PLAN OF ARRANGEMENT
                       UNDER SECTION 192
            OF THE CANADA BUSINESS CORPORATIONS ACT


                           ARTICLE 1

                         INTERPRETATION

1.1  Definitions

           In  this Plan of Arrangement unless there is something
in  the  subject  matter or context inconsistent  therewith,  the
following terms shall have the respective meanings set out  below
and grammatical variations of such terms shall have corresponding
meanings:

      (a)   "Affiliate"  of  any person means  any  other  person
directly  or  indirectly  controlling, controlled  by,  or  under
common  control  with,  that person.  For the  purposes  of  this
definition, "control" (including, with correlative meanings,  the
terms  "controlling", "controlled by" and "under  common  control
with"), as applied to any person, means the possession by another
person,  directly or indirectly, of the power to direct or  cause
the  direction  of  the  management and policies  of  that  first
mentioned  person,  whether  through  the  ownership  of   voting
securities, by contract or otherwise;

      (b)  "Arrangement" means the arrangement under section  192
of the CBCA on the terms and subject to the conditions set out in
this  Plan of Arrangement, subject to any amendments thereto made
in  accordance with section 6.1 or made at the direction  of  the
Court in the Final Order;

      (c)  "Automatic Redemption Date" means November     , 2000,
unless  such date shall be accelerated at any time to a specified
earlier  date  by the Board of Directors upon at  least  75  days
prior  written  notice to the registered holders of  Exchangeable
Shares, in which case the Automatic Redemption Date shall be such
earlier date; provided, however, that the Board of Directors  may
so  accelerate the Automatic Redemption Date only at such time as
there are outstanding fewer than 400,000 Exchangeable Shares held
by holders other than Orbital and its Affiliates;

     (d)  "Average Closing Price" means the average closing sales
price of Orbital Common Shares for the 20 trading days ending  on
the  date  four  trading  days prior to the  Effective  Date,  as
reported on NASDAQ;

      (e)   "Board of Directors" means the board of directors  of
the Corporation;

      (f)  "Business Day" means any day other than a Saturday,  a
Sunday or a day when banks are not open for business in either or
both  of  the  Commonwealth of Virginia, and  Vancouver,  British
Columbia;

      (g)   "Canadian Dollar Equivalent" means in respect  of  an
amount  expressed  in a foreign currency (the  "Foreign  Currency
Amount") at any date the product obtained by multiplying (a)  the
Foreign  Currency  Amount by (b) the noon spot exchange  rate  on
such date for such foreign currency expressed in Canadian dollars
as  reported  by  the Bank of Canada or, in the event  such  spot
exchange  rate is not available, such exchange rate on such  date
for such foreign currency expressed in Canadian dollars as may be
deemed  by  the  Board  of Directors to be appropriate  for  such
purpose;

      (h)   "Capital  Reorganization" has  the  meaning  ascribed
thereto in section 5.7;

      (i)  "CBCA" means the Canada Business Corporations Act,  as
amended from time to time;

      (j)  "Class B Preferred Shares" means the Class B Preferred
Shares   of   the  Corporation  having  the  rights,  privileges,
restrictions and conditions set out in Appendix A annexed hereto.

      (k)   "Combination Agreement" means the  agreement  by  and
among  Orbital, the Corporation and MDA, dated as of  August  31,
1995,  as  the  same may be amended and restated, providing  for,
among other things, the Arrangement;

      (l)  "Corporation" means 3173623 Canada Inc., a corporation
existing under the CBCA;

     (m)  "Court" means the Supreme Court of British Columbia;

      (n)  "Current Market Price" means, in respect of an Orbital
Common  Share on any date, the Canadian Dollar Equivalent of  the
closing  sale price of Orbital Common Shares on such day (or,  if
no  trades of Orbital Common Shares occurred on such day, on  the
last  trading  day  prior thereto on which such trades  occurred)
reported on NASDAQ, or, if the Orbital Common Shares are not then
quoted  on  NASDAQ,  on  such other stock exchange  or  automated
quotation system on which the Orbital Common Shares are listed or
quoted,  as the case may be, as may be selected by the  Board  of
Directors  for such purpose; provided, however, that  if  in  the
opinion  of  the  Board of Directors the public  distribution  or
trading activity of Orbital Common Shares during such period does
not  create  a market that reflects the fair market value  of  an
Orbital Common Share, then the Current Market Price of an Orbital
Common Share shall be determined by the Board of Directors  based
upon  the advice of such qualified independent financial advisors
as  the  Board  of  Directors may deem  to  be  appropriate,  and
provided   further   that   any  such   selection,   opinion   or
determination  by the Board of Directors shall be conclusive  and
binding;

     (o)  "Current Orbital Common Share Equivalent" means, on any
date,  the equivalent as at such date of one Orbital Common Share
as  at  the  Effective  Date, expressed to four  decimal  places,
determined  by  applying  on  a cumulative  basis  the  following
adjustments,   to  the  extent  applicable  by  reason   of   any
transactions  occurring  in  respect  of  Orbital  Common  Shares
between  the  Effective Date and such date, the  Current  Orbital
Common Share Equivalent as at the Effective Date being 1.0000:

                           (i)         if   Orbital   shall   (A)
               subdivide, redivide or change its then outstanding
               Orbital  Common  Shares into a greater  number  of
               Orbital  Common Shares, unless the Corporation  is
               permitted under applicable law without a  vote  of
               its shareholders to make, and shall simultaneously
               make,  the  same  or  an  economically  equivalent
               change   to   the   rights  of  the   holders   of
               Exchangeable   Shares,   (B)   reduce,    combine,
               consolidate or change its then outstanding Orbital
               Common  Shares  into a lesser  number  of  Orbital
               Common Shares, unless the Corporation is permitted
               under  applicable  law  without  a  vote  of   its
               shareholders  to  make, and  shall  simultaneously
               make,  the  same  or  an  economically  equivalent
               change   to   the   rights  of  the   holders   of
               Exchangeable  Shares, or (C) issue Orbital  Common
               Shares  (or securities exchangeable or convertible
               into Orbital Common Shares) to the holders of  all
               or  substantially  all  of  its  then  outstanding
               Orbital Common Shares by way of stock dividend  or
               other  distribution  (other  than  to  holders  of
               Orbital  Common Shares who exercise an  option  to
               receive stock dividends in lieu of receiving  cash
               dividends),  unless the Corporation  is  permitted
               under  applicable  law  without  a  vote  of   its
               shareholders  to  issue or distribute,  and  shall
               simultaneously  issue  and distribute,  equivalent
               numbers   of  Orbital  Common  Shares   or   other
               securities  (adjusted if necessary  in  accordance
               with the Current Orbital Common Share Equivalent),
               or  the  economic equivalent on a per share basis,
               to  the holders of the Exchangeable Shares (any of
               such events being herein called an "Orbital Common
               Share Reorganization"), the Current Orbital Common
               Share   Equivalent  shall  be  adjusted  effective
               immediately  after the record date  at  which  the
               holders  of  Orbital Common Shares are  determined
               for  the  purpose  of  the  Orbital  Common  Share
               Reorganization by multiplying the Current  Orbital
               Common  Share Equivalent in effect on such  record
               date by the quotient obtained when:

                                    (I)   the  number of  Orbital
                    Common    Shares   outstanding   after    the
                    completion  of  such  Orbital  Common   Share
                    Reorganization (but before giving  effect  to
                    the issue of any Orbital Common Shares issued
                    after such record date otherwise than as part
                    of  such Orbital Common Share Reorganization)
                    including,   in  the  case  where  securities
                    exchangeable  or  convertible  into   Orbital
                    Common Shares are distributed, the number  of
                    Orbital  Common Shares that would  have  been
                    outstanding   had   such   securities    been
                    exchanged  for  or  converted  into   Orbital
                    Common Shares on such record date,

               is divided by

                                    (II)  the  number of  Orbital
                    Common Shares outstanding on such record date
                    before  giving  effect to the Orbital  Common
                    Share Reorganization;

                     (ii)            if at any time Orbital shall
               fix  a  record  date for the issuance  of  rights,
               options  or  warrants to the  holders  of  all  or
               substantially  all  of the Orbital  Common  Shares
               entitling  them  to subscribe for or  to  purchase
               Orbital  Common Shares (or securities  of  Orbital
               convertible into Orbital Common Shares) at a price
               per  Orbital Common Share (or having a  conversion
               price  per Orbital Common Share) of less than  the
               Pre-Dilution  Market Price on  such  record  date,
               unless   the   Corporation  is   permitted   under
               applicable  law without a vote of its shareholders
               to   issue,   and   shall  simultaneously   issue,
               equivalent  numbers  of such  rights,  options  or
               warrants, adjusted if necessary in accordance with
               the  Current  Orbital Common Share  Equivalent  at
               such  record  date,  or  the  economic  equivalent
               thereof  on  a per share basis, to the holders  of
               Exchangeable  Shares (any such event being  herein
               referred  to  as  a "Rights Offering"),  then  the
               Current  Orbital Common Share Equivalent  then  in
               effect  shall be adjusted immediately  after  such
               record  date  by  multiplying the Current  Orbital
               Common  Share Equivalent in effect on such  record
               date by the quotient obtained when:

                                          (A)   the  sum  of  the
                    number  of  Orbital Common Shares outstanding
                    on   such  record  date  and  the  number  of
                    additional Orbital Common Shares offered  for
                    subscription  or  purchase under  the  Rights
                    Offering  (or  the number of  Orbital  Common
                    Shares  into which the securities so  offered
                    are convertible)

             is divided by

                                          (B)   the  sum  of  the
                    number  of  Orbital Common Shares outstanding
                    on such record date and the number determined
                    by  dividing the aggregate price of the total
                    number  of  additional Orbital Common  Shares
                    offered  for  subscription or purchase  under
                    the   Rights   Offering  (or  the   aggregate
                    conversion    price   of   the    convertible
                    securities  so  offered) by the  Pre-Dilution
                    Market Price on such record date.

          Any  Orbital  Common Share owned by  or  held  for  the
          account   of  Orbital  shall  be  deemed  not   to   be
          outstanding  for  the purpose of any such  computation.
          If  such rights, options or warrants are not so  issued
          or  if, at the date of expiry of the rights, options or
          warrants subject to the Rights Offering, less than  all
          the  rights,  options or warrants have been  exercised,
          then  the Current Orbital Common Share Equivalent shall
          be  readjusted effective immediately after the date  of
          expiry  to  the Current Orbital Common Share Equivalent
          which would have been in effect if such record date had
          not  been fixed or to the Current Orbital Common  Share
          Equivalent which would then be in effect on the date of
          expiry  if the only rights, options or warrants  issued
          had been those that were exercised, as the case may be;

                          (iii)     if Orbital shall fix a record
               date for the making of a distribution (including a
               distribution  by  way of stock  dividend)  to  the
               holders   of   all   or  substantially   all   its
               outstanding Orbital Common Shares of

                                        (A)  shares of Orbital of
                    any  class  other than Orbital Common  Shares
                    (or  shares  convertible into Orbital  Common
                    Shares referred to in (i) (C) above),

                                         (B)  rights, options  or
                    warrants (excluding a Rights Offering),

                                         (C)   evidences  of  its
                    indebtedness      (excluding     indebtedness
                    convertible   into  Orbital   Common   Shares
                    referred to in (i) (C) above) or

                                         (D)   any  other  assets
                    (other than any of the distributions referred
                    to  in (A), (B) or (C), dividends paid in the
                    ordinary  course or an Orbital  Common  Share
                    Reorganization)

                                                  unless      the
                    Corporation is permitted under applicable law
                    without   a  vote  of  its  shareholders   to
                    distribute,    and    shall    simultaneously
                    distribute,  the  same  number   of   shares,
                    rights,  options  or warrants,  evidences  of
                    indebtedness or other assets, as the case may
                    be,  adjusted if necessary in accordance with
                    the  Current Orbital Common Share  Equivalent
                    as  at  such  record date,  or  the  economic
                    equivalent thereof on a per share  basis,  to
                    the  holders of Exchangeable Shares (any such
                    event  being herein referred to as a "Special
                    Distribution") then, in each such  case,  the
                    Current Orbital Common Share Equivalent shall
                    be  adjusted effective immediately after  the
                    record  date at which the holders of  Orbital
                    Common Shares are determined for the purposes
                    of  the  Special Distribution by  multiplying
                    the  Current Orbital Common Share  Equivalent
                    in effect on such record date by the quotient
                    obtained when:

                                               (I)   the  product
                         obtained  when  the  number  of  Orbital
                         Common  Shares outstanding on the record
                         date  is  multiplied by the Pre-Dilution
                         Market Price on such date,

               is divided by

                                    (II)  the difference obtained
                    when  the amount by which the aggregate  fair
                    market  value (as determined by the Board  of
                    Directors,  which  determination   shall   be
                    conclusive)  of the shares, rights,  options,
                    warrants,   evidences  of   indebtedness   or
                    assets,  as  the case may be, distributed  in
                    the  Special  Distribution exceeds  the  fair
                    market  value (as determined by the Board  of
                    Directors,  which  determination   shall   be
                    conclusive)  of  the consideration,  if  any,
                    received  therefor by Orbital, is  subtracted
                    from the product obtained when the number  of
                    Orbital  Common  Shares  outstanding  on  the
                    record date is multiplied by the Pre-Dilution
                    Market Price on such date,

                                         provided  that  no  such
               adjustment  shall be made if the  result  of  such
               adjustment  would  be  to  decrease  the   Current
               Orbital   Common   Share  Equivalent   in   effect
               immediately before such record date.  Any  Orbital
               Common  Share owned by or held for the account  of
               Orbital shall be deemed not to be outstanding  for
               the   purpose  of  any  such  computation.    Such
               adjustment  shall  be  made successively  whenever
               such  a record date is fixed.  To the extent  that
               such  distribution  is not so  made,  the  Current
               Orbital   Common   Share   Equivalent   shall   be
               readjusted  effective immediately to  the  Current
               Orbital  Common Share Equivalent which would  then
               be  in  effect based upon such shares  or  rights,
               options  or  warrants or evidences of indebtedness
               or assets actually distributed;

      (p)   "Depositary"  means Montreal  Trust  Company  at  its
principal  offices  in Vancouver, British Columbia  and  Toronto,
Ontario;

       (q)   "Effective  Date"  means  the  date  shown  on   the
certificate of arrangement issued by the Director under the  CBCA
giving effect to the Arrangement;

      (r)   "Effective  Time" means 12:01 a.m. on  the  Effective
Date;

      (s)  "Exchange Ratio" is equal to U.S. $5.41 divided by the
Average Closing Price, provided that in no event shall it be less
than 0.2705 or greater than 0.3607;

      (t)   "Exchangeable  Share Provisions"  means  the  rights,
privileges,   restrictions  and  conditions  attaching   to   the
Exchangeable Shares, which are set forth in Appendix A hereto;

     (u)  "Exchangeable Shares" means the Exchangeable Non-Voting
Shares   of   the  Corporation  having  the  rights,  privileges,
restrictions  and conditions set forth in the Exchangeable  Share
Provisions;

      (v)   "Final  Order"  means the final order  of  the  Court
approving  the  Arrangement as such order may be amended  by  the
Court at any time prior to the Effective Time;

      (w)  "Lien" means any lien, pledge, adverse claim, security
interest, mortgage, claim, charge or encumbrance;

      (x)   "Liquidation  Call Purchase Price"  has  the  meaning
ascribed thereto in subsection 5.2(a);

      (y)   "Liquidation  Call Right" has  the  meaning  ascribed
thereto in subsection 5.2(a);

      (z)  "Liquidation Date" has the meaning ascribed thereto in
section 4.1 of the Exchangeable Share Provisions;

     (aa) "MDA" means MacDonald, Dettwiler and Associates Ltd., a
corporation existing under the CBCA;

      (bb)  "MDA  Common Shares" means the common shares  in  the
capital  of  MDA,  including  all  rights  associated  therewith,
including  without  limitation all rights  associated  with  such
common shares pursuant to the Shareholder Protection Rights  Plan
Agreement  dated as of August 27, 1992 between MDA  and  Montreal
Trust Company of Canada, as Rights Agent, as amended from time to
time;

      (cc) "MDA 1988 Options" has the meaning ascribed thereto in
subsection 2.1(l);

     (dd) "Meeting" means the Special Meeting of the shareholders
of MDA (voting together as one class) and the holders of MDA 1988
Options  (voting separately from the shareholders  of  MDA  as  a
second class) to be held to consider the Arrangement;

     (ee) "NASDAQ" means the NASDAQ National Market System;

      (ff)  "Options" means options, whether vested or  unvested,
granted by MDA prior to the Effective Date to purchase MDA Common
Shares  pursuant  to  the  1988 Key Employee  Share  Option  Plan
("KESOP  88"), the 1988 Employee Share Option Plan  ("ESOP  88"),
the  Key  Employee Share Option Plan and the Amended and Restated
Key Employee Share Option Plan;

       (gg)  "Orbital"  means  Orbital  Sciences  Corporation,  a
corporation existing under the laws of the State of Delaware;

      (hh) "Orbital Call Notice" has the meaning ascribed thereto
in subsection 5.1(b);

      (ii)  "Orbital Common Share Reorganization" has the meaning
ascribed thereto in subsection 1.1(o);

      (jj)  "Orbital Common Shares" means the common  stock,  par
value $.01 per share, of Orbital;

      (kk)  "Pre-Dilution Market Price" means, in respect  of  an
Orbital  Common Share on any date, the Canadian Dollar Equivalent
of  the  average of the closing sale prices as reported on NASDAQ
of  such  shares during a period of 20 consecutive  trading  days
ending  on the fourth trading day prior to such date, or, if  the
Orbital  Common  Shares are not then quoted on  NASDAQ,  on  such
other  stock exchange or automated quotation system on which  the
Orbital Common Shares are listed or quoted as may be selected  by
the  Board of Directors for such purpose; provided, however, that
if   in  the  opinion  of  the  Board  of  Directors  the  public
distribution or trading activity of Orbital Common Shares  during
such  period  does  not create a market that  reflects  the  fair
market  value  of an Orbital Common Share, then the  Pre-Dilution
Market  Price  of an Orbital Common Share shall be determined  by
the  Board  of Directors based upon the advice of such  qualified
independent financial advisors as the Board of Directors may deem
to  be appropriate, and provided further that any such selection,
opinion  or  determination by the Board  of  Directors  shall  be
conclusive and binding;

     (ll) "Qualifying Holdco" means a corporation that shall have
become  a party to this Plan of Arrangement prior to the date  of
the  Meeting  pursuant to subsection 6.1(b) hereof  and  that  is
listed in Appendix B;

      (mm)  "Redemption  Call  Purchase Price"  has  the  meaning
ascribed thereto in subsection 5.3(a);

      (nn)  "Redemption  Call  Right" has  the  meaning  ascribed
thereto in subsection 5.3(a);

      (oo) "Retracted Shares" has the meaning ascribed thereto in
section 5.1 of the Exchangeable Share Provisions;

      (pp)  "Retraction  Call  Purchase Price"  has  the  meaning
ascribed thereto in subsection 5.1(a);

      (qq)  "Retraction  Call  Right" has  the  meaning  ascribed
thereto in subsection 5.1(a);

      (rr) "Retraction Date" has the meaning ascribed thereto  in
section 5.2 of the Exchangeable Share Provisions;

      (ss)  "Retraction Request" has the meaning ascribed thereto
in section 5.1 of the Exchangeable Share Provisions;

      (tt)  "Revised  Exercise Price"  of  an  Option  means  the
exercise price of such Option in effect immediately prior to  the
Effective Time divided by the Exchange Ratio;

     (uu) "Transfer Agent" means Montreal Trust Company of Canada
or  such  other person as may from time to time be the  Registrar
and Transfer Agent for the Exchangeable Shares; and

      (vv) "Voting and Exchange Trust Agreement" means the Voting
and Exchange Trust Agreement between the Corporation, Orbital and
State  Street  Bank and Trust Company, made as of  the  Effective
Date.

1.2  Sections and Headings

           The division of this Plan of Arrangement into sections
and the insertion of headings are for reference purposes only and
shall  not affect the interpretation of this Plan of Arrangement.
Unless  otherwise  indicated,  any  reference  in  this  Plan  of
Arrangement  to a section or an Appendix refers to the  specified
section of or Appendix to this Plan of Arrangement.

1.3  Number, Gender and Persons

           In  this  Plan  of  Arrangement,  unless  the  context
otherwise  requires, words importing the singular number  include
the plural and vice versa, words importing any gender include all
genders   and   words  importing  persons  include   individuals,
corporations,  partnerships, associations, trusts, unincorporated
organizations,  governmental bodies and other legal  or  business
entities of any kind.

1.4       Withholding Tax

          All amounts required to be paid, deposited or delivered
under  this  Plan  of  Arrangement shall be  paid,  deposited  or
delivered  after deduction of any amount required  by  applicable
law  to  be  deducted  or  withheld on account  of  tax  and  the
deduction  of  such amounts and remittance to the applicable  tax
authorities   shall,   to  the  extent  thereof,   satisfy   such
requirement to pay, deposit or deliver hereunder.


                           ARTICLE 2

                          ARRANGEMENT

2.1  Arrangement

           At  the  Effective  Time on the  Effective  Date,  the
following  shall  occur  and shall be  deemed  to  occur  in  the
following order without any further act or formality:

          (a)   The  authorized share capital of the  Corporation
          shall  be  amended to authorize an unlimited number  of
          Exchangeable  Shares  and  10,000  Class  B   Preferred
          Shares;  as  a result of such amendment the Corporation
          shall  have three classes of authorized share  capital,
          namely,  an  unlimited  number  of  Common  Shares,  an
          unlimited  number  of Exchangeable  Shares  and  10,000
          Class  B  Preferred  Shares,  the  rights,  privileges,
          restrictions and conditions attaching to each of  which
          classes shall be as set out in Appendix A.

          (b)   The  Corporation  shall  issue  10,000  Class   B
          Preferred Shares to Canadian Imperial Bank of  Commerce
          in  partial consideration for services rendered to  the
          Corporation in connection with the Arrangement.

          (c)   The  Corporation shall add to its stated  capital
          account  in respect of the Class B Preferred Shares  an
          amount  in  respect  of the Class  B  Preferred  Shares
          issued pursuant to subsection 2.1(b) equal to $10,000.

          (d)  Schedule A and paragraphs 1 and 2 of Schedule B to
          the  Articles of the Corporation shall be  deleted  and
          the sentence "The annexed Schedule A is incorporated in
          this form." contained in paragraph 4 of the Articles of
          the  Corporation shall be deleted and replaced with the
          words "not applicable".

          (e)   All of the outstanding MDA Common Shares,  except
          MDA  Common Shares owned beneficially and of record  by
          the  Qualifying Holdcos and MDA Common Shares  held  by
          holders  who have exercised their rights of dissent  in
          accordance  with  section  3.1  hereof  and   who   are
          ultimately  entitled  to be paid fair  value  for  such
          shares  (hereinafter, "Dissenters") shall be  exchanged
          by  the  holders thereof for Exchangeable  Shares,  the
          number of which shall be the product of such number  of
          MDA  Common  Shares being exchanged  and  the  Exchange
          Ratio.   Each former holder of MDA Common Shares (other
          than  the  Qualifying  Holdcos  and  Dissenters)  shall
          receive   the  whole  number  of  Exchangeable   Shares
          resulting from the exchange of such holder's MDA Common
          Shares  for the consideration set out in the  foregoing
          sentence.   In lieu of fractional Exchangeable  Shares,
          each  holder of an MDA Common Share who otherwise would
          be  entitled  to receive a fraction of an  Exchangeable
          Share   on  the  exchange  shall  be  paid  an   amount
          determined as set forth in section 4.3 hereto.

          (f)  Upon the exchange referred to in subsection 2.1(e)
          above, each holder of exchanged MDA Common Shares shall
          cease  to be such a holder, shall have his name removed
          from  the register of holders of MDA Common Shares  and
          shall  become  a  holder of the number  of  fully  paid
          Exchangeable Shares to which he is entitled as a result
          of  such exchange and such holder's name shall be added
          to  the  register  of  holders of  Exchangeable  Shares
          accordingly.

          (g)   All  of  the outstanding shares of  each  of  the
          Qualifying  Holdcos shall be exchanged by  the  holders
          thereof  for Exchangeable Shares, the number  of  which
          shall be the product of the number of MDA Common Shares
          owned  beneficially  and of record by  each  respective
          Qualifying Holdco and the Exchange Ratio.  Each  former
          holder  of shares of a Qualifying Holdco shall  receive
          the  whole number of Exchangeable Shares resulting from
          the   exchange  of  all  such  holder's  shares  of   a
          Qualifying Holdco for the consideration set out in  the
          foregoing sentence.  In lieu of fractional Exchangeable
          Shares,  each  holder of shares of a Qualifying  Holdco
          who  otherwise would be entitled to receive a  fraction
          of  an Exchangeable Share on the exchange shall be paid
          an  amount  determined  as set  forth  in  section  4.3
          hereto.

          (h)  Upon the exchange referred to in subsection 2.1(g)
          above,  each  holder  of  exchanged  Qualifying  Holdco
          shares shall cease to be such a holder, shall have  his
          name removed from the register of holders of Qualifying
          Holdco  shares and shall become a holder of the  number
          of  fully  paid  Exchangeable Shares  to  which  he  is
          entitled as a result of such exchange and such holder's
          name  shall  be  added to the register  of  holders  of
          Exchangeable Shares accordingly.

          (i)   The  Corporation shall add to its stated  capital
          account  in  respect  of  Exchangeable  Shares   issued
          pursuant to subsections 2.1(e) and (g) an amount  equal
          to  the  aggregate fair market value of the MDA  Common
          Shares exchanged pursuant to subsection 2.1(e) and  the
          shares  of  Qualifying  Holdcos exchanged  pursuant  to
          subsection  2.1(g)  and  immediately  thereafter   such
          stated  capital shall be reduced to an amount equal  to
          the  aggregate  of (i) the cost, for  purposes  of  the
          Income  Tax  Act  (Canada), to the Corporation  of  the
          shares of the Qualifying Holdcos exchanged pursuant  to
          subsection  (g)  and,  (ii) the  paid-up  capital,  for
          purposes  of the Income Tax Act (Canada),  of  the  MDA
          Common Shares exchanged pursuant to subsection (e), all
          as   determined  by  the  Board  of  Directors  of  the
          Corporation.

          (j)   Each of the Qualifying Holdcos shall be dissolved
          into and its assets distributed to the Corporation  and
          for  the  purposes  of  such dissolution  each  of  the
          Qualifying Holdcos is authorized and directed  to  file
          articles  of  dissolution with the Director  under  the
          CBCA  at  such  time as the board of directors  of  the
          Corporation shall determine.  The Corporation, and each
          of  the  Qualifying Holdcos are authorized and directed
          to   create   and   deliver  all  such  documents   and
          instruments  as  may  be necessary  or  appropriate  to
          implement the dissolution.

          (k)   The name of each of the Qualifying Holdcos  shall
          be  removed from the register of holders of MDA  Common
          Shares  and the Corporation shall be registered as  the
          holder  of all of the issued and outstanding MDA Common
          Shares.

          (l)   Except for Options granted pursuant to the  KESOP
          88  or the ESOP 88 ("MDA 1988 Options") to holders  who
          have  exercised their rights of dissent  in  accordance
          with section 3.1 hereof and who are ultimately entitled
          to be paid fair value for the MDA Common Shares subject
          to such MDA 1988 Options, each outstanding Option shall
          become an option to purchase a number of Orbital Common
          Shares  equal  to the product (rounded to  the  nearest
          whole number) of the Exchange Ratio times the number of
          MDA Common Shares subject to such Option and having  an
          exercise price equal to the Revised Exercise Price  and
          having the same vesting, expiration and other terms  as
          in  effect  immediately prior to  the  Effective  Time,
          subject to subsection (m).

          (m)   The KESOP 88 and the ESOP 88 shall be amended  by
          deleting  the words in subsection 9.1 of the  KESOP  88
          and  the  words in subsection 8.1 of the  ESOP  88  and
          replacing each of them with the words following:

                "In  the  event  that  the  outstanding
          Shares  of the Company shall be changed  into
          or  exchanged  for a different number  or  of
          kind  of  securities of  the  Company  or  of
          another   corporation,  whether  through   an
          arrangement,  amalgamation or  other  similar
          statutory    procedure,    or     a     share
          capitalization,        sub-division        or
          consolidation,    then   there    shall    be
          substituted  for each Share  subject  to  any
          such  Option,  for each share authorized  for
          issuance  pursuant to the Plan  but  not  yet
          covered  by  an  Option and for  the  maximum
          number of Shares issuable under the Plan with
          respect  to any year, the number and kind  of
          securities into which each outstanding  Share
          shall  be  so changed or for which each  such
          Share shall be exchanged.

                In  the event that there shall  be  any
          change,  other  than  as  specified  in  this
          subsection,  in  the  number   or   kind   of
          outstanding Shares of the Company or  of  any
          securities into which such Shares shall  have
          been  changed or for which Shares shall  have
          been  exchanged, then an equitable adjustment
          shall be made in the number or kind of Shares
          or any such securities theretofore authorized
          for issuance pursuant to the Plan but not yet
          covered  by an Option, of the Shares  or  any
          such securities then subject to an Option  or
          Options,  and  the maximum of Shares  or  any
          such  securities issuable under the Plan with
          respect  to any year, such adjustment  to  be
          reasonably determined by the Directors and to
          be effective and binding for all purposes.

                In the case of any such substitution or
          adjustment   as   provided   for   in    this
          subsection, the Option price for  each  share
          option   agreement  for  each  Share  covered
          thereby   prior   to  such  substitution   or
          adjustment   will   be  proportionately   and
          appropriately  varied.  Such variation  shall
          generally   require  that   the   number   of
          securities  covered by the Option  after  the
          relevant  event  multiplied  by  the  revised
          Option price shall equal the number of shares
          covered  by the Option prior to the  relevant
          event   multiplied  by  the  original  Option
          price.    No   adjustment   or   substitution
          provided for in this subsection shall require
          the Company in any share option agreement  to
          issue   a  fractional  Share  and  the  total
          substitution  or adjustment with  respect  to
          each  share option agreement shall be limited
          accordingly."

          (n)   The  name of the Corporation shall be changed  to
          "MacDonald Dettwiler Holdings Inc."


                           ARTICLE 3

                       RIGHTS OF DISSENT

3.1  Rights of Dissent

          Holders of MDA Common Shares or of MDA 1988 Options may
exercise rights of dissent with respect to such MDA Common Shares
or the MDA Common Shares subject to such MDA 1988 Options, as the
case  may  be  ("Dissenters' Shares").  In order to dissent  with
respect  to  MDA  1988 Options, such MDA 1988  Options  shall  be
deemed to have been exercised for the purpose of exercising  such
dissent  rights and the exercise price under each such  MDA  1988
Option  shall  be deemed to be satisfied by set-off  against  the
fair  value  paid  for  the Dissenters' Shares  subject  thereto,
provided  that  if  the holder of any such  MDA  1988  Option  is
ultimately not entitled to be paid fair value for the Dissenters'
Shares subject thereto, such MDA 1988 Option shall be deemed  not
to  have  been exercised and shall become an option  to  purchase
Orbital Common Shares in accordance with subsection 2.1(l).   All
such rights of dissent shall be exercised pursuant to and in  the
manner set forth in section 190 of the CBCA and this section  3.1
(the "Dissent Procedures") in connection with the Arrangement and
holders who duly exercise such rights of dissent and who:

          (a)   are ultimately entitled to be paid fair value for
          their  Dissenters'  Shares  shall  be  deemed  to  have
          transferred  such  Dissenters'  Shares   to   MDA   for
          cancellation on the Effective Date; or

          (b)  are ultimately not entitled, for any reason, to be
          paid  fair value for their Dissenters' Shares shall  be
          deemed  to have participated in the Arrangement on  the
          same  basis as any non-dissenting holder of MDA  Common
          Shares  or  Options,  as the case  may  be,  and  shall
          receive Exchangeable Shares on the basis determined  in
          accordance  with subsection 2.1(e) or  options  on  the
          basis  provided in subsection 2.1(l), as the  case  may
          be.

In  no  case  shall MDA be required to recognize such holders  as
holders of MDA Common Shares or MDA 1988 Options, as the case may
be,  on  and  after  the Effective Date, and the  names  of  such
holders of MDA Common Shares or MDA 1988 Options, as the case may
be,  shall be deleted from the register of holders of MDA  Common
Shares  and all records of Options maintained by the Corporation,
respectively, on the Effective Date.


                           ARTICLE 4

               CERTIFICATES AND FRACTIONAL SHARES

4.1  Issuance of Certificates Representing Exchangeable Shares

            At   or  promptly  after  the  Effective  Time,   the
Corporation shall deposit with the Depositary, for the benefit of
the   holders   of  MDA  Common  Shares  exchanged  pursuant   to
subsection  2.1(e)  and the holders of shares of  the  Qualifying
Holdcos  exchanged  pursuant to subsection  2.1(g),  certificates
representing   the   Exchangeable  Shares  issued   pursuant   to
subsections 2.1(f) and (h).  Upon surrender to the Depositary for
cancellation  of  a certificate which immediately  prior  to  the
Effective   Time  represented  outstanding  MDA   Common   Shares
exchanged pursuant to subsection 2.1(e) or outstanding shares  of
Qualifying  Holdcos exchanged pursuant to subsection  2.1(g),  as
the   case  may  be,  together  with  such  other  documents  and
instruments as would have been required to effect the transfer of
the  shares  formerly represented by such certificate  under  the
CBCA  and  the  articles and by-laws of MDA or  of  the  relevant
Qualifying  Holdco,  as  the case may  be,  and  such  additional
documents  and  instruments  as  the  Depositary  may  reasonably
require,  the  holder  of such surrendered certificate  shall  be
entitled  to  receive in exchange therefor,  and  the  Depositary
shall  deliver  to  such holder, a certificate representing  that
number (rounded down to the nearest whole number) of Exchangeable
Shares which such holder has the right to receive (together  with
any  dividends or distributions with respect thereto pursuant  to
section  4.2  and  any  cash in lieu of  fractional  Exchangeable
Shares   pursuant  to  section  4.3),  and  the  certificate   so
surrendered  shall forthwith be cancelled.  In  the  event  of  a
transfer  of  ownership  of  MDA  Common  Shares  which  is   not
registered   in  the  transfer  records  of  MDA,  a  certificate
representing  the  proper number of Exchangeable  Shares  may  be
issued  to a transferee if the certificate representing such  MDA
Common Shares is presented to the Depositary, accompanied by  all
documents  required to evidence and effect such transfer.   Until
surrendered as contemplated by this section 4.1, each certificate
which   immediately  prior  to  the  Effective  Time  represented
outstanding MDA Common Shares or outstanding shares of Qualifying
Holdcos,   as   the  case  may  be,  that  were   purchased   for
consideration consisting of Exchangeable Shares shall  be  deemed
at  any time after the Effective Time to represent only the right
to  receive  upon such surrender (i) the certificate representing
Exchangeable Shares as contemplated by this section 4.1,  (ii)  a
cash  payment  in lieu of any fractional Exchangeable  Shares  as
contemplated   by  section  4.3  and  (iii)  any   dividends   or
distributions  with  a  record  date  after  the  Effective  Time
theretofore  paid or payable with respect to Exchangeable  Shares
as contemplated by section 4.2.

4.2  Distributions with Respect to Unsurrendered Certificates

           No  dividends or other distributions declared or  made
after the Effective Time with respect to Exchangeable Shares with
a  record  date  after the Effective Time shall be  paid  to  the
holder of any unsurrendered certificate which, immediately  prior
to  the Effective Time, represented outstanding MDA Common Shares
or  shares of Qualifying Holdcos that were exchanged pursuant  to
section  2.1,  and  no cash payment in lieu of fractional  shares
shall  be paid to any such holder pursuant to section 4.3, unless
and  until  such certificate shall be surrendered  in  accordance
with  section 4.1.  Subject to applicable law and to section 4.5,
at the time of such surrender of any such certificate (or, in the
case  of  clause  (iii) below, at the appropriate payment  date),
there  shall  be  paid to the record holder  of  the  certificate
representing  whole  Exchangeable Shares into  which  the  shares
represented  by  the  surrendered  certificate  were   exchanged,
without interest, (i) the amount of any cash payable in lieu of a
fractional  Exchangeable Share to which such holder  is  entitled
pursuant  to section 4.3, (ii) the amount of dividends  or  other
distributions  with  a  record  date  after  the  Effective  Time
theretofore paid with respect to such whole Exchangeable  Shares,
and  (iii) the amount of dividends or other distributions with  a
record date after the Effective Time but prior to surrender and a
payment date subsequent to surrender payable with respect to such
whole Exchangeable Shares.

4.3  No Fractional Shares

            No  certificates  or  scrip  representing  fractional
Exchangeable  Shares  shall  be issued  upon  the  surrender  for
exchange of certificates pursuant to section 4.1 and no dividend,
stock  split  or  other change in the capital  structure  of  the
Corporation shall relate to any such fractional security and such
fractional interests shall not entitle the owner thereof to  vote
or   to  exercise  any  rights  as  a  security  holder  of   the
Corporation.   In  lieu of any such fractional  securities,  each
person entitled to a fractional interest in an Exchangeable Share
will  receive  an  amount of cash (rounded to the  nearest  whole
cent),  without interest, equal to the Canadian Dollar Equivalent
as  of  the  Effective Date of the product of (i) such  fraction,
multiplied by (ii) the Average Closing Price.

4.4  Lost Certificates

           If  any  certificate  that immediately  prior  to  the
Effective  Time  represented outstanding MDA Common  Shares  that
were  exchanged pursuant to section 2.1 has been lost, stolen  or
destroyed,  upon the making of an affidavit of that fact  by  the
person claiming such certificate to be lost, stolen or destroyed,
the  Depositary will issue in exchange for such lost,  stolen  or
destroyed  certificate,  certificates  representing  Exchangeable
Shares  (and any dividends or distributions with respect  thereto
and  any  cash  pursuant to section 4.3) deliverable  in  respect
thereof  as  determined  in accordance with  section  2.1.   When
authorizing  such  payment in exchange for any  lost,  stolen  or
destroyed   certificate,   the  person   to   whom   certificates
representing  Exchangeable Shares are to be issued  shall,  as  a
condition  precedent  to  the  issuance  thereof,  give  a   bond
satisfactory to MDA or the Corporation, as the case  may  be,  in
such  sum  as  MDA  or  the Corporation may direct  or  otherwise
indemnify MDA or the Corporation in a manner satisfactory to  the
Corporation  and MDA against any claim that may be  made  against
MDA or the Corporation with respect to the certificate alleged to
have been lost, stolen or destroyed.

4.5  Extinguishment of Rights

          Any certificate that immediately prior to the Effective
Time  represented  outstanding MDA Common Shares  or  outstanding
shares  of  a  Qualifying Holdco that were purchased pursuant  to
section  2.1  and  not  deposited,  with  all  other  instruments
required by section 4.1, on or prior to the sixth anniversary  of
the  Effective Date shall cease to represent a claim or  interest
of  any  kind  or  nature as a shareholder of MDA,  the  relevant
Qualifying  Holdco  or  the  Corporation.   On  such  date,   the
Exchangeable Shares to which the former registered holder of  the
certificate referred to in the preceding sentence was  ultimately
entitled  shall  be  deemed  to  have  been  surrendered  to  the
Corporation   together  with  all  entitlements   to   dividends,
distributions  and  interests  thereon  held  for   such   former
registered holder for no consideration.


                           ARTICLE 5

    CERTAIN RIGHTS OF ORBITAL TO ACQUIRE EXCHANGEABLE SHARES

5.1  Orbital Retraction Call Right

       (a)    Orbital  shall  have  the  overriding  right   (the
"Retraction Call Right"), notwithstanding the proposed redemption
of  Retracted Shares by the Corporation on a Retraction Date,  to
purchase  from  the  holder  of  the  Retracted  Shares  on   the
Retraction  Date the Retracted Shares upon payment by Orbital  to
the holder of an amount per share equal to (a) the Current Market
Price  multiplied by the Current Orbital Common Share Equivalent,
in  each  case determined on the Retraction Date, which shall  be
satisfied  in full in respect of the Retracted Shares by  causing
to  be  delivered  to such holder such whole  number  of  Orbital
Common  Shares as is equal to the product obtained by multiplying
the  number  of  Retracted Shares by the Current  Orbital  Common
Share  Equivalent  (together  with  an  amount  in  lieu  of  any
fractional  Orbital Common Share resulting from such  calculation
payable  in accordance with section 5.5), plus (b) the  aggregate
of  all  dividends  declared and unpaid on such  Retracted  Share
(collectively  the  "Retraction Call Purchase  Price").   In  the
event  of  the exercise of the Retraction Call Right by  Orbital,
the holder of the Retracted Shares shall be obligated to sell  to
Orbital,  and  Orbital  shall  be  obligated  to  purchase,   the
Retracted  Shares on the Retraction Date upon payment by  Orbital
to  such  holder of the Retraction Call Purchase Price  for  each
Retracted Share.

     (b)  In order to exercise the Retraction Call Right, Orbital
must notify the Transfer Agent in writing of its determination to
do  so  (the  "Orbital Call Notice") prior to the expiry  of  the
third Business Day after the receipt by the Transfer Agent of the
Retraction  Request.  If Orbital does not so notify the  Transfer
Agent,  the  Transfer Agent will notify the  holder  as  soon  as
possible thereafter that Orbital will not exercise the Retraction
Call  Right.  If Orbital delivers the Orbital Call Notice  before
the end of such three Business Day period, the Retraction Request
shall  thereupon be considered only to be an offer by the  holder
to  sell  the Retracted Shares to Orbital in accordance with  the
Retraction Call Right.  In such event, the Corporation shall  not
redeem the Retracted Shares and Orbital shall purchase from  such
holder  and  such holder shall sell to Orbital on the  Retraction
Date  the Retracted Shares for the Retraction Call Purchase Price
for each Retracted Share.

      (c)   For  the  purposes of completing a  purchase  of  the
Retracted  Shares pursuant to the Retraction Call Right,  Orbital
shall  deposit  with  the  Transfer  Agent,  on  or  before   the
Retraction  Date,  certificates representing the  Orbital  Common
Shares  to be delivered to the holder of the Retracted Shares  in
payment  of  the  total Retraction Call Purchase  Price  for  the
Retracted  Shares  (or  the portion thereof  payable  in  Orbital
Common Shares, as the case may be) and a cheque in the amount  of
the  remaining  portion,  if any, of the  total  Retraction  Call
Purchase  Price (or, if any part of the Retraction Call  Purchase
Price consists of dividends payable in property, such property or
property that is the same as or economically equivalent  to  such
property).   Provided  that such total Retraction  Call  Purchase
Price  has been so deposited with the Transfer Agent, the closing
of  the purchase and sale of the Retracted Shares pursuant to the
Retraction Call Right shall be deemed to have occurred as of  the
close  of  business  on  the Retraction  Date  and,  for  greater
certainty,  no  redemption by the Corporation of  such  Retracted
Shares  shall  take place on the Retraction Date.  Orbital  shall
cause  the  Transfer  Agent  to deliver  to  the  holder  of  the
Retracted Shares, at the address of such holder recorded  in  the
securities  register  of  the Corporation  for  the  Exchangeable
Shares  or  at  the address specified in the holder's  Retraction
Request or by holding for pick-up by the holder at the office  of
the Transfer Agent to which the Retraction Request was delivered,
in   payment  of  such  total  Retraction  Call  Purchase  Price,
certificates  representing  the  Orbital  Common  Shares  to   be
delivered in respect of such payment (which shares shall be  duly
issued  as  fully paid and non-assessable and shall be  free  and
clear  of any Liens) registered in the name of the holder  or  in
such other name as the holder may request in payment of such and,
if applicable, a cheque of Orbital payable at par and in Canadian
dollars  at  any  branch  of  the  bankers  of  Orbital  or   the
Corporation  in  Canada (or, if any part of the  Retraction  Call
Purchase  Price  consists of dividends payable in property,  such
property  or  property  that  is  the  same  as  or  economically
equivalent  to  such  property),  and  such  delivery   of   such
certificates and cheque (and property, if any) to the  holder  on
behalf  of  Orbital by the Transfer Agent shall be deemed  to  be
payment of and shall satisfy and discharge all liability for  the
total Retraction Call Purchase Price to the extent that the  same
is  represented  by  such  share  certificates  and  cheque  (and
property,  if  any),  unless  such cheque  is  not  paid  on  due
presentation.   On  and  after  the  close  of  business  on  the
Retraction  Date, the holder of the Retracted Shares shall  cease
to be a holder of such Retracted Shares and shall not be entitled
to  exercise  any  of the rights of a holder in respect  thereof,
other  than  the  right to receive the Retraction  Call  Purchase
Price, unless upon presentation and surrender of certificates  in
accordance  with the foregoing provisions, payment of  the  total
Retraction  Call Purchase Price shall not be made, in which  case
the rights of such holder shall remain unaffected until the total
Retraction  Call  Purchase Price has  been  paid  in  the  manner
hereinbefore provided.  On and after the close of business on the
Retraction  Date,  provided that presentation  and  surrender  of
certificates  and payment of the total Retraction  Call  Purchase
Price  has been made in accordance with the foregoing provisions,
the  holder of the Retracted Shares so purchased by Orbital shall
thereafter  be  considered and deemed for all purposes  to  be  a
holder of the Orbital Common Shares delivered to such holder.

5.2  Orbital Liquidation Call Right

       (a)    Orbital  shall  have  the  overriding  right   (the
"Liquidation  Call  Right"), in the event of and  notwithstanding
the  proposed  liquidation,  dissolution  or  winding-up  of  the
Corporation, to purchase from all but not less than  all  of  the
holders  (other than Orbital and its Affiliates) of  Exchangeable
Shares  on the Liquidation Date all but not less than all of  the
Exchangeable  Shares  held  by each such  holder  on  payment  by
Orbital  of  an amount per share equal to (a) the Current  Market
Price  multiplied by the Current Orbital Common Share Equivalent,
in  each case determined on the Liquidation Date, which shall  be
satisfied  in  full in respect of all of the Exchangeable  Shares
held  by  such holder by Orbital causing to be delivered to  such
holder such whole number of Orbital Common Shares as is equal  to
the   product  obtained  by  multiplying  the  number   of   such
Exchangeable   Shares  by  the  Current  Orbital   Common   Share
Equivalent  (together with an amount in lieu  of  any  fractional
Orbital  Common Share resulting from such calculation payable  in
accordance  with  section 5.5), plus (b)  the  aggregate  of  all
dividends  declared and unpaid on such Exchangeable Share  up  to
the Liquidation Date (collectively the "Liquidation Call Purchase
Price").   In  the event of the exercise of the Liquidation  Call
Right by Orbital, each holder shall be obligated to sell all  the
Exchangeable  Shares  held  by  the  holder  to  Orbital  on  the
Liquidation  Date  on payment by Orbital to  the  holder  of  the
Liquidation Call Purchase Price for each such share.

      (b)   To exercise the Liquidation Call Right, Orbital  must
notify  the  Transfer  Agent  and the  Corporation  of  Orbital's
intention  to  exercise such right at least 30  days  before  the
Liquidation   Date  in  the  case  of  a  voluntary  liquidation,
dissolution  or winding up of the Corporation and at  least  five
Business  Days  before the Liquidation Date in  the  case  of  an
involuntary  liquidation,  dissolution  or  winding  up  of   the
Corporation.   The  Transfer Agent will  notify  the  holders  of
Exchangeable  Shares as to whether or not Orbital  has  exercised
the Liquidation Call Right forthwith after the expiry of the date
by  which  the  same  may be exercised by  Orbital.   If  Orbital
exercises  the  Liquidation Call Right, on the  Liquidation  Date
Orbital  will  purchase and the holders  will  sell  all  of  the
Exchangeable Shares then outstanding for a price per share  equal
to the Liquidation Call Purchase Price.

