
the occurrence of any Event of Default until such required consents of the FCC
shall have been obtained (and, in that connection, the Collateral Agent and the
Holders shall be entitled to rely on the advice of FCC counsel selected by the
Collateral Agent to determine whether FCC approval or other Governmental
Authority approvals are required), and

(ii) the Collateral Agent shall not foreclose on, sell, assign, transfer or
otherwise dispose of, or exercise any right to control the FCC Licenses as
provided herein or take any other action that would affect the operational,
voting, or other control of the Grantors, unless such action is taken in
accordance with the provisions of the Communications Act of 1934, as from time
to time amended, and the rules, regulations and policies of the FCC and any
other Governmental Authority.

(d) Acknowledgement by Grantors. Each Grantor acknowledges that the approval of
the FCC and each other appropriate Governmental Authority to the assignment of
the FCC License Rights is integral to the Collateral Agent’s realization of the
value of the Collateral, including, without limitation, the FCC Licenses, that
there is no adequate remedy at law for failure by the Grantor to comply with the
provisions of this Section 6.09 and that such failure could not be adequately
compensable in damages. Therefore, the Grantors agree that the provisions of
this Section 6.09 may be specifically enforced, without any requirement to post
bond (such rights being fully waived by Grantors) and without regard to the
adequacy of any remedies available at law (the defense of the adequacy of
remedies at law being fully waived by the Grantors).

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19

6.10.   Agents and Attorneys-in-Fact. The Collateral Agent may employ agents and
attorneys-in-fact in connection herewith and shall not be responsible for the
negligence or misconduct of any such agents or attorneys-in-fact selected by it
in good faith.

6.11.   Severability. If any provision hereof is invalid and unenforceable in
any jurisdiction, then, to the fullest extent permitted by law, (a) the other
provisions hereof shall remain in full force and effect in such jurisdiction and
(b) the invalidity or unenforceability of any provision hereof in any
jurisdiction shall not affect the validity or enforceability of such provision
in any other jurisdiction.

6.12.   No Senior Liens. Except as permitted under the Indenture, Grantors shall
not grant to any party any lien or security interest (other than Permitted
Liens) in any of the Collateral that is superior to the interest granted to the
Collateral Agent hereunder regardless of whether such security interest could be
held by, exercised by, or granted to Collateral Agent under applicable law. To
the extent that, by reason of changes in law or regulations or for any other
reason Grantors may grant to Collateral Agent additional rights with respect to
the FCC Licenses or rights facilitating Collateral Agent’s ability to foreclose
upon, acquire and/or dispose of such interests upon the occurrence of an Event
of Default, Grantors agree, upon notice from Collateral Agent, to amend this
agreement to provide such rights or such assurance to Collateral Agent.

[The remainder of this page has been intentionally left blank.]

 

 

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IN WITNESS WHEREOF, the parties hereto have caused this Security Agreement to be
duly executed and delivered as of the day and year first above written.

 

  MOTIENT CORPORATION     By: /s/ Neil L. Hazard    Name: Neil L. Hazard   
Title: Executive Vice President, Chief Financial Officer and Treasurer 

 

 

  MVH HOLDINGS INC.      By: /s/ Neil L. Hazard    Name: Neil L. Hazard   
Title: Vice President and Treasurer

 

 

  MOTIENT COMMUNICATIONS INC.      By: /s/ Neil L. Hazard    Name: Neil L.
Hazard    Title: Vice President and Treasurer

 

 

   MOTIENT LICENSE INC.      By: /s/ Neil L. Hazard    Name: Neil L. Hazard   
Title: Vice President and Treasurer

 

 

  MOTIENT SERVICES INC.      By: /s/ Neil L. Hazard    Name: Neil L. Hazard   
Title: Vice President and Treasurer

--------------------------------------------------------------------------------

 

  MOTIENT HOLDINGS INC.     By: /s/ Neil L. Hazard    Name: Neil L. Hazard   
Title: Vice President and Treasurer

 

 

  MOTIENT VENTURES HOLDING INC.     By: /s/ Neil L. Hazard    Name: Neil L.
Hazard    Title: Vice President and Treasurer

 

 

  TERRESTAR NETWORKS INC.     By: /s/ Neil L. Hazard    Name: Neil L. Hazard   
Title: Chief Financial Officer and Assistant
Secretary

 

--------------------------------------------------------------------------------

 

  U.S. BANK NATIONAL ASSOCIATION,   as Collateral Agent     By: /s/ Richard
Prokosch   Name: Richard Prokosch   Title: Vice President

 

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EXHIBIT A

FORM OF ADDITIONAL GRANTOR SUPPLEMENT

This ADDITIONAL GRANTOR SUPPLEMENT, dated  _________ ,  _____ (the “Additional
Grantor Supplement”), is delivered pursuant to the Security Agreement, dated as
of November 28, 2006 (as it may be from time to time amended, the “Security
Agreement”), among Motient Corporation, a Delaware corporation (“Motient”), each
of the other parties named therein as a grantor and any entities that may become
grantors in the future (the foregoing, collectively, the “Grantors”) in favor of
U.S. Bank, National Association, as the Collateral Agent (in such capacity,
together with its successors in such capacity, the “Collateral Agent”)..
Capitalized terms used herein not otherwise defined herein shall have the
meanings ascribed thereto in the Security Agreement.

Section 1. Grant of Security Interest. The undersigned (the “Additional
Grantor”) hereby grants to the Collateral Agent a security interest in and to
all of its right, title and interest in, to and under all property of the
undersigned that constitutes “Collateral” as defined in the Security Agreement.

Section 2. Security for Obligations. The grant of the security interest under
this Additional Grantor Supplement secures, and the Collateral is collateral
security for, the prompt and complete payment or performance in full when due,
whether at stated maturity, by required prepayment, declaration, acceleration,
demand or otherwise (including the payment of amounts that would become due but
for the operation of the automatic stay under Section 362(a) of the Bankruptcy
Code, 11 U.S.C. §362(a) (and any successor provision thereof)), of all Secured
Obligations of the Additional Grantor.

Section 3. Supplements to Security Agreement Annexes. The undersigned has
attached hereto supplemental Annexes ______________ to Annexes  _____________,
respectively, to the Security Agreement, and the undersigned hereby certifies,
as of the date first above written, that such supplemental schedules are
complete and correct in all material respects.

Section 4. Representations and Warrants and Covenants. The Additional Grantor
hereby makes each representation and warranty and covenant set forth in the
Security Agreement (as supplemented by the attached supplemental annexes) to the
same extent as each other Grantor.

Section 5. Obligations Under the Security Agreement. The undersigned hereby
agrees, as of the date first written above, to be bound as a Grantor by all of
the terms and provisions of the Security Agreement to the same extent as each of
the other Grantors. The undersigned further agrees, as of the date first written
above, that each reference in the Security Agreement to a “Grantor” shall also
mean and be a reference to the undersigned.

Section 6. Governing Law. This Additional Grantor Supplement shall be governed
by, and construed in accordance with, the law of the State of New York.

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IN WITNESS WHEREOF, the undersigned has caused this Additional Grantor
Supplement to be duly executed and delivered by its duly authorized officer as
of the date first written above.

[NAME OF ADDITIONAL GRANTOR]      By:_____________________________  Name: 
Title: