MOTIENT CORP
AETHER ESCROW AGREEMENT
<DOCUMENT>
<TYPE>EX-10.47
<SEQUENCE>18
<FILENAME>0018.txt
<DESCRIPTION>AETHER ESCROW AGREEMENT
<TEXT>

                                ESCROW AGREEMENT


     ESCROW AGREEMENT,  dated as of November 29, 2000 (the "Agreement"),  by and
among Motient  Services Inc., a Delaware  corporation  ("MSI"),  Aether Systems,
Inc., a Delaware  corporation  ("Aether"),  and SunTrust Bank,  acting as escrow
agent (the "Escrow Agent").

     WHEREAS,  Aether and MSI are parties to that certain  Asset Sale  Agreement
dated as of November  29, 2000 (the "Asset Sale  Agreement"),  pursuant to which
Aether has agreed to deposit Ten Million Dollars  ($10,000,000)  with the Escrow
Agent as payment  contingent upon the successful  Completion (as defined herein)
of MobileMAX2; and

     WHEREAS, MSI and Aether have agreed,  pursuant to the Asset Sale Agreement,
to enter into this Agreement.


     NOW  THEREFORE,  for good  and  valuable  consideration,  the  receipt  and
sufficiency  of which are hereby  acknowledged,  MSI,  Aether  and Escrow  Agent
(collectively, the "Parties") agree as follows:

1. Escrow Deposit.  Aether agrees to wire transfer on the Closing Date under the
Asset Sale  Agreement  the amount of Ten Million  Dollars  ($10,000,000)  to the
Escrow Agent for deposit as  hereinafter  provided (the "Escrow  Deposit").  The
Escrow Agent shall  acknowledge  receipt of the Escrow Deposit and hereby agrees
to accept the Escrow  Deposit  and  establish  and  maintain a separate  account
therefor as provided  herein.  The Escrow  Deposit as from time to time invested
and reinvested as herein provided  (including any interest or income of any kind
whatsoever thereon) is hereinafter referred to as the "Escrow Fund."

2.       Investment of the Escrow Fund.
         -----------------------------

2.1 Investment. The Escrow Agent shall invest any or all of the Escrow Fund, and
any undistributed  accretions thereto or income with respect thereto,  in any of
the following:

(a)  obligations  issued or  guaranteed  by the United  States of America or any
agency or instrumentality
thereof with a maturity of one year or less;

(b)  certificates  of deposit of or accounts with national banks or corporations
endowed with trust powers having capital and surplus in excess of $500,000,000;

(c)  commercial  paper at the time of  investment  of the Escrow Fund having the
highest  rating  available  from Standard & Poor's  Ratings  Services or Moody's
Investors Service, Inc.;

(d) fixed income  securities  with a maturity of one year or less of the highest
rating available from Standard & Poor's Ratings Services or by Moody's Investors
Service, Inc., or of a comparable quality;

(e) any mutual fund which  invests at least  eighty  percent  (80%) of its funds
primarily in one or more of the  obligations  described in paragraphs  (a), (b),
(c) or (d) above; or

(f) any other investment mutually agreed upon in writing by MSI and Aether.

     Such  investments  (other than those  referred to in  paragraph  (f) above)
shall be  executed  by the  Escrow  Agent  as  directed  in  writing  by  Aether
(provided, that investments pursuant to paragraph (f) above shall be made at the
joint direction of MSI and Aether);  provided,  that Aether shall not direct the
Escrow  Agent to  execute,  and the Escrow  Agent  shall not  execute,  any such
investment  which  cannot be  liquidated  without  penalty  for a period of time
exceeding  ten  (10)  days so as to  provide  for the  timely  availability  and
necessary liquidity of the Escrow Fund.

     In the  absence of written  instructions  pursuant  to Section  2.1 of this
Agreement,  the Escrow  Agent shall  invest the Escrow Fund in the money  market
funds  customarily  utilized by the Escrow Agent's corporate trust department in
the ordinary course of its corporate trust business in the usual  performance of
its escrow agent duties.

     The  Escrow  Agent  shall not be called  upon to advise any Party as to the
wisdom of selling or  retaining,  or taking or  refraining  from any action with
respect to, any securities or other property deposited hereunder.

     The  Escrow  Agent  does not have any  interest  in the  escrowed  property
deposited hereunder but is serving as escrow holder only, having only possession
thereof.  Any  payments  of income  from this  Escrow  Fund  shall be subject to
withholding regulations then in force with respect to United States taxes, which
shall  be  the   responsibility   of  Aether.   This  paragraph   shall  survive
notwithstanding  any  termination  of this  Agreement or the  resignation of the
Escrow Agent.

2.2  Escrow  Statements.  On or before  the tenth  (10th)  business  day of each
calendar  month  during  the term of this  Agreement  and  continuing  until the
termination of this  Agreement,  the Escrow Agent shall send to MSI and Aether a
statement  setting  forth all  interest or other income or other items added to,
all  interest or other  income on the Escrow Fund paid from,  and  distributions
from or other items charged against, the Escrow Fund for the preceding month.

2.3 Investment Income. Income, interest, increments and realized gains paid upon
the Escrow  Deposit  held in the Escrow Fund shall not become part of the Escrow
Deposit and shall instead be distributed to Aether on a monthly basis.

3.       Distributions from the Escrow Fund.
         ----------------------------------

3.1      Distributions.
         -------------

     (a) The Escrow  Deposit  shall be released to MSI promptly  upon the Escrow
Agent's  receipt of a joint written notice from MSI and Aether  instructing  the
Escrow Agent to disburse the Escrow Deposit in accordance with instructions from
MSI.

     (b) MSI may also request a distribution from the Escrow Fund by providing a
signed,  written notice (a "Distribution Notice") to the Escrow Agent, certified
by an officer of MSI,  stating that MSI has reasonable  grounds to believe that,
pursuant  to Section  2.3(a)(ii)  of the Asset  Sale  Agreement,  completion  of
MobileMAX2 has been deemed to occur ("Completion"). MSI agrees to provide Aether
no less than five (5) days' advance notice, via overnight courier, of its intent
to submit a Distribution  Notice to the Escrow Agent.  The  Distribution  Notice
shall also  include a statement  that MSI has provided  the  foregoing  required
notice to Aether.  When submitting the Distribution  Notice to the Escrow Agent,
MSI shall at the same time provide a copy of such notice to Aether.

     (c) If Aether does not deliver to the Escrow Agent a notice  contesting the
Completion  within fifteen (15) days of the  Distribution  Notice referred to in
(b) above, then the Escrow Agent shall,  within five (5) business days following
the  expiration of the 15-day  period,  distribute the Escrow Deposit to MSI, in
accordance with MSI's  instructions.  Upon such  distribution,  the Escrow Agent
shall  distribute  all  remaining  amounts in the Escrow Fund to Aether,  at the
address listed in Section 8.1.

3.2      Disputes.
         --------

     (a) If Aether  delivers a notice to the Escrow  Agent  pursuant  to Section
3.1(c), then the Escrow Agent shall retain the Escrow Deposit and shall disburse
the Escrow Deposit only upon receipt of joint written  instructions  to disburse
the Escrow Deposit executed by MSI and Aether, or the resolution of such dispute
pursuant to clause (b) below.

     (b) In the event that Aether disputes a Distribution Notice as set forth in
(a) above,  if MSI and  Aether  have not been able to resolve  the  dispute  and
submit joint written  instruction  to the Escrow Agent within sixty (60) days of
the  delivery  by Aether of notice of the  dispute,  then MSI and  Aether  shall
submit  the  dispute  to final  and  binding  arbitration  before  JAMS,  or its
successor,  pursuant to the United States  Arbitration  Act, 9 U.S.C.  Sec. 1 et
seq.  Either  party may  commence  the  arbitration  process  called for in this
Agreement by filing a written demand for  arbitration  with JAMS, with a copy to
the other  party.  The  arbitration  will be conducted  in  accordance  with the
provisions of JAMS' Comprehensive  Arbitration Rules and Procedures in effect at
the time of filing of the demand for arbitration. The arbitration tribunal shall
consist of one (1) arbitrator  appointed by mutual  agreement of MSI and Aether.
In the event of failure by the parties to agree on an  arbitrator  within thirty
(30) days, MSI and Aether shall each choose one (1) arbitrator approved by JAMS,
and such arbitrators shall jointly select a third  arbitrator.  The parties will
cooperate  with  JAMS  and  with  one  another  in  scheduling  the  arbitration
proceedings.  The parties covenant that they will participate in the arbitration
in good faith,  and that they will share equally in its costs. The provisions of
this Section 3.2 may be enforced by any court of competent jurisdiction, and the
party seeking  enforcement  shall be entitled to an award of all costs, fees and
expenses,  including  attorneys  fees,  to be paid  by the  party  against  whom
enforcement is ordered.  If the arbitration panel determines that there has been
a Completion of  MobileMAX2,  the Escrow Agent shall disburse the Escrow Deposit
promptly following receipt of notice thereof from the arbitration panel or JAMS.

     (c) In the event that a dispute is resolved in Aether's favor in accordance
with Sections  3.2(a) or (b) above,  and the Escrow  Deposit is not disbursed to
MSI, MSI may  subsequently  make a new request for a distribution  in accordance
with the procedures set forth in Section 3.1.

     (d) In the event that, prior to fourteen (14) months after the date of this
Agreement,  the Parties have not delivered a written notice  pursuant to Section
3.1(a),  and no  Distribution  Notice issued  pursuant to Section 3.1(b) remains
outstanding pending resolution of a dispute relating thereto pursuant to Section
3.2(b), then the Escrow Agent shall disburse the entire Escrow Fund to Aether at
the address listed in Section 8.1.

3.3 Termination Payment.  Within two (2) business days after the distribution of
the Escrow  Deposit to MSI,  the  Escrow  Agent  shall  distribute  the  amounts
remaining  in the Escrow  Fund,  including  any accrued  and unpaid  interest or
income on the Escrow Deposit, to Aether.

3.4 Joint  Instructions.  In addition to the  foregoing  procedures,  if MSI and
Aether jointly execute a written notice to the Escrow Agent providing the Escrow
Agent with  distribution  instructions  for all or a part of the Escrow Deposit,
the Escrow Agent shall distribute that portion of the Escrow Deposit referred to
in such notice in accordance with the instructions contained in such notice.

4.   Termination  of  Agreement.   This  Agreement   shall  terminate  upon  the
distribution  of the entire Escrow Fund pursuant to the  provisions of Section 3
of this Agreement.

5.       Duties of Escrow Agent.
         ----------------------

5.1 Duties  Limited.  The Escrow  Agent  shall not be under any duty to give the
Escrow Fund held by it  hereunder  any greater  degree of care than it gives its
own similar property and is reasonably expected of financial institutions acting
in similar capacities,  shall not be required to invest any funds held hereunder
except  as  directed  in this  Agreement,  and will be  regarded  as  making  no
representations  and having no  responsibilities  (except as expressly set forth
herein)  as to the  validity,  sufficiency,  value,  genuineness,  ownership  or
transfer of the Escrow Fund.  Uninvested  funds held hereunder shall not earn or
accrue  interest.  This  Agreement  expressly  sets  forth all the duties of the
Escrow Agent with respect to any and all matters  pertinent  hereto.  No implied
duties or  obligations  shall be read into this  Agreement  against  the  Escrow
Agent.  The Escrow Agent shall not be bound by the  provisions  of any agreement
among the other Parties except this Agreement.

     In the event of any  disagreement  between the other  Parties  resulting in
adverse  claims or demands being made in connection  with the Escrow Fund, or in
the event that the Escrow  Agent in good faith is in doubt as to what  action it
should take  hereunder,  the Escrow Agent shall retain the Escrow Fund until the
Escrow Agent shall have received (a) directions  from an arbitration  panel or a
court of competent  jurisdiction  directing delivery of the Escrow Fund or (b) a
written agreement executed by the other Parties directing delivery of the Escrow
Fund,  in which  event the  Escrow  Agent  shall  disburse  the  Escrow  Fund in
accordance with such directions or agreement.  The Escrow Agent shall act on the
directions of the arbitration panel or court order without further questions.

     The Escrow Agent shall not be obligated to take any legal action  hereunder
that might in its judgment  involve any expense or liability  unless it has been
furnished with reasonable indemnity.

     The Escrow  Agent may consult with counsel of its own choice and shall have
full and complete  authorization  and protection for any action taken or omitted
by it  hereunder  in good  faith  and in  accordance  with the  opinion  of such
counsel.

5.2  Reliance.  The  Escrow  Agent  shall be  entitled  to rely upon any  order,
judgment,  certification,  demand, notice, instrument or other writing delivered
to it hereunder  without  being  required to determine the  authenticity  or the
correctness  of any fact  stated  therein or the  propriety  or  validity or the
service  thereof.  The Escrow Agent may act in reliance  upon any  instrument or
signature believed by it to be genuine and may assume that any person purporting
to give  notice or  receipt  or  advice or make any  statement  or  execute  any
document in connection with the provisions hereof has been duly authorized to do
so.

5.3  Indemnification;  Good  Faith.  MSI and  Aether  each  agree,  jointly  and
severally,  to indemnify and hold harmless the Escrow Agent and its  controlling
persons,  directors,  officers,  agents and  employees  (each,  an  "Indemnified
Person"),  to the fullest extent  permitted by applicable  law, from and against
any losses, obligations,  damages,  liabilities,  penalties, actions, judgments,
suits,  costs,  expenses  or  disbursements  related to or  arising  out of this
Agreement or the Escrow Agent's role in connection herewith,  and will reimburse
each  Indemnified  Person  for  all  expenses  (including,  without  limitation,
reasonable counsel fees and  disbursements)  incurred by such Indemnified Person
in  connection  with  investigating,  preparing or defending  any such action or
claim in which any  Indemnified  Person  is a party.  MSI and  Aether  will not,
however,  be  responsible  for any losses,  obligations,  damages,  liabilities,
penalties,  actions,  judgments,  suits, costs,  expenses or disbursements which
result from the breach by the Escrow Agent of its obligations  hereunder,  which
breach was caused by gross negligence,  lack of good faith or willful misconduct
of any Indemnified  Person. No Indemnified Person shall be liable for any action
taken  or  omitted  to be  taken  by such  Indemnified  Person  hereunder  or in
connection  herewith in good faith and believed by such Indemnified Person to be
within the purview of this Agreement, except for its gross negligence or willful
misconduct.  In no event  shall any  Indemnified  Person be held  liable for any
special,  indirect or consequential  damages  resulting from any action taken or
omitted to be taken by it hereunder or in connection herewith even if advised of
the possibility of such damages. The foregoing indemnification shall survive any
termination  of this  Agreement  and the  resignation  or  removal of the Escrow
Agent.

     Without  limiting the  foregoing,  the Escrow Agent shall have the right to
liquidate any  investments  held,  in order to provide  funds  necessary to make
required  payments under this  Agreement.  The Escrow Agent,  in its capacity as
escrow  agent  hereunder,  shall have no liability  for any loss  sustained as a
result  of any  investments  made  pursuant  to the  instructions  of the  other
Parties,  as a result of any liquidation of any investment prior to its maturity
or for the failure of the other Parties to give the Escrow Agent instructions to
invest or reinvest the Escrow Fund or any earnings thereon. The Escrow Agent may
act pursuant to the advice of counsel (whether  regularly  retained or specially
employed) with respect to any matter relating to this Agreement and shall not be
liable for any action taken or omitted in accordance with such advice.

5.4 Taxpayer  Identification Number (TIN). Aether shall provide the Escrow Agent
with its  Taxpayer  Identification  Number  (TIN) as  assigned  by the  Internal
Revenue  Service.  All interest or income earned under this  Agreement  shall be
allocated and  distributed to Aether as described in this Agreement and reported
by Aether to the Internal Revenue Service as having been so allocated and paid.

6.       Resignation; Successor Escrow Agent.
         -----------------------------------

6.1  Resignation.  The Escrow Agent (and any successor  escrow agent) may at any
time resign as such by delivering the Escrow Fund to any successor  escrow agent
jointly  designated  by Aether and MSI in writing,  or to any court of competent
jurisdiction, whereupon the Escrow Agent shall be discharged of and from any and
all  further  obligations  arising  in  connection  with  this  Agreement.   The
resignation  of the  Escrow  Agent  will take  effect on the  earlier of (a) the
appointment of a successor  (including by a court of competent  jurisdiction) or
(b) the day which is thirty  (30) days after the date of delivery of its written
notice of  resignation  to Aether and MSI. If at that time the Escrow  Agent has
not received a designation of a successor  escrow agent, the Escrow Agent's sole
responsibility  after  that time  shall be to  safekeep  the  Escrow  Fund until
receipt  of  a  designation  of  successor  escrow  agent  or  a  joint  written
disposition  instruction  by the other  Parties  or a final  order of a court of
competent jurisdiction.

6.2  Termination.  MSI and Aether  together may terminate the appointment of the
Escrow  Agent  hereunder  upon  notice  specifying  the  date  upon  which  such
termination shall take effect. In the event of such termination,  MSI and Aether
shall within thirty (30) days of such notice jointly appoint a successor  escrow
agent and the Escrow  Agent shall turn over to such  successor  escrow agent all
funds in the  Escrow  Fund and any other  amounts  held by it  pursuant  to this
Agreement; provided, however, the Escrow Agent shall be entitled to withhold, in
full discharge thereof, an amount relating to its unpaid fees for which it shall
have  previously  submitted  an invoice to MSI and Aether.  Upon  receipt of the
funds and other amounts,  the successor escrow agent shall thereupon be bound by
all of the provisions hereof.