      (c)   For  the purposes of completing the purchase  of  the
Exchangeable  Shares  pursuant to  the  Liquidation  Call  Right,
Orbital  shall deposit with the Transfer Agent, on or before  the
Liquidation Date, certificates representing the aggregate  number
of  Orbital  Common Shares deliverable by Orbital  (which  shares
shall  be duly issued as fully paid and non-assessable and  shall
be  free  and  clear  of  any Liens)  in  payment  of  the  total
Liquidation  Call Purchase Price (or the portion thereof  payable
in  Orbital  Common Shares, as the case may be) and a  cheque  or
cheques  in the amount of the remaining portion, if any,  of  the
total  Liquidation Call Purchase Price (or, if any  part  of  the
Liquidation Call Purchase Price consists of dividends payable  in
property,  such  property or property that  is  the  same  as  or
economically  equivalent to such property).  Provided  that  such
total Liquidation Call Purchase Price has been so deposited  with
the  Transfer Agent, on and after the Liquidation Date the rights
of  each  holder  of  Exchangeable  Shares  will  be  limited  to
receiving   such  holder's  proportionate  part  of   the   total
Liquidation   Call  Purchase  Price  payable  by   Orbital   upon
presentation   and  surrender  by  the  holder  of   certificates
representing the Exchangeable Shares held by such holder and  the
holder shall on and after the Liquidation Date be considered  and
deemed  for  all purposes to be the holder of the Orbital  Common
Shares delivered to it.  Upon surrender to the Transfer Agent  of
a  certificate or certificates representing Exchangeable  Shares,
together  with  such other documents and instruments  as  may  be
required  to effect a transfer of Exchangeable Shares  under  the
CBCA  and  the articles and by-laws of the Corporation  and  such
additional  documents and instruments as the Transfer  Agent  may
reasonably require, the holder of such surrendered certificate or
certificates  shall be entitled to receive in exchange  therefor,
and the Transfer Agent on behalf of Orbital shall deliver to such
holder,  certificates representing the Orbital Common  Shares  to
which  the holder is entitled and a cheque or cheques of  Orbital
payable  at  par  and in Canadian dollars at any  branch  of  the
bankers of Orbital or of the Corporation in Canada in payment  of
the  remaining  portion,  if any, of the total  Liquidation  Call
Purchase  Price (or, if any part of the Liquidation Call Purchase
Price consists of dividends payable in property, such property or
property that is the same as or economically equivalent  to  such
property).   If  Orbital does not exercise the  Liquidation  Call
Right in the manner described above, on the Liquidation Date  the
holders of the Exchangeable Shares will be entitled to receive in
exchange therefor the Liquidation Amount otherwise payable by the
Corporation  in  connection with the liquidation, dissolution  or
winding-up of the Corporation pursuant to sections 4.1 to 4.3  of
the Exchangeable Share Provisions.

5.3  Orbital Redemption Call Right

       (a)    Orbital  shall  have  the  overriding  right   (the
"Redemption Call Right"), notwithstanding the proposed redemption
of  the  Exchangeable Shares by the Corporation on the  Automatic
Redemption  Date, to purchase from all but not less than  all  of
the   holders   (other  than  Orbital  or  its   Affiliates)   of
Exchangeable Shares on the Automatic Redemption Date all but  not
less than all of the Exchangeable Shares held by each such holder
on  payment by Orbital to the holder of an amount per share equal
to (a) the Current Market Price multiplied by the Current Orbital
Common Share Equivalent, in each case determined on the Automatic
Redemption  Date, which shall be satisfied in full in respect  of
all of the Exchangeable Shares held by such holder by causing  to
be  delivered to such holder such number of Orbital Common Shares
as  is equal to the product obtained by multiplying the number of
such  Exchangeable  Shares by the Current  Orbital  Common  Share
Equivalent  (together with an amount in lieu  of  any  fractional
Orbital  Common Share resulting from such calculation payable  in
accordance  with  section 5.5), plus (b)  the  aggregate  of  all
dividends   declared  and  unpaid  on  such  Exchangeable   Share
(collectively  the  "Redemption Call Purchase  Price").   In  the
event  of  the exercise of the Redemption Call Right by  Orbital,
each  holder  shall be obligated to sell to Orbital, and  Orbital
shall be obligated to purchase, all the Exchangeable Shares  held
by  the  holder  on the Automatic Redemption Date on  payment  by
Orbital  to the holder of the Redemption Call Purchase Price  for
each such share.

      (b)   To  exercise the Redemption Call Right, Orbital  must
notify  the  Transfer  Agent, as agent for  the  holders  of  the
Exchangeable  Shares, and the Corporation of Orbital's  intention
to  exercise  such  right at least 75 days before  the  Automatic
Redemption  Date.  The Transfer Agent will notify the holders  of
the  Exchangeable  Shares  as  to  whether  or  not  Orbital  has
exercised the Redemption Call Right forthwith after the  date  by
which the same may be exercised by Orbital.  If Orbital exercises
the  Redemption  Call  Right, on the  Automatic  Redemption  Date
Orbital  will  purchase and the holders  will  sell  all  of  the
Exchangeable Shares then outstanding for a price per share  equal
to the Redemption Call Purchase Price.

      (c)   For  the purposes of completing the purchase  of  the
Exchangeable  Shares  pursuant  to  the  Redemption  Call  Right,
Orbital  shall deposit with the Transfer Agent, on or before  the
Automatic   Redemption   Date,  certificates   representing   the
aggregate number of Orbital Common Shares deliverable by  Orbital
(which   shares   shall  be  duly  issued  as  fully   paid   and
non-assessable  and  shall be free and clear  of  any  Liens)  in
payment  of  the  total Redemption Call Purchase  Price  (or  the
portion thereof payable in Orbital Common Shares, as the case may
be)  and  a  cheque  or cheques in the amount  of  the  remaining
portion, if any, of the total Redemption Call Purchase Price (or,
if  part  of  the  Redemption  Call Purchase  Price  consists  of
dividends payable in property, such property or property the same
as  or economically equivalent to such property).  Provided  that
such  total Redemption Call Purchase Price has been so  deposited
with  the  Transfer Agent, on and after the Automatic  Redemption
Date  the  rights of each holder of Exchangeable Shares  will  be
limited  to  receiving such holder's proportionate  part  of  the
total  Redemption  Call Purchase Price payable  by  Orbital  upon
presentation   and  surrender  by  the  holder  of   certificates
representing the Exchangeable Shares held by such holder and  the
holder  shall  on  and  after the Automatic  Redemption  Date  be
considered  and deemed for all purposes to be the holder  of  the
Orbital  Common Shares delivered to such holder.  Upon  surrender
to   the   Transfer  Agent  of  a  certificate  or   certificates
representing  Exchangeable  Shares,  together  with  such   other
documents and instruments as may be required to effect a transfer
of  Exchangeable  Shares  under the CBCA  and  the  articles  and
by-laws  of  the  Corporation and such additional  documents  and
instruments  as  the Transfer Agent may reasonably  require,  the
holder  of such surrendered certificate or certificates shall  be
entitled to receive in exchange therefor, and the Transfer  Agent
on  behalf  of Orbital shall deliver to such holder, certificates
representing  the Orbital Common Shares to which  the  holder  is
entitled and a cheque or cheques of Orbital payable at par and in
Canadian  dollars at any branch of the bankers of Orbital  or  of
the Corporation in Canada in payment of the remaining portion, if
any, of the total Redemption Call Purchase Price (or, if part  of
the  Redemption Call Purchase Price consists of dividends payable
in   property,  such  property  or  property  the  same   as   or
economically equivalent to such property).  If Orbital  does  not
exercise the Redemption Call Right in the manner described above,
on  the Automatic Redemption Date the holders of the Exchangeable
Shares  will  be  entitled to receive in  exchange  therefor  the
redemption   price  otherwise  payable  by  the  Corporation   in
connection  with  the  redemption  of  the  Exchangeable   Shares
pursuant  to  sections  6.1  and 6.2 of  the  Exchangeable  Share
Provisions.

5.4  Consideration for Call Rights of Orbital

           The  Retraction Call Right, the Liquidation Call Right
and  the  Redemption Call Right are granted  to  Orbital  by  the
holders  of Exchangeable Shares in consideration of the grant  by
Orbital  of  the  Voting Rights, Automatic  Exchange  Rights  and
Exchange  Right  (as such terms are respectively defined  in  the
Voting  and Exchange Trust Agreement) to the Trustee (as  defined
in  the  Exchangeable Share Provisions) for the  benefit  of  the
holders of Exchangeable Shares.

5.5  Fractional Orbital Common Shares

            No  certificates  or  scrip  representing  fractional
Orbital   Common  Shares  shall  be  delivered  to   holders   of
Exchangeable Shares pursuant to the provisions hereof.   In  lieu
of  any  such  fractional security, each  person  entitled  to  a
fractional  interest in an Orbital Common Share will  receive  an
amount  of  cash  (rounded to the nearest  whole  cent),  without
interest,  equal  to  the Canadian Dollar Equivalent  as  of  the
fourth  Business Day prior to the relevant date  of  delivery  of
certificates representing Orbital Common Shares (the  "Fractional
Share  Calculation  Date") of the product of (i)  such  fraction,
multiplied  by  (ii)  the closing sale price  of  Orbital  Common
Shares  as reported on NASDAQ on the Fractional Share Calculation
Date.

5.6  Economic Equivalence

           The  Board of Directors shall determine, in good faith
and in its sole discretion (with the assistance of such reputable
and qualified independent financial advisors and/or other experts
as  the Board of Directors may require) economic equivalence  for
the  purposes  of  any  provision herein  that  requires  such  a
determination and each such determination shall be conclusive and
binding on Orbital and the holders of Exchangeable Shares,  where
applicable.

5.7  Capital Reorganization of Orbital

           If  at  any time there is a capital reorganization  of
Orbital  that  is  not  provided for in subsection  1.1(o)  or  a
consolidation, merger, arrangement or amalgamation (statutory  or
otherwise) of Orbital with or into another entity (any such event
being   called  a  "Capital  Reorganization"),  any   holder   of
Exchangeable  Shares  whose Exchangeable  Shares  have  not  been
exchanged  for  Orbital  Common Shares  in  accordance  with  the
provisions  hereof  prior to the record  date  for  such  Capital
Reorganization  shall be entitled to receive  and  shall  accept,
upon  any  such  exchange occurring pursuant  to  the  provisions
hereof  at  any  time  after the record  date  for  such  Capital
Reorganization,  in  lieu of the Orbital Common  Shares  that  he
would  otherwise  have been entitled to receive pursuant  to  the
provisions  hereof, the number of shares or other  securities  of
Orbital  or  of  the  body  corporate  resulting,  surviving   or
continuing  from  the Capital Reorganization, or other  property,
that  such holder would have been entitled to receive as a result
of  such  Capital Reorganization if, on the record date,  he  had
been the registered holder of the number of Orbital Common Shares
to   which  he  was  then  entitled  upon  any  exchange  of  his
Exchangeable Shares into Orbital Common Shares in accordance with
the  provisions hereof, subject to adjustment thereafter  in  the
same manner, as nearly as may be possible, as is provided for  in
subsection  1.1(o); provided that no such Capital  Reorganization
shall  be  carried into effect unless all necessary  steps  shall
have  been taken so that each holder of Exchangeable Shares shall
thereafter  be  entitled to receive, upon  any  exchange  of  his
Exchangeable  Shares  pursuant to  the  provisions  hereof,  such
number  of shares or other securities of Orbital or of  the  body
corporate  resulting, surviving or continuing  from  the  Capital
Reorganization, or other property.

5.8  Other Change in Orbital Common Shares

          In the case of any reclassification of, or other change
in,  the  outstanding Orbital Common Shares other than  a  Common
Share  Reorganization or a Capital Reorganization,  such  changes
shall be made in the rights attaching to the Exchangeable Shares,
without  any action on the part of the Corporation or the holders
of  the Exchangeable Shares to the extent permitted by applicable
law,  effective immediately following the record  date  for  such
reclassification  or  other change, to the  extent  necessary  to
ensure  that holders of Exchangeable Shares shall be entitled  to
receive,  upon the occurrence at any time after such record  date
of  any  event  whereby they would receive Orbital Common  Shares
pursuant  to  the provisions hereof, such shares,  securities  or
rights  as they would have received if their Exchangeable  Shares
had  been  exchanged for Orbital Common Shares  pursuant  to  the
provisions hereof immediately prior to such record date,  subject
to  adjustment thereafter in the same manner, as nearly as may be
possible, as is provided for in subsection 1.1(o).


                           ARTICLE 6

                           AMENDMENT

6.1  Plan of Arrangement Amendment

      (a)   By instrument in writing the Corporation and MDA  may
amend,  modify and/or supplement this Plan of Arrangement at  any
time  and  from  time to time provided that any  such  amendment,
modification,  or supplement must be (i) agreed  to  by  Orbital,
(ii)  filed  with the Court and, if made following  the  Meeting,
approved  by the Court and (iii) communicated to holders  of  MDA
Common Shares and Options in the manner required by the Court (if
so required).

      (b)   Notwithstanding subsection 6.1(a), by  instrument  in
writing  the Corporation and MDA may modify this Plan up to,  but
not  after,  the termination of the Meeting to add as  Qualifying
Holdcos  any  corporations  that, in the  sole  judgment  of  the
Corporation,  meet  the  requirements of  Section  2.1.2  of  the
Combination  Agreement,  such modification  to  be  evidenced  by
adding  the  name of each such Qualifying Holdco  to  Appendix  B
hereto.

      (c)  Any amendment, modification or supplement to this Plan
of  Arrangement  that  is  approved by the  Court  following  the
Meeting shall be effective only if (i) it is consented to by each
of  the Corporation, MDA and Orbital and (ii) it is consented  to
by  the holders of the MDA Common Shares, the holders of the  MDA
1988  Options  and  the holders of the shares of  any  Qualifying
Holdcos, in each case to the extent so required by the Court.





               APPENDIX A TO PLAN OF ARRANGEMENT


        PROVISIONS ATTACHING TO THE EXCHANGEABLE SHARES

            The  Exchangeable  Shares  in  the  capital  of   the
Corporation   shall   have  the  following  rights,   privileges,
restrictions and conditions.


                           ARTICLE 1

                         INTERPRETATION

1.1       For the purposes of these share provisions:

          (a)   "Affiliate" of any person means any other  person
          directly or indirectly controlling, controlled  by,  or
          under  common  control  with,  that  person.   For  the
          purposes of this definition, "control" (including, with
          correlative    meanings,   the   terms   "controlling",
          "controlled  by" and "under common control  with"),  as
          applied  to any person, means the possession by another
          person, directly or indirectly, of the power to  direct
          or  cause  the direction of the management and policies
          of  that  first mentioned person, whether  through  the
          ownership   of  voting  securities,  by   contract   or
          otherwise.

          (b)   "Automatic Redemption Date" means November      ,
          2000, unless such date shall be accelerated at any time
          to  a  specified earlier date by the Board of Directors
          upon  at  least  75 days prior written  notice  to  the
          registered  holders of Exchangeable  Shares,  in  which
          case  the  Automatic  Redemption  Date  shall  be  such
          earlier  date;  provided, however, that  the  Board  of
          Directors  may  so accelerate the Automatic  Redemption
          Date  only at such time as there are outstanding  fewer
          than  400,000 Exchangeable Shares held by holders other
          than Orbital and its Affiliates.

          (c)   "Board of Directors" means the board of directors
          of the Corporation.

          (d)   "Business  Day"  means  any  day  other  than   a
          Saturday, a Sunday or a day when banks are not open for
          business in one or both of the Commonwealth of Virginia
          and Vancouver, British Columbia.

          (e)   "Canadian Dollar Equivalent" means in respect  of
          an amount expressed in a foreign currency (the "Foreign
          Currency  Amount") at any date the product obtained  by
          multiplying (a) the Foreign Currency Amount by (b)  the
          noon  spot exchange rate on such date for such  foreign
          currency  expressed in Canadian dollars as reported  by
          the  Bank of Canada or, in the event such spot exchange
          rate  is not available, such exchange rate on such date
          for such foreign currency expressed in Canadian dollars
          as  may  be  deemed  by the Board of  Directors  to  be
          appropriate for such purpose.

          (f)   "Capital Reorganization" has the meaning ascribed
          thereto in section 9.2 of these share provisions.

          (g)  "CBCA" means the Canada Business Corporations Act,
          as amended from time to time.

          (h)   "Corporation" means MacDonald Dettwiler  Holdings
          Inc.  (formerly  known  as  3173623  Canada  Inc.),   a
          corporation incorporated under the CBCA.

          (i)   "Current  Market Price" means, in respect  of  an
          Orbital  Common Share on any date, the Canadian  Dollar
          Equivalent of the closing sale price of Orbital  Common
          Shares  on such day (or, if no trades of Orbital Common
          Shares  occurred on such day, on the last  trading  day
          prior  thereto on which such trades occurred)  reported
          on  NASDAQ,  or, if the Orbital Common Shares  are  not
          then quoted on NASDAQ, on such other stock exchange  or
          automated quotation system on which the Orbital  Common
          Shares are listed or quoted, as the case may be, as may
          be selected by the Board of Directors for such purpose;
          provided, however, that if in the opinion of the  Board
          of   Directors  the  public  distribution  or   trading
          activity  of  Orbital Common Shares during such  period
          does  not create a market that reflects the fair market
          value  of  an  Orbital Common Share, then  the  Current
          Market  Price  of  an  Orbital Common  Share  shall  be
          determined  by  the Board of Directors based  upon  the
          advice of such qualified independent financial advisors
          as  the  Board of Directors may deem to be appropriate,
          and  provided further that any such selection,  opinion
          or  determination  by the Board of Directors  shall  be
          conclusive and binding.

          (j)   "Current Orbital Common Share Equivalent"  means,
          on  any  date, the equivalent as at such  date  of  one
          Orbital   Common  Share  as  at  the  Effective   Date,
          expressed   to  four  decimal  places,  determined   by
          applying   on   a   cumulative  basis   the   following
          adjustments, to the extent applicable by reason of  any
          transactions  occurring in respect  of  Orbital  Common
          Shares  between the Effective Date and such  date,  the
          Current  Orbital  Common Share  Equivalent  as  at  the
          Effective Date being 1.0000:

                           (i)         if   Orbital   shall   (A)
               subdivide, redivide or change its then outstanding
               Orbital  Common  Shares into a greater  number  of
               Orbital  Common Shares, unless the Corporation  is
               permitted under applicable law without a  vote  of
               its shareholders to make, and shall simultaneously
               make,  the  same  or  an  economically  equivalent
               change   to   the   rights  of  the   holders   of
               Exchangeable   Shares,   (B)   reduce,    combine,
               consolidate or change its then outstanding Orbital
               Common  Shares  into a lesser  number  of  Orbital
               Common Shares, unless the Corporation is permitted
               under  applicable  law  without  a  vote  of   its
               shareholders  to  make, and  shall  simultaneously
               make,  the  same  or  an  economically  equivalent
               change   to   the   rights  of  the   holders   of
               Exchangeable  Shares, or (C) issue Orbital  Common
               Shares  (or securities exchangeable or convertible
               into Orbital Common Shares) to the holders of  all
               or  substantially  all  of  its  then  outstanding
               Orbital Common Shares by way of stock dividend  or
               other  distribution  (other  than  to  holders  of
               Orbital  Common Shares who exercise an  option  to
               receive stock dividends in lieu of receiving  cash
               dividends),  unless the Corporation  is  permitted
               under  applicable  law  without  a  vote  of   its
               shareholders  to  issue or distribute,  and  shall
               simultaneously  issue  and distribute,  equivalent
               numbers   of  Orbital  Common  Shares   or   other
               securities  (adjusted if necessary  in  accordance
               with the Current Orbital Common Share Equivalent),
               or  the  economic equivalent on a per share basis,
               to  the holders of the Exchangeable Shares (any of
               such events being herein called an "Orbital Common
               Share Reorganization"), the Current Orbital Common
               Share   Equivalent  shall  be  adjusted  effective
               immediately  after the record date  at  which  the
               holders  of  Orbital Common Shares are  determined
               for  the  purpose  of  the  Orbital  Common  Share
               Reorganization by multiplying the Current  Orbital
               Common  Share Equivalent in effect on such  record
               date by the quotient obtained when:

                                          (I)    the  number   of
                    Orbital  Common Shares outstanding after  the
                    completion  of  such  Orbital  Common   Share
                    Reorganization (but before giving  effect  to
                    the issue of any Orbital Common Shares issued
                    after such record date otherwise than as part
                    of  such Orbital Common Share Reorganization)
                    including,   in  the  case  where  securities
                    exchangeable  or  convertible  into   Orbital
                    Common Shares are distributed, the number  of
                    Orbital  Common Shares that would  have  been
                    outstanding   had   such   securities    been
                    exchanged  for  or  converted  into   Orbital
                    Common Shares on such record date,

             is divided by

                                          (II)   the  number   of
                    Orbital  Common  Shares outstanding  on  such
                    record  date  before  giving  effect  to  the
                    Orbital Common Share Reorganization;

                          (ii)       if at any time Orbital shall
               fix  a  record  date for the issuance  of  rights,
               options  or  warrants to the  holders  of  all  or
               substantially  all  of the Orbital  Common  Shares
               entitling  them  to subscribe for or  to  purchase
               Orbital  Common Shares (or securities  of  Orbital
               convertible into Orbital Common Shares) at a price
               per  Orbital Common Share (or having a  conversion
               price  per Orbital Common Share) of less than  the
               Pre-Dilution  Market Price on  such  record  date,
               unless   the   Corporation  is   permitted   under
               applicable  law without a vote of its shareholders
               to   issue,   and   shall  simultaneously   issue,
               equivalent  numbers  of such  rights,  options  or
               warrants, adjusted if necessary in accordance with
               the  Current  Orbital Common Share  Equivalent  at
               such  record  date,  or  the  economic  equivalent
               thereof  on  a per share basis, to the holders  of
               Exchangeable  Shares (any such event being  herein
               referred  to  as  a "Rights Offering"),  then  the
               Current  Orbital Common Share Equivalent  then  in
               effect  shall be adjusted immediately  after  such
               record  date  by  multiplying the Current  Orbital
               Common  Share Equivalent in effect on such  record
               date by the quotient obtained when:

                                          (A)   the  sum  of  the
                    number  of  Orbital Common Shares outstanding
                    on   such  record  date  and  the  number  of
                    additional Orbital Common Shares offered  for
                    subscription  or  purchase under  the  Rights
                    Offering  (or  the number of  Orbital  Common
                    Shares  into which the securities so  offered
                    are convertible)

          is divided by

                                          (B)   the  sum  of  the
                    number  of  Orbital Common Shares outstanding
                    on such record date and the number determined
                    by  dividing the aggregate price of the total
                    number  of  additional Orbital Common  Shares
                    offered  for  subscription or purchase  under
                    the   Rights   Offering  (or  the   aggregate
                    conversion    price   of   the    convertible
                    securities  so  offered) by the  Pre-Dilution
                    Market Price on such record date.

                                   Any Orbital Common Share owned
               by  or  held for the account of Orbital  shall  be
               deemed  not  to be outstanding for the purpose  of
               any such computation.  If such rights, options  or
               warrants are not so issued or if, at the  date  of
               expiry  of the rights, options or warrants subject
               to  the Rights Offering, less than all the rights,
               options or warrants have been exercised, then  the
               Current  Orbital Common Share Equivalent shall  be
               readjusted effective immediately after the date of
               expiry   to  the  Current  Orbital  Common   Share
               Equivalent which would have been in effect if such
               record  date had not been fixed or to the  Current
               Orbital  Common Share Equivalent which would  then
               be  in  effect on the date of expiry if  the  only
               rights, options or warrants issued had been  those
               that were exercised, as the case may be;

                          (iii)     if Orbital shall fix a record
               date for the making of a distribution (including a
               distribution  by  way of stock  dividend)  to  the
               holders   of   all   or  substantially   all   its
               outstanding Orbital Common Shares of

                                        (A)  shares of Orbital of
                    any  class  other than Orbital Common  Shares
                    (or  shares  convertible into Orbital  Common
                    Shares referred to in (i) (C) above),

                                         (B)  rights, options  or
                    warrants (excluding a Rights Offering),

                                         (C)   evidences  of  its
                    indebtedness      (excluding     indebtedness
                    convertible   into  Orbital   Common   Shares
                    referred to in (i) (C) above) or

                                         (D)   any  other  assets
                    (other than any of the distributions referred
                    to  in (A), (B) or (C), dividends paid in the
                    ordinary  course or an Orbital  Common  Share
                    Reorganization)

                                     unless  the  Corporation  is
               permitted under applicable law without a  vote  of
               its   shareholders   to  distribute,   and   shall
               simultaneously  distribute,  the  same  number  of
               shares, rights, options or warrants, evidences  of
               indebtedness or other assets, as the case may  be,
               adjusted  if  necessary  in  accordance  with  the
               Current Orbital Common Share Equivalent as at such
               record date, or the economic equivalent thereof on
               a  per share basis, to the holders of Exchangeable
               Shares (any such event being herein referred to as
               a "Special Distribution") then, in each such case,
               the  Current Orbital Common Share Equivalent shall
               be adjusted effective immediately after the record
               date at which the holders of Orbital Common Shares
               are  determined  for the purposes of  the  Special
               Distribution  by  multiplying the Current  Orbital
               Common  Share Equivalent in effect on such  record
               date by the quotient obtained when:

                                        (I)  the product obtained
                    when  the  number  of Orbital  Common  Shares
                    outstanding on the record date is  multiplied
                    by  the  Pre-Dilution Market  Price  on  such
                    date,

             is divided by

                                          (II)   the   difference
                    obtained   when  the  amount  by  which   the
                    aggregate fair market value (as determined by
                    the  Board  of Directors, which determination
                    shall  be conclusive) of the shares,  rights,
                    options,  warrants, evidences of indebtedness
                    or assets, as the case may be, distributed in
                    the  Special  Distribution exceeds  the  fair
                    market  value (as determined by the Board  of
                    Directors,  which  determination   shall   be
                    conclusive)  of  the consideration,  if  any,
                    received  therefor by Orbital, is  subtracted
                    from the product obtained when the number  of
                    Orbital  Common  Shares  outstanding  on  the
                    record date is multiplied by the Pre-Dilution
                    Market Price on such date,

                provided that no such adjustment shall be made if
          the  result of such adjustment would be to decrease the
          Current  Orbital  Common  Share  Equivalent  in  effect
          immediately  before  such  record  date.   Any  Orbital
          Common  Share  owned  by or held  for  the  account  of
          Orbital  shall be deemed not to be outstanding for  the
          purpose of any such computation.  Such adjustment shall
          be  made  successively whenever such a record  date  is
          fixed.  To the extent that such distribution is not  so
          made, the Current Orbital Common Share Equivalent shall
          be  readjusted  effective immediately  to  the  Current
          Orbital Common Share Equivalent which would then be  in
          effect  based  upon such shares or rights,  options  or
          warrants   or  evidences  of  indebtedness  or   assets
          actually distributed.

          (k)   "Effective Date" has the meaning ascribed thereto
          in the Plan of Arrangement.

          (l)    "Exchangeable  Shares"  mean  the   Exchangeable
          Non-Voting Shares of the Corporation having the rights,
          privileges,  restrictions  and  conditions  set   forth
          herein.

          (m)   "Lien"  has the meaning ascribed thereto  in  the
          Plan of Arrangement.

          (n)   "Liquidation  Amount" has  the  meaning  ascribed
          thereto in section 4.1 of these share provisions.

          (o)   "Liquidation Call Right" has the meaning ascribed
          thereto in section 5.2 of the Plan of Arrangement.

          (p)  "NASDAQ" means the NASDAQ National Market System;

          (q)    "Liquidation  Date"  has  the  meaning  ascribed
          thereto in section 4.1 of these share provisions.

          (r)   "Orbital"  means Orbital Sciences Corporation,  a
          corporation  organized and existing under the  laws  of
          the State of Delaware, and any successor corporation.

          (s)   "Orbital  Call Notice" has the  meaning  ascribed
          thereto   in   subsection  5.1(b)  of   the   Plan   of
          Arrangement.

          (t)   "Orbital  Common  Share Reorganization"  has  the
          meaning ascribed thereto in subsection 1.1(j) of  these
          share provisions.

          (u)   "Orbital Common Shares" mean the shares of common
          stock  of  Orbital, with a par value  of  U.S.$.01  per
          share  and  having one vote per share,  and  any  other
          securities into which such shares may be changed.

          (v)  "Orbital Dividend Declaration Date" means the date
          on which the Board of Directors of Orbital declares any
          dividend on the Orbital Common Shares.

          (w)   "Orbital  Special Share" means the one  share  of
          Special  Voting Preferred Stock of Orbital with  a  par
          value  of U.S.$.01 and having voting rights at meetings
          of holders of Orbital Common Shares equal to the number
          of  Exchangeable Shares outstanding from time  to  time
          (other than Exchangeable Shares held by Orbital and its
          Affiliates) to be issued to, and voted by, the  Trustee
          pursuant to the Voting Trust and Exchange Agreement.

          (x)    "Plan   of  Arrangement"  means  the   plan   of
          arrangement   relating  to  the  arrangement   of   the
          Corporation  under section 192 of the  CBCA,  to  which
          plan these share provisions are attached.

          (y)   "Pre-Dilution Market Price" means, in respect  of
          an  Orbital  Common  Share on any  date,  the  Canadian
          Dollar  Equivalent of the average of the  closing  sale
          prices  as reported on NASDAQ of such shares  during  a
          period  of  20 consecutive trading days ending  on  the
          fourth  trading  day prior to such  date,  or,  if  the
          Orbital Common Shares are not then quoted on NASDAQ, on
          such other stock exchange or automated quotation system
          on which the Orbital Common Shares are listed or quoted
          as  may be selected by the Board of Directors for  such
          purpose;  provided, however, that if in the opinion  of
          the  Board  of  Directors  the public  distribution  or
          trading  activity of Orbital Common Shares during  such
          period does not create a market that reflects the  fair
          market value of an Orbital Common Share, then the  Pre-
          Dilution Market Price of an Orbital Common Share  shall
          be  determined by the Board of Directors based upon the
          advice of such qualified independent financial advisors
          as  the  Board of Directors may deem to be appropriate,
          and  provided further that any such selection,  opinion
          or  determination  by the Board of Directors  shall  be
          conclusive and binding;

          (z)   "Redemption Call Right" has the meaning  ascribed
          thereto in section 5.3 of the Plan of Arrangement.

          (aa)   "Redemption  Price"  has  the  meaning  ascribed
          thereto in section 6.1 of these share provisions.

          (bb)   "Retracted  Shares"  has  the  meaning  ascribed
          thereto in section 5.1 of these share provisions.

          (cc)  "Retraction Call Right" has the meaning  ascribed
          thereto in section 5.1 of the Plan of Arrangement.

          (dd) "Retraction Date" has the meaning ascribed thereto
          in section 5.2 of these share provisions.

          (ee)   "Retraction  Price"  has  the  meaning  ascribed
          thereto in section 5.1 of these share provisions.

          (ff)  "Retraction  Request" has  the  meaning  ascribed
          thereto in section 5.1 of these share provisions.

          (gg) "Rights Offering" has the meaning ascribed thereto
          in subsection 1.1(j) of these share provisions.

          (hh)  "Special  Distribution" has the meaning  ascribed
          thereto in subsection 1.1(j) of these share provisions.

          (ii)  "Support  Agreement" means the Support  Agreement
          between  Orbital and the Corporation, made  as  of  the
          Effective Date.

          (jj)  "Transfer Agent" means Montreal Trust Company  of
          Canada or such other person as may from time to time be
          the  registrar and transfer agent for the  Exchangeable
          Shares.

          (kk)  "Trustee"  means  State  Street  Bank  and  Trust
          Company, and any successor trustee appointed under  the
          Voting and Exchange Trust Agreement.

          (ll)  "Voting and Exchange Trust Agreement"  means  the
          Voting   and  Exchange  Trust  Agreement  between   the
          Corporation, Orbital and the Trustee, made  as  of  the
          Effective Date.