7. Escrow  Agent's Fees.  The Escrow Agent  compensation  for the services to be
rendered by the Escrow  Agent  hereunder,  along with all  reasonable  expenses,
disbursements  and  advances  incurred  or  made  by  the  Escrow  Agent  in the
performance of its duties  hereunder,  including  reasonable fees,  expenses and
disbursements of its counsel (collectively, the "Escrow Agent's Fees"), shall be
shared  equally by MSI and Aether,  and shall be paid within thirty (30) days of
receiving an itemized invoice from the Escrow Agent.

8.       Miscellaneous.
         -------------

8.1 Notices.  Any notice,  request,  instruction or other document deemed by the
Parties to be  necessary or desirable to be given to any other Party shall be in
writing and shall be deemed to have been given (i) upon  receipt if delivered in
person;  (ii) one day after deposit  prepaid with a national  overnight  express
service;  or (iii) three days after deposit in the United States certified mail,
postage  prepaid,  return  receipt  requested  (except  for the Escrow  Agent in
respect of whom any mailed  notice  shall be deemed  given when  received at the
address set forth below) to the following addresses:

         If to MSI:                         Motient Services Inc.
                                            10802 Parkridge Boulevard
                                            Reston, VA  20191
                                            Attention: Controller

         with a copy to:                    General Counsel


         If to Aether:                      Aether Systems, Inc.
                                            11460 Crownridge Drive
                                            Owings Mills, MD 21117
                                            Attention: General Counsel

         If to Escrow Agent:                SunTrust Bank
                                            919 East Main Street
                                            Richmond, VA 23219
                                            Attention: Escrow Administrator

The persons and  addresses set forth above may be changed from time to time by a
notice sent out as aforesaid.

8.2 Entire  Agreement.  This Agreement  contains the entire  agreement among the
Parties  with  respect to the subject  matter  hereof and  supersedes  all prior
agreements, written or oral.

8.3 Waivers and Amendments. This Agreement may be amended, superseded, canceled,
renewed or extended,  and the terms and conditions hereof may be waived, only by
a written instrument signed by the Parties,  or, in the case of a waiver, by the
Party waiving  compliance.  No delay on the part of any Party in exercising  any
right, power or privilege hereunder shall operate as a waiver thereof, nor shall
any waiver on the part of any Party of any such right,  power or privilege,  nor
any single or partial  exercise of any such right,  power or privilege  preclude
any further exercise  thereof or the exercise of any other such right,  power or
privilege.

8.4 Governing Law. This Agreement  shall be governed and construed in accordance
with the laws of the Commonwealth of Virginia without reference to its conflicts
of law doctrine.

8.5  Assignment.  No Party may assign  this  Agreement,  or any of its rights or
obligations hereunder, without the consent of the other Parties, which shall not
be unreasonably withheld.  This Agreement shall be binding upon and inure to the
benefit of the Parties and their respective permitted successors and assigns.

8.6 Further  Assurances.  Each of the Parties shall  execute such  documents and
other  papers and take such  further  actions as may be  reasonably  required or
desirable to carry out the provisions  hereof and the transactions  contemplated
hereby.

8.7 Variations in Pronouns. All pronouns and any variations thereof refer to the
masculine, feminine or neuter, singular or plural, as the context may require.

8.8  Counterparts.  This  Agreement  may be  executed by the Parties in separate
counterparts, each of which when so executed and delivered shall be an original,
but all such counterparts shall together constitute one and the same instrument.

8.9 Headings.  The headings in this  Agreement are for reference  only and shall
not affect the interpretation of this Agreement.

                       [SIGNATURES BEGIN ON THE NEXT PAGE]


<PAGE>




                  IN  WITNESS  WHEREOF,  the  Parties  have  caused  their  duly
authorized  representatives  to execute this Agreement  effective as of the date
first written above.


                                      MOTIENT SERVICES INC.


                                      By:/s/ Walter V. Purnell Jr.
                                         ---------------------------------------
                                      Name: Walter V. Purnell, Jr.
                                      Title:President & Chief Executive Officer


                                      AETHER SYSTEMS, INC.
                                      By:/s/ Brian W. Keane
                                         ---------------------------------------
                                      Name: Brian W. Keane
                                      Title:EVP


                                      SUNTRUST BANK

                                      By: /s/ Eric T. Rodriguez
                                         ---------------------------------------
                                      Name: Eric T. Rodriguez
                                      Title:Vice President



</TEXT>
</DOCUMENT>