1.2       All amounts required to be paid, deposited or delivered
hereunder  shall be paid, deposited or delivered after  deduction
of  any  amount  required by applicable law  to  be  deducted  or
withheld on account of tax and the deduction of such amounts  and
remittance to the applicable tax authorities shall, to the extent
thereof,  satisfy  such requirement to pay,  deposit  or  deliver
hereunder.


                           ARTICLE 2

                 RANKING OF EXCHANGEABLE SHARES

2.1        The  Exchangeable  Shares shall  rank  senior  to  the
Class  B  Preferred Shares and the Common Shares  and  any  other
shares ranking junior to the Exchangeable Shares, with respect to
the  payment of dividends and the distribution of assets  in  the
event  of  the  liquidation, dissolution  or  winding-up  of  the
Corporation,  whether  voluntary or  involuntary,  or  any  other
distribution  of  the  assets  of  the  Corporation   among   its
shareholders for the purpose of winding up its affairs.


                           ARTICLE 3

                           DIVIDENDS

3.1       A holder of an Exchangeable Share shall be entitled  to
receive  and the Board of Directors shall, subject to  applicable
law,  declare a dividend on each Exchangeable Share  (a)  in  the
case of a cash dividend declared on the Orbital Common Shares, in
an  amount  in  cash  for each Exchangeable Share  equal  to  the
Canadian  Dollar  Equivalent on the Orbital Dividend  Declaration
Date  of  the  cash dividend declared on such number  of  Orbital
Common  Shares  as is equal to the Current Orbital  Common  Share
Equivalent on the Orbital Dividend Declaration Date or (b) in the
case of a stock dividend declared on the Orbital Common Shares to
be  paid  in  Orbital  Common Shares, in  such  whole  number  of
Exchangeable  Shares  for the Exchangeable Shares  held  by  each
holder as is equal to the number of Orbital Common Shares  to  be
paid as a dividend per Orbital Common Shares (if such calculation
results in a fraction of an Exchangeable Share, the holder  shall
receive in lieu of such fraction an amount in cash equal  to  the
product  obtained by multiplying the amount that would be payable
in  respect of an equal fraction of an Orbital Common Share as at
the  Orbital Dividend Declaration Date, calculated in  accordance
with  section 9.4, by the Current Orbital Common Share Equivalent
as at such date) or (c) in the case of a dividend declared on the
Orbital  Common Shares to be paid in property other than cash  or
Orbital   Common  Shares  (including  without  limitation   other
securities  of Orbital), in such type and amount of property  for
each  Exchangeable  Share  as  is the  same  as  or  economically
equivalent (as determined by the Board of Directors in accordance
with  section 9.1) to the type and amount of property to be  paid
as a dividend on such number of Orbital Common Shares as is equal
to  the  Current Orbital Common Share Equivalent on  the  Orbital
Dividend Declaration Date.  Such dividends shall be paid  out  of
money,  assets or property of the Corporation properly applicable
to  the  payment of dividends, or out of authorized but  unissued
Exchangeable Shares.

3.2       Cheques of the Corporation payable at par at any branch
of  the bankers of the Corporation shall be issued in respect  of
any cash dividends contemplated by subsection 3.1(a) hereof or in
respect  of  any  cash  amount payable in lieu  of  a  fractional
Exchangeable  Share  in  connection  with  any  stock   dividends
contemplated by subsection 3.1(b) hereof and the sending of  such
a  cheque  to each holder of an Exchangeable Share shall  satisfy
the  cash dividend represented thereby unless the cheque  is  not
paid on presentation.  Certificates registered in the name of the
registered  holder  of Exchangeable Shares  shall  be  issued  or
transferred  in  respect of any stock dividends  contemplated  by
subsection 3.1(b) hereof and the sending of such a certificate to
each  holder  of  an Exchangeable Share shall satisfy  the  stock
dividend  represented thereby.  Such other  type  and  amount  of
property   in   respect   of   any  dividends   contemplated   by
subsection   3.1(c)  hereof  shall  be  issued,  distributed   or
transferred  by  the  Corporation in  such  manner  as  it  shall
determine  and the issuance, distribution or transfer thereof  by
the  Corporation  to each holder of an Exchangeable  Share  shall
satisfy  the  dividend  represented thereby.   No  holder  of  an
Exchangeable  Share  shall be entitled to recover  by  action  or
other legal process against the Corporation any dividend that  is
represented by a cheque that has not been duly presented  to  the
Corporation's  bankers  for  payment or  that  otherwise  remains
unclaimed  for a period of six years from the date on which  such
dividend was payable.

3.3       The record date for the determination of the holders of
Exchangeable  Shares  entitled to receive  payment  of,  and  the
payment  date  for,  any dividend declared  on  the  Exchangeable
Shares  under section 3.1 hereof shall be the same dates  as  the
record date and payment date, respectively, for the corresponding
dividend declared on the Orbital Common Shares.

3.4        If  on any payment date for any dividends declared  on
the  Exchangeable Shares under section 3.1 hereof  the  dividends
are  not  paid  in  full on all of the Exchangeable  Shares  then
outstanding, any such dividends that remain unpaid shall be  paid
on  a  subsequent  date  or  dates determined  by  the  Board  of
Directors on which the Corporation shall have sufficient  moneys,
assets  or  property properly applicable to the payment  of  such
dividends.

3.5         So  long  as  any  of  the  Exchangeable  Shares  are
outstanding,  the Corporation shall not at any time without,  but
may  at  any  time  with,  the approval of  the  holders  of  the
Exchangeable  Shares given as specified in section 8.2  of  these
share provisions:

          (a)   pay any dividends on the Class B Preferred Shares
          or  the  Common  Shares, or any  other  shares  ranking
          junior  to  the Exchangeable Shares, other  than  stock
          dividends  payable in Common Shares or any  such  other
          shares  ranking junior to the Exchangeable  Shares,  as
          the case may be;

          (b)    redeem   or   purchase  or  make   any   capital
          distribution in respect of Class B Preferred Shares  or
          Common Shares or any other shares ranking junior to the
          Exchangeable Shares;

          (c)   redeem  or  purchase  any  other  shares  of  the
          Corporation   ranking  equally  with  the  Exchangeable
          Shares with respect to the payment of dividends  or  on
          any liquidation distribution;

          (d)   issue any Exchangeable Shares other than  (i)  by
          way   of  stock  dividends  to  the  holders  of   such
          Exchangeable Shares, (ii) otherwise pro rata to holders
          of  Exchangeable Shares, (iii) as contemplated  by  the
          Support Agreement or (iv) pursuant to any agreements or
          rights in existence at the Effective Date; or

          (e)   issue any other shares of the Corporation ranking
          equally with or senior to the Exchangeable Shares;

provided that the restrictions in subsections 3.5(a), 3.5(b)  and
3.5(c)  shall  not  apply  if all dividends  on  the  outstanding
Exchangeable Shares corresponding to dividends declared  to  date
on  the  Orbital  Common Shares shall have been declared  on  the
Exchangeable Shares and paid in full.


                           ARTICLE 4

                  DISTRIBUTION ON LIQUIDATION

4.1        In  the  event  of  the  liquidation,  dissolution  or
winding-up  of the Corporation or any other distribution  of  the
assets  of the Corporation among its shareholders for the purpose
of  winding up its affairs, a holder of Exchangeable Shares shall
be  entitled,  subject to applicable law,  to  receive  from  the
assets  of the Corporation in respect of each Exchangeable  Share
held  by  such  holder  on the effective date  (the  "Liquidation
Date") of such liquidation, dissolution or winding-up, before any
distribution  of any part of the assets of the Corporation  among
the holders of the Class B Preferred Shares, the Common Shares or
any  other  shares ranking junior to the Exchangeable Shares,  an
amount per share equal to (a) the Current Market Price multiplied
by  the  Current Orbital Common Share Equivalent,  in  each  case
determined  on the Liquidation Date, which shall be satisfied  in
full  in  respect of all of the Exchangeable Shares held by  such
holder  by the Corporation causing to be delivered to such holder
such  whole  number of Orbital Common Shares as is equal  to  the
product  obtained by multiplying the number of such  Exchangeable
Shares  by  the Current Orbital Common Share Equivalent (together
with  an  amount in lieu of any fractional Orbital  Common  Share
resulting  from  such  calculation  payable  in  accordance  with
section  9.4), plus (b) the aggregate of all declared and  unpaid
dividends  on each such Exchangeable Share up to the  Liquidation
Date (collectively the "Liquidation Amount").

4.2        On or promptly after the Liquidation Date, and subject
to  the  exercise by Orbital of the Liquidation Call  Right,  the
Corporation  shall cause to be delivered to the  holders  of  the
Exchangeable  Shares  the  Liquidation  Amount  for   each   such
Exchangeable  Share  upon  presentation  and  surrender  of   the
certificates representing such Exchangeable Shares, together with
such other documents and instruments as may be required to effect
a  transfer of Exchangeable Shares under the CBCA and the by-laws
of  the Corporation and such additional documents and instruments
as  the  Transfer Agent may reasonably require, at the registered
office of the Corporation or at any office of the Transfer  Agent
as  may  be specified by the Corporation by notice to the holders
of  the  Exchangeable Shares.  Payment of the  total  Liquidation
Amount for such Exchangeable Shares shall be made by delivery  to
each  holder,  at  the  address of the  holder  recorded  in  the
securities  register  of  the Corporation  for  the  Exchangeable
Shares  or by holding for pick-up by the holder at the registered
office of the Corporation or at any office of the Transfer  Agent
as  may  be specified by the Corporation by notice to the holders
of   Exchangeable  Shares,  on  behalf  of  the  Corporation   of
certificates  representing  the  Orbital  Common  Shares  to   be
delivered  in payment thereof (which shares shall be duly  issued
as  fully paid and non-assessable and shall be free and clear  of
any  Liens) and a cheque of the Corporation payable at par at any
branch  of  the  bankers of the Corporation  in  respect  of  any
fractional  Orbital  Common Share and  all  declared  and  unpaid
dividends comprising part of the total Liquidation Amount (or, if
any of such dividends were payable in property, such property  or
property that is the same as or economically equivalent  to  such
property).  On and after the Liquidation Date, the holders of the
Exchangeable   Shares  shall  cease  to  be   holders   of   such
Exchangeable Shares and shall not be entitled to exercise any  of
the rights of holders in respect thereof, other than the right to
receive  the  total  Liquidation  Amount  in  respect  of   their
Exchangeable  Shares,  unless payment of  the  total  Liquidation
Amount  for  such  Exchangeable Shares shall  not  be  made  upon
presentation  and surrender of share certificates  in  accordance
with  the foregoing provisions, in which case the rights  of  the
holders  shall  remain  unaffected until  the  total  Liquidation
Amount  has  been paid in the manner hereinbefore provided.   The
Corporation  shall have the right at any time  on  or  after  the
Liquidation  Date to deposit or cause to be deposited  the  total
Liquidation   Amount  in  respect  of  the  Exchangeable   Shares
represented by certificates that have not at the Liquidation Date
been  surrendered  by the holders thereof in a custodial  account
with  any  chartered bank or trust company in Canada.  Upon  such
deposit  being  made, the rights of the holders  of  Exchangeable
Shares after such deposit shall be limited to receiving the total
Liquidation  Amount  (without  interest)  for  such  Exchangeable
Shares  so deposited, against presentation and surrender  of  the
said  certificates held by them, respectively, in accordance with
the  foregoing provisions.  Upon such payment or deposit  of  the
total  Liquidation Amount, the holders of the Exchangeable Shares
shall thereafter be considered and deemed for all purposes to  be
the holders of the Orbital Common Shares delivered to them.

4.3       After the Corporation has satisfied its obligations  to
pay the holders of the Exchangeable Shares the Liquidation Amount
per  Exchangeable Share pursuant to section 4.1  of  these  share
provisions,  such holders shall not be entitled to share  in  any
further distribution of the assets of the Corporation.


                           ARTICLE 5

          RETRACTION OF EXCHANGEABLE SHARES BY HOLDER

5.1        A  holder of Exchangeable Shares shall be entitled  at
any  time,  subject to the exercise by Orbital of the  Retraction
Call  Right and otherwise upon compliance with the provisions  of
this  Article 5, to require the Corporation to redeem any or  all
of  the Exchangeable Shares registered in the name of such holder
(the  "Retracted Shares") for an amount for each Retracted  Share
equal  to (a) the Current Market Price multiplied by the  Current
Orbital Common Share Equivalent, in each case determined  on  the
Retraction  Date, which shall be satisfied in full in respect  of
the  Retracted Shares by the Corporation causing to be  delivered
to  such holder such whole number of Orbital Common Shares as  is
equal  to  the  product  obtained by multiplying  the  number  of
Retracted  Shares by the Current Orbital Common Share  Equivalent
(together with an amount in lieu of any fractional Orbital Common
Share resulting from such calculation payable in accordance  with
section  9.4),  plus (b) the aggregate of all dividends  declared
and  unpaid  on  each Retracted Share up to the  Retraction  Date
(collectively the "Retraction Price", provided that if the record
date for any such declared and unpaid dividend occurs on or after
the  Retraction Date the Retraction Price shall not include  such
declared  and unpaid dividends).  To effect such redemption,  the
holder  shall present and surrender at any office of the Transfer
Agent listed on Schedule A hereto the certificate or certificates
representing the Exchangeable Shares which the holder desires  to
have  the  Corporation redeem, together with such other documents
and  instruments  as  may be required to  effect  a  transfer  of
Exchangeable  Shares  under  the CBCA  and  the  by-laws  of  the
Corporation and such additional documents and instruments as  the
Transfer Agent may reasonably require, and together with  a  duly
executed  statement (the "Retraction Request")  in  the  form  of
Schedule  A hereto or in such other form as may be acceptable  to
the Transfer Agent:

          (a)   specifying that the holder desires  to  have  the
          Retracted  Shares  represented by such  certificate  or
          certificates redeemed by the Corporation; and

          (b)  acknowledging the Retraction Call Right of Orbital
          to  purchase  all but not less than all  the  Retracted
          Shares directly from the holder and that the Retraction
          Request  shall be deemed to be an irrevocable offer  by
          the  holder to sell the Retracted Shares to Orbital  in
          accordance with the Retraction Call Right.

5.2        Subject  to the exercise by Orbital of the  Retraction
Call  Right,  upon receipt by the Transfer Agent  in  the  manner
specified  in section 5.1 hereof of a certificate or certificates
representing the number of Exchangeable Shares which  the  holder
desires to have the Corporation redeem, together with such  other
documents  and  instruments  as  may  be  required  pursuant   to
section  5.1  and  a  Retraction Request, the  Corporation  shall
redeem the Retracted Shares effective at the close of business on
the  sixth Business Day after the Retraction Request is  received
(the  "Retraction Date") and shall cause to be delivered to  such
holder  the  total Retraction Price with respect to such  shares.
If  only  a  part of the Exchangeable Shares represented  by  any
certificate are redeemed (or purchased by Orbital pursuant to the
Retraction Call Right), a new certificate for the balance of such
Exchangeable Shares shall be issued to the holder at the  expense
of the Corporation.

5.3        Upon  receipt by the Transfer Agent  of  a  Retraction
Request,  the  Transfer  Agent  shall  forthwith  notify  Orbital
thereof.  In order to exercise the Retraction Call Right, Orbital
must  deliver an Orbital Call Notice to the Transfer Agent  prior
to  the expiry of the third Business Day after the receipt by the
Transfer Agent of the Retraction Request.  If Orbital does not so
notify  the  Transfer Agent, the Transfer Agent will  notify  the
holder  as  soon  as possible thereafter that  Orbital  will  not
exercise  the  Retraction Call Right.  If  Orbital  delivers  the
Orbital  Call  Notice before the end of such three  Business  Day
period, the Retraction Request shall thereupon be considered only
to  be  an  offer by the holder to sell the Retracted  Shares  to
Orbital  in accordance with the Retraction Call Right.   In  such
event, the Corporation shall not redeem the Retracted Shares  and
Orbital  shall  purchase from such holder and such  holder  shall
sell  to  Orbital  on  the Retraction Date the  Retracted  Shares
pursuant to the Retraction Call Right.

5.4        If  a  Retraction Request is received by the  Transfer
Agent  pursuant to section 5.1 and Orbital has not exercised  the
Retraction  Call Right, the Corporation shall cause the  Transfer
Agent  to deliver to the holder of the Retracted Shares,  at  the
address of the holder recorded in the securities register of  the
Corporation  for  the  Exchangeable  Shares  or  at  the  address
specified  in the holder's Retraction Request or by  holding  for
pick-up  by  the  holder at the office of the Transfer  Agent  to
which   the   Retraction  Request  was  delivered,   certificates
representing  the  Orbital Common Shares to be delivered  to  the
holder in payment of the total Retraction Price for the Retracted
Shares  (or the portion thereof payable in Orbital Common Shares,
as  the case may be) (which shares shall be duly issued as  fully
paid and non-assessable and shall be free and clear of any Liens)
registered in the name of the holder or in such other name as the
holder may request and a cheque of the Corporation payable at par
at any branch of the bankers of the Corporation in payment of the
remaining portion, if any, of the total Retraction Price (or,  if
any part of the Retraction Price consists of dividends payable in
property,  such  property or property that  is  the  same  as  or
economically equivalent to such property), and such  delivery  of
such certificates and cheque (and property, if any) on behalf  of
the  Corporation  by the Transfer Agent shall  be  deemed  to  be
payment of and shall satisfy and discharge all liability for  the
total   Retraction  Price,  to  the  extent  that  the  same   is
represented by such share certificates and cheque (and  property,
if any), unless such cheque is not paid on due presentation.

5.5        On  and  after the close of business on the Retraction
Date,  the  holder of the Retracted Shares shall cease  to  be  a
holder  of  such  Retracted Shares and shall not be  entitled  to
exercise any of the rights of a holder in respect thereof,  other
than  the  right to receive his proportionate part of  the  total
Retraction  Price,  unless  upon presentation  and  surrender  of
certificates in accordance with the foregoing provisions, payment
of  the  total Retraction Price shall not be made, in which  case
the rights of such holder shall remain unaffected until the total
Retraction  Price  has  been  paid  in  the  manner  hereinbefore
provided.   On and after the close of business on the  Retraction
Date,  provided  that presentation and surrender of  certificates
and  payment  of  the total Retraction Price  has  been  made  in
accordance  with  the foregoing provisions,  the  holder  of  the
Retracted  Shares so redeemed by the Corporation shall thereafter
be  considered and deemed for all purposes to be a holder of  the
Orbital Common Shares delivered to it.

5.6       Notwithstanding any other provision of this Article  5,
the Corporation shall not be obligated to redeem Retracted Shares
specified by a holder in a Retraction Request to the extent  that
such redemption of Retracted Shares would be contrary to solvency
requirements  or  other  provisions of applicable  law.   If  the
Corporation believes that on any Retraction Date it would not  be
permitted  by  any  of  such provisions to redeem  the  Retracted
Shares  tendered for redemption on such date, and  provided  that
Orbital  shall not have exercised the Retraction Call Right  with
respect  to  the  Retracted  Shares,  the  Corporation  shall  be
obligated to redeem Retracted Shares specified by a holder  in  a
Retraction Request only to the extent of the maximum number  that
may be so redeemed (rounded down to a whole number of shares)  as
would not be contrary to such provisions on a pro rata basis  and
shall  notify the holder at least two Business Days prior to  the
Retraction  Date as to the number of Retracted Shares which  will
not  be  redeemed  by the Corporation and the  Corporation  shall
issue  to  each holder of Retracted Shares a new certificate,  at
the expense of the Corporation, representing the Retracted Shares
not  redeemed by the Corporation pursuant to section 5.2  hereof.
The  holder  of  any such Retracted Shares not  redeemed  by  the
Corporation pursuant to section 5.2 of these share provisions  as
a  result  of  solvency requirements of applicable law  shall  be
deemed  by  giving the Retraction Request to require  Orbital  to
purchase such Retracted Shares from such holder pursuant  to  the
Exchange  Right  (as  defined in the Voting  and  Exchange  Trust
Agreement).


                           ARTICLE 6

               REDEMPTION OF EXCHANGEABLE SHARES

6.1        Subject  to  applicable law and if  Orbital  does  not
exercise the Redemption Call Right, the Corporation shall on  the
Automatic   Redemption  Date  redeem  the  whole  of   the   then
outstanding Exchangeable Shares for an amount per share equal  to
(a)  the  Current Market Price multiplied by the Current  Orbital
Common Share Equivalent, in each case determined on the Automatic
Redemption  Date, which shall be satisfied in full in respect  of
all   of   the  Exchangeable  Shares  held  by  each  holder   of
Exchangeable Shares by the Corporation causing to be delivered to
such  holder  such whole number of Orbital Common  Shares  as  is
equal  to the product obtained by multiplying the number of  such
Exchangeable   Shares  by  the  Current  Orbital   Common   Share
Equivalent  (together with an amount in lieu  of  any  fractional
Orbital  Common Share resulting from such calculation payable  in
accordance  with  section 9.4), plus (b)  the  aggregate  of  all
declared  and  unpaid  dividends  thereon  up  to  the  Automatic
Redemption Date (collectively the "Redemption Price").

6.2        On  or after the Automatic Redemption Date and subject
to  the  exercise  by Orbital of the Redemption Call  Right,  the
Corporation  shall cause to be delivered to the  holders  of  the
Exchangeable   Shares  the  Redemption  Price   for   each   such
Exchangeable Share upon presentation and surrender at any  office
of  the  Transfer  Agent  of the certificates  representing  such
Exchangeable  Shares,  together with  such  other  documents  and
instruments   as  may  be  required  to  effect  a  transfer   of
Exchangeable  Shares  under  the CBCA  and  the  by-laws  of  the
Corporation and such additional documents and instruments as  the
Transfer  Agent  may reasonably require.  Payment  of  the  total
Redemption  Price for such Exchangeable Shares shall be  made  by
delivery to each holder, at the address of the holder recorded in
the securities register of the Corporation or by holding for pick
up  by the holder at the registered office of the Corporation  or
at  any  office of the Transfer Agent as may be specified by  the
Corporation  in  such  notice, on behalf of  the  Corporation  of
certificates  representing  the  Orbital  Common  Shares  to   be
delivered  to the holder in payment of the Redemption  Price  (or
the portion thereof payable in Orbital Common Shares, as the case
may  be)  (which  shares shall be duly issued as fully  paid  and
non-assessable and shall be free and clear of any  Liens)  and  a
cheque  of  the Corporation payable at par at any branch  of  the
bankers  of the Corporation in respect of any fractional  Orbital
Common  Share  and  all declared and unpaid dividends  comprising
part  of the total Redemption Price (or, if any of such dividends
are  payable  in  property, such property).   On  and  after  the
Automatic Redemption Date, the holders of the Exchangeable Shares
called  for  redemption  shall  cease  to  be  holders  of   such
Exchangeable Shares and shall not be entitled to exercise any  of
the rights of holders in respect thereof, other than the right to
receive the total Redemption Price for their Exchangeable Shares,
unless   payment   of  the  total  Redemption  Price   for   such
Exchangeable  Shares  shall  not be made  upon  presentation  and
surrender  of  certificates  in  accordance  with  the  foregoing
provisions, in which case the rights of the holders shall  remain
unaffected until the total Redemption Price has been paid in  the
manner  hereinbefore provided.  The Corporation  shall  have  the
right  at any time to deposit or cause to be deposited the  total
Redemption  Price  of  the  Exchangeable  Shares  so  called  for
redemption,   or   of  such  of  the  said  Exchangeable   Shares
represented  by certificates that have not at the  date  of  such
deposit  been  surrendered by the holders thereof  in  connection
with  such  redemption, in a custodial account with any chartered
bank  or trust company in Canada named in such notice.  Upon  the
later  of  such  deposit being made and the Automatic  Redemption
Date,  the  Exchangeable Shares in respect whereof  such  deposit
shall  have  been made shall be redeemed and the  rights  of  the
holders thereof after such deposit or Automatic Redemption  Date,
as  the  case  may  be, shall be limited to receiving  the  total
Redemption  Price  for  such Exchangeable  Shares  so  deposited,
against presentation and surrender of the said certificates  held
by   them,   respectively,  in  accordance  with  the   foregoing
provisions.  Upon such payment or deposit of the total Redemption
Price, the holders of the Exchangeable Shares shall thereafter be
considered  and  deemed for all purposes to  be  holders  of  the
Orbital Common Shares delivered to them.


                           ARTICLE 7

                         VOTING RIGHTS

7.1       Except as required by applicable law and the provisions
of  sections  3.5, 8.1 and 10.2, the holders of the  Exchangeable
Shares shall not be entitled as such to receive notice of  or  to
attend any meeting of the shareholders of the Corporation  or  to
vote at any such meeting.


                           ARTICLE 8

                     AMENDMENT AND APPROVAL

8.1        The  rights, privileges, restrictions  and  conditions
attaching to the Exchangeable Shares may be added to, changed  or
removed  but  only  with  the approval  of  the  holders  of  the
Exchangeable Shares given as hereinafter specified.

8.2        Any  approval given by the holders of the Exchangeable
Shares  to  add  to,  change  or  remove  any  right,  privilege,
restriction or condition attaching to the Exchangeable Shares  or
any other matter requiring the approval or consent of the holders
of   the  Exchangeable  Shares  shall  be  deemed  to  have  been
sufficiently given if it shall have been given in accordance with
applicable  law  subject  to  a  minimum  requirement  that  such
approval  be  evidenced by resolution passed  by  not  less  than
two-thirds  of the votes cast on such resolution at a meeting  of
holders of Exchangeable Shares duly called and held at which  the
holders of at least 50% of the outstanding Exchangeable Shares at
that  time are present or represented by proxy.  If at  any  such
meeting   the   holders  of  at  least  50%  of  the  outstanding
Exchangeable  Shares at that time are not present or  represented
by  proxy within one-half hour after the time appointed for  such
meeting then the meeting shall be adjourned to such date not less
than  10  days thereafter and to such time and place  as  may  be
designated  by  the Chairman of such meeting.  At such  adjourned
meeting the holders of Exchangeable Shares present or represented
by  proxy thereat may transact the business for which the meeting
was  originally  called and a resolution passed  thereat  by  the
affirmative vote of not less than two thirds of the votes cast on
such resolution at such meeting shall constitute the approval  or
consent of the holders of the Exchangeable Shares.


                           ARTICLE 9

       ECONOMIC EQUIVALENCE; CHANGES RELATING TO ORBITAL

9.1        The Board of Directors shall determine, in good  faith
and in its sole discretion (with the assistance of such reputable
and qualified independent financial advisors and/or other experts
as  the Board of Directors may require) economic equivalence  for
the  purposes  of  any  provision herein  that  requires  such  a
determination and each such determination shall be conclusive and
binding on Orbital, where applicable.

9.2        If  at  any time there is a capital reorganization  of
Orbital  that  is  not  provided for in subsection  1.1(j)  or  a
consolidation, merger, arrangement or amalgamation (statutory  or
otherwise) of Orbital with or into another entity (any such event
being   called  a  "Capital  Reorganization"),  any   holder   of
Exchangeable  Shares  whose Exchangeable  Shares  have  not  been
exchanged  for  Orbital  Common Shares  in  accordance  with  the
provisions  hereof  prior to the record  date  for  such  Capital
Reorganization  shall be entitled to receive  and  shall  accept,
upon  any  such  exchange occurring pursuant  to  the  provisions
hereof  at  any  time  after the record  date  for  such  Capital
Reorganization,  in  lieu of the Orbital Common  Shares  that  he
would  otherwise  have been entitled to receive pursuant  to  the
provisions  hereof, the number of shares or other  securities  of
Orbital  or  of  the  body  corporate  resulting,  surviving   or
continuing  from  the Capital Reorganization, or other  property,
that  such holder would have been entitled to receive as a result
of  such  Capital Reorganization if, on the record date,  he  had
been the registered holder of the number of Orbital Common Shares
to   which  he  was  then  entitled  upon  any  exchange  of  his
Exchangeable Shares into Orbital Common Shares in accordance with
the  provisions hereof, subject to adjustment thereafter  in  the
same manner, as nearly as may be possible, as is provided for  in
subsection  1.1(j); provided that no such Capital  Reorganization
shall  be  carried into effect unless all necessary  steps  shall
have  been taken so that each holder of Exchangeable Shares shall
thereafter  be  entitled to receive, upon  any  exchange  of  his
Exchangeable  Shares  pursuant to  the  provisions  hereof,  such
number  of shares or other securities of Orbital or of  the  body
corporate  resulting, surviving or continuing  from  the  Capital
Reorganization, or other property.

9.3       In the case of any reclassification of, or other change
in,  the  outstanding Orbital Common Shares other than  a  Common
Share  Reorganization or a Capital Reorganization,  such  changes
shall be made in the rights attaching to the Exchangeable Shares,
without  any action on the part of the Corporation or the holders
of  the Exchangeable Shares to the extent permitted by applicable
law,  effective immediately following the record  date  for  such
reclassification  or  other change, to the  extent  necessary  to
ensure  that holders of Exchangeable Shares shall be entitled  to
receive,  upon the occurrence at any time after such record  date
of  any  event  whereby they would receive Orbital Common  Shares
pursuant  to  the provisions hereof, such shares,  securities  or
rights  as they would have received if their Exchangeable  Shares
had  been  exchanged for Orbital Common Shares  pursuant  to  the
provisions hereof immediately prior to such record date,  subject
to  adjustment thereafter in the same manner, as nearly as may be
possible, as is provided for in subsection 1.1(j).

9.4         No  certificates  or  scrip  representing  fractional
Orbital   Common  Shares  shall  be  delivered  to   holders   of
Exchangeable Shares pursuant to the provisions hereof.   In  lieu
of  any  such  fractional security, each  person  entitled  to  a
fractional  interest in an Orbital Common Share will  receive  an
amount  of  cash  (rounded to the nearest  whole  cent),  without
interest,  equal  to  the Canadian Dollar Equivalent  as  of  the
fourth  Business Day prior to the relevant date  of  delivery  of
certificates representing Orbital Common Shares (the  "Fractional
Share  Calculation  Date") of the product of (i)  such  fraction,
multiplied  by  (ii)  the closing sale price  of  Orbital  Common
Shares  as reported on NASDAQ on the Fractional Share Calculation
Date.


                           ARTICLE 10

       ACTIONS BY THE CORPORATION UNDER SUPPORT AGREEMENT

10.1       The Corporation will take all such actions and do  all
such  things  as shall be necessary or advisable to  perform  and
comply  with and to ensure performance and compliance by  Orbital
with  all provisions of the Support Agreement and the Voting  and
Exchange  Trust  Agreement  applicable  to  the  Corporation  and
Orbital,  respectively,  in accordance  with  the  terms  thereof
including, without limitation, taking all such actions and  doing
all such things as shall be necessary or advisable to enforce  to
the  fullest  extent  possible for  the  direct  benefit  of  the
Corporation and the holders of Exchangeable Shares all rights and
benefits in favour of the Corporation under or pursuant  to  such
agreements.

10.2       The  Corporation  shall  not  propose,  agree  to   or
otherwise  give  effect  to  any  amendment  to,  or  waiver   or
forgiveness  of  its  rights or obligations  under,  the  Support
Agreement and the Voting and Exchange Trust Agreement without the
approval  of  the  holders of the Exchangeable  Shares  given  in
accordance with section 8.2 of these share provisions other  than
such  amendments, waivers and/or forgiveness as may be  necessary
or advisable for the purposes of:

          (a)   adding  to  the covenants of the other  party  or
          parties  to  such agreement for the protection  of  the
          Corporation or the holders of Exchangeable Shares; or

          (b)    making  such  provisions  or  modifications  not
          inconsistent  with such agreements as may be  necessary
          or  desirable  with  respect to  matters  or  questions
          arising  thereunder which, in the opinion of the  Board
          of  Directors,  it may be expedient to  make,  provided
          that  the  Board of Directors shall be of the  opinion,
          after  consultation with counsel, that such  provisions
          and  modifications  will  not  be  prejudicial  to  the
          interests of the holders of the Exchangeable Shares; or

          (c)   making  such  changes in or corrections  to  such
          agreements  which,  on the advice  of  counsel  to  the
          Corporation, are required for the purpose of curing  or
          correcting  any  ambiguity or  defect  or  inconsistent
          provision  or clerical omission or mistake or  manifest
          error  contained therein, provided that  the  Board  of
          Directors  shall be of the opinion, after  consultation
          with counsel, that such changes or corrections will not
          be  prejudicial to the interests of the holders of  the
          Exchangeable Shares.


                           ARTICLE 11

                             LEGEND

11.1       The  certificates evidencing the  Exchangeable  Shares
shall  contain or have affixed thereto a legend, in form  and  on
terms  approved  by the Board of Directors, with respect  to  the
Support  Agreement,  the provisions of the  Plan  of  Arrangement
relating to the Retraction Call Right, the Liquidation Call Right
and  the Redemption Call Right, and the Voting and Exchange Trust
Agreement  (including the provisions with respect to  the  voting
rights, exchange right and automatic exchange thereunder).


                           ARTICLE 12

                            NOTICES

12.1       Any notice, request or other communication to be given
to the Corporation by a holder of Exchangeable Shares shall be in
writing  and  shall  be  valid and effective  if  given  by  mail
(postage prepaid) or by telecopy or by delivery to the registered
office  of the Corporation and addressed to the attention of  the
President.   Any such notice, request or other communication,  if
given by mail, telecopy or delivery, shall only be deemed to have
been  given  and  received upon actual  receipt  thereof  by  the
Corporation.

12.2            Any  presentation and surrender by  a  holder  of
Exchangeable Shares to the Corporation or the Transfer  Agent  of
certificates representing Exchangeable Shares in connection  with
the liquidation, dissolution or winding up of the Corporation  or
the retraction or redemption of Exchangeable Shares shall be made
by  registered  mail  (postage prepaid) or  by  delivery  to  the
registered  office of the Corporation or to such  office  of  the
Transfer  Agent as may be specified by the Corporation,  in  each
case  addressed  to  the  attention  of  the  President  of   the
Corporation.  Any such presentation and surrender of certificates
shall  only be deemed to have been made and to be effective  upon
actual  receipt thereof by the Corporation or the Transfer Agent,
as  the  case  may  be.  Any such presentation and  surrender  of
certificates made by registered mail shall be at the sole risk of
the holder mailing the same.

12.3       Any notice, request or other communication to be given
to  a  holder  of  Exchangeable Shares by or  on  behalf  of  the
Corporation shall be in writing and shall be valid and  effective
if  given by mail (postage prepaid) or by delivery to the address
of  the  holder  recorded  in  the  securities  register  of  the
Corporation  or, in the event of the address of any  such  holder
not  being  so recorded, then at the last known address  of  such
holder.   Any  such  notice, request or other  communication,  if
given by mail, shall be deemed to have been given and received on
the  fifth  Business Day following the date of  mailing  and,  if
given  by  delivery,  shall be deemed  to  have  been  given  and
received on the date of delivery.  Accidental failure or omission
to give any notice, request or other communication to one or more
holders  of Exchangeable Shares shall not invalidate or otherwise
alter  or  affect  any action or proceeding to be  taken  by  the
Corporation pursuant thereto.


      PROVISIONS ATTACHING TO THE CLASS B PREFERRED SHARES

           The  Class  B Preferred Shares in the capital  of  the
Corporation  shall  have attached thereto the  following  rights,
privileges, restrictions and conditions:

Dividends

           Subject  to  the prior rights of the  holders  of  the
Exchangeable  Shares and any other shares ranking senior  to  the
Class  B Preferred Shares with respect to priority in the payment
of  dividends, the holders of Class B Preferred Shares  shall  be
entitled  to  receive  dividends and the  Corporation  shall  pay
dividends  thereon,  as  and  when  declared  by  the  Board   of
Directors,  in  the amount of $0.10 per share per  annum  payable
quarterly on March 31, June 30, September 30 and December  31  in
each  year  (each  a "Dividend Payment Date") in  arrears.   Such
dividends shall be cumulative dividends and shall accrue from the
date  of issue, or from the most recent Dividend Payment Date  on
which dividends were paid, to and including the date to which the
computation of dividends is to be made.  A cheque for the  amount
of  the  dividend less any required deduction shall be mailed  by
first  class  mail  to  the addresses of the  registered  holders
thereof.

Redemption by the Corporation

           The Corporation may, upon giving notice as hereinafter
provided, redeem at any time the whole, but not a part  only,  of
the then outstanding Class B Preferred Shares on payment for each
share  to be redeemed of a sum of $1.00 together with all accrued
unpaid preferential cumulative cash dividends thereon whether  or
not declared (the "Redemption Amount").

           In  the case of redemption of Class B Preferred Shares
under  the  provisions  of the foregoing  paragraph  hereof,  the
Corporation shall at least 20 days before the date specified  for
redemption  mail to each person who at the date of mailing  is  a
registered  holder of Class B Preferred Shares to be  redeemed  a
notice  in writing of the intention of the Corporation to  redeem
such  Class B Preferred Shares.  Such notice shall be  mailed  by
letter,  postage prepaid, addressed to each such  shareholder  at
his  address  as  it appears on the records of  the  Corporation;
provided,  however,  that accidental failure  to  give  any  such
notice  to one or more of such shareholders shall not affect  the
validity  of  such  redemption.  Such notice shall  set  out  the
Redemption  Amount and the date on which redemption  is  to  take
place.   On  or  after the date so specified for redemption,  the
Corporation shall pay or cause to be paid to or to the  order  of
the  registered  holders of the Class B Preferred  Shares  to  be
redeemed  the  Redemption  Amount  thereof  on  presentation  and
surrender  of the certificates representing the Class B Preferred
Shares  called  for redemption at the registered  office  of  the
Corporation,  or  any  other place or places  designated  in  the
notice  of  redemption.   On and after  the  date  specified  for
redemption in any such notice the Class B Preferred Shares called
for  redemption shall cease to be entitled to dividends  and  the
holders  thereof  shall not be entitled to exercise  any  of  the
rights  of shareholders in respect thereof unless payment of  the
Redemption  Amount  shall  not  be  made  upon  presentation   of
certificates  in  accordance with the  foregoing  provisions,  in
which   case   the  rights  of  the  shareholders  shall   remain
unaffected.

           The Corporation shall have the right at any time after
the  mailing  of notice of its intention to redeem  any  Class  B
Preferred  Shares  as aforesaid to deposit the Redemption  Amount
for  the shares so called for redemption or for such of the  said
shares  represented by certificates as have not at  the  date  of
such   deposit  been  surrendered  by  the  holders  thereof   in
connection  with  such  redemption to  a  special  account  in  a
specified  chartered  bank in Canada, named  in  such  notice  of
redemption, to be paid without interest to or to the order of the
respective  holders of such Class B Preferred Shares  called  for
redemption  upon presentation and surrender to such bank  of  the
certificates  representing the same and upon such  deposit  being
made  or  upon the date specified for redemption in such  notice,
whichever  is the later, the Class B Preferred Shares in  respect
whereof such deposit shall have been made shall be deemed  to  be
redeemed  and the rights of the holders thereof shall be  limited
to  receiving without interest their proportionate  part  of  the
total  Redemption  Amount so deposited against  presentation  and
surrender  of  the  said certificates held by them  respectively.
Any  interest  allowed on any such deposit shall  belong  to  the
Corporation.  Redemption moneys that are represented by a  cheque
which  has  not been presented to the Corporation's  bankers  for
payment or that otherwise remain unclaimed (including moneys held
on  deposit  to a special account as provided for  above)  for  a
period of 6 years from the date specified for redemption shall be
forfeited to the Corporation.

Redemption at the Option of the Holders of the Class B  Preferred
Shares

           Every  registered holder of Class B  Preferred  Shares
may,  at  his  option  and  in the manner  hereinafter  provided,
require  the  Corporation to redeem at any time after  the  fifth
anniversary of the Effective Date all, but not part only, of  the
Class  B  Preferred Shares held by such holder upon  payment  for
each share to be redeemed of the Redemption Amount.

           In  the  case of the redemption of Class  B  Preferred
Shares under the provisions of this paragraph, the holder thereof
shall surrender the certificate or certificates representing such
Class  B  Preferred  Shares  at  the  registered  office  of  the
Corporation  accompanied  by  a notice  in  writing  (hereinafter
called a "redemption notice") signed by such holder requiring the
Corporation  to  redeem all, but not part only, of  the  Class  B
Preferred  Shares represented thereby.  As soon as is practicable
following  receipt of a redemption notice, the Corporation  shall
pay  or  cause  to be paid to or to the order of  the  registered
holder  of  the  Class  B Preferred Shares  to  be  redeemed  the
Redemption Amount thereof.

Dissolution

           In  the  event  of  the  dissolution,  liquidation  or
winding-up  of the Corporation, whether voluntary or involuntary,
or  any other distribution of assets of the Corporation among its
shareholders  for the purpose of winding up its affairs,  subject
to the prior rights of the holders of the Exchangeable Shares and
any  other shares ranking senior to the Class B Preferred  Shares
with  respect  to  priority in the distribution  of  assets  upon
dissolution, liquidation or winding-up, the holders of the  Class
B  Preferred Shares shall be entitled to receive an amount  equal
to  the  Redemption  Amount in respect of the Class  B  Preferred
Shares and any cumulative dividends remaining unpaid, whether  or
not  declared.   After  payment to the holders  of  the  Class  B
Preferred  Shares  of  such amounts, such holders  shall  not  be
entitled  to share in any further distribution of the  assets  of
the Corporation.

Voting Rights

           Except  where  specifically  provided  by  the  Canada
Business  Corporations Act, the holders of the Class B  Preferred
Shares  shall not be entitled to receive notice of or  to  attend
meetings of the shareholders of the Corporation and shall not  be
entitled  to  vote  at  any  meeting  of  shareholders   of   the
Corporation.


  PROVISIONS ATTACHING TO THE COMMON SHARES OF THE CORPORATION


           The  common  shares in the capital of the  Corporation
shall  have  attached  thereto the following rights,  privileges,
restrictions and conditions:

Dividends

           Subject  to  the prior rights of the  holders  of  the
Exchangeable Shares, the Class B Preferred Shares and  any  other
shares  ranking  senior  to the common  shares  with  respect  to
priority  in  the  payment of dividends, the  holders  of  common
shares shall be entitled to receive dividends and the Corporation
shall pay dividends thereon, as and when declared by the Board of
Directors  out  of moneys properly applicable to the  payment  of
dividends,  in  such  amount and in such form  as  the  Board  of
Directors may from time to time determine and all dividends which
the Board of Directors may declare on the common shares shall  be
declared and paid in equal amounts per share on all common shares
at the time outstanding.

Dissolution

           In  the  event  of  the  dissolution,  liquidation  or
winding-up  of the Corporation, whether voluntary or involuntary,
or  any other distribution of assets of the Corporation among its
shareholders  for the purpose of winding up its affairs,  subject
to  the  prior rights of the holders of the Exchangeable  Shares,
the  Class B Preferred Shares and any other shares ranking senior
to the common shares with respect to priority in the distribution
of  assets  upon  dissolution,  liquidation  or  winding-up,  the
holders  of  the common shares shall be entitled to  receive  the
remaining property and assets of the Corporation.

Voting Rights

           The holders of the common shares shall be entitled  to
receive  notice of and to attend all meetings of the shareholders
of  the Corporation and shall have one vote for each common share
held  at  all  meetings of the shareholders of  the  Corporation,
except  for  meetings at which only holders of another  specified
class or series of shares of the Corporation are entitled to vote
separately as a class or series.
                           SCHEDULE A

                      NOTICE OF RETRACTION


To  MacDonald  Dettwiler  Holdings Inc. (the  "Corporation")  and
Orbital Sciences Corporation ("Orbital")


           This  notice  is given pursuant to Article  5  of  the
provisions  (the  "Share Provisions") attaching to  the  share(s)
represented  by  this certificate and all capitalized  words  and
expressions  used in this notice that are defined  in  the  Share
Provisions  have  the  meanings  ascribed  to  such   words   and
expressions in such Share Provisions.

           The  undersigned hereby notifies the Corporation that,
subject  to  the  Retraction Call Right referred  to  below,  the
undersigned desires to have the Corporation redeem in  accordance
with Article 5 of the Share Provisions:


     all share(s) represented by this certificate; or


     _______________________ share(s) only.


           The undersigned acknowledges the Retraction Call Right
of  Orbital  to purchase all but not less than all the  Retracted
Shares  from the undersigned and that this notice shall be deemed
to  be an irrevocable offer (subject as hereinafter provided)  by
the  undersigned  to  sell the Retracted  Shares  to  Orbital  in
accordance with the Retraction Call Right on the Retraction  Date
for the Retraction Call Purchase Price and on the other terms and
conditions set out in section 5.1 of the Plan of Arrangement.  If
Orbital determines not to exercise the Retraction Call Right, the
Corporation will notify the undersigned of such fact as  soon  as
possible.

           The  undersigned acknowledges that if, as a result  of
solvency   provisions  of  applicable  law  or   otherwise,   the
Corporation fails to redeem all Retracted Shares, the undersigned
will  be  deemed to have exercised the Exchange Right (as defined
in  the  Voting  and Exchange Trust Agreement) so as  to  require
Orbital to purchase the unredeemed Retracted Shares.

           The undersigned hereby represents and warrants to  the
Corporation and Orbital:

                (i)  that the undersigned has good title to,  and
          owns,  the share(s) represented by this certificate  to
          be  acquired by the Corporation or Orbital, as the case
          may be, free and clear of all Liens; AND

               (ii) either


                                   the undersigned is a
                    resident of Canada for purposes  of
                    the Income Tax Act (Canada); OR

                                    the undersigned  is
                    not   a  resident  of  Canada   for
                    purposes  of  the  Income  Tax  Act
                    (Canada).



The  undersigned hereby acknowledges that, if the undersigned  is
not  a resident of Canada, and has not submitted with this notice
a  certificate issued by Revenue Canada under section 116 of  the
Income  Tax Act (Canada) in respect of the Retracted Shares,  the
amount of any securities or cash resulting from the retraction or
the  purchase  of  the Retracted Shares will be  reduced  by  the
amount  of  withholdings  required  under  the  Income  Tax   Act
(Canada).




____________________  ____________________   ____________________
____                  ______                 ____
       (Date)         (Signature of  Share   (Guarantee of Signat
                      holder)                ure)


     Please  check  box  if  the  securities  and  any  cheque(s)
     resulting  from the retraction or purchase of the  Retracted
     Shares are to be held for pick-up by the shareholder at  the
     principal  transfer  office  of Montreal  Trust  Company  of
     Canada   (the  "Transfer  Agent")  at  510  Burrard  Street,
     Vancouver,  British  Columbia, V6C  3B9  failing  which  the
     securities  and  any cheque(s) will be mailed  to  the  last
     address of the shareholder as it appears on the register.

NOTE:      This  panel  must  be completed and this  certificate,
     together  with  such additional documents  as  the  Transfer
     Agent may require, must be deposited with the Transfer Agent
     at   its  principal  transfer  office  in  Vancouver.    The
     securities  and any cheque(s) resulting from the  retraction
     or  purchase  of  the Retracted Shares will  be  issued  and
     registered in, and made payable to, respectively,  the  name
     of  the  shareholder as it appears on the  register  of  the
     Corporation and the securities and cheque(s) resulting  from
     such  retraction  or  purchase will  be  delivered  to  such
     shareholder  as  indicated above, unless the form  appearing
     immediately below is duly completed.




________________________________________  ______________________
________                                  _____
Name  of Person in Whose Name Securities  Date
or
Cheque(s)  Are To Be Registered,  Issued
or
Delivered (please print)

________________________________________  ______________________
________                                  _____
Street Address or P.O. Box                Signature            of
                                          Shareholder

________________________________________  ______________________
________                                  _____
City-Province                             Signature    Guaranteed
                                          by

NOTE:     If the notice of retraction is for less than all of the
     share(s)  represented  by  this certificate,  a  certificate
     representing the remaining shares of the Corporation will be
     issued and registered in the name of the shareholder  as  it
     appears on the register of the Corporation, unless the Share
     Transfer Power on the share certificate is duly completed in
     respect of such shares.