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                                                                   EXHIBIT 10.21

                            ASSET PURCHASE AGREEMENT

     Asset Purchase Agreement dated as of March  31, 1999 by and between
HyComp, Inc.  of 165 Cedar Hill Street, Marlborough, Massachusetts 01752 (the
'Seller') and HyComp Acquisition Corp., c/o SatCon Technology Corporation,  161
First Street, Cambridge, Massachusetts  02141 (the 'Purchaser'), with reference
to the following RECITALS:

     A.   Seller is in the business of manufacturing of hybrid circuits, thin
          film circuits and flip chip assembly;

     B.   Purchaser wishes to purchase certain equipment and other assets which
          are used by Seller in its business operations, and Seller desires to
          sell such assets.

NOW THEREFORE, in consideration of the recitals and of the respective covenants,
representations, warranties, and agreements herein contained, and intending to
be legally bound hereby, the parties hereby agree as follows:

     1.   PURCHASE AND SALE

          1.1.  Agreement to Sell.  At the Closing hereunder ( as defined in
                -----------------
Section 2.1) and except as specifically provided in Section 1.3, Seller shall
grant, sell, convey, assign, transfer and deliver to Purchaser, all right, title
and interest of Seller in and to (a) all of the tangible and intangible assets
of Seller including those more fully identified in Section 1.2, (b) the name
"HyComp" to the extent of the ownership rights of Seller, if any, and all of the
good will associated therewith; all of which shall be free and clear of all
mortgages, liens, pledges, security interests, charges, claims, restrictions and
encumbrances of any nature whatsoever (collectively the "Assets").

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          1.2  Included Assets. The Assets shall include, without limitation,
               ---------------
the following assets, properties and rights of the Seller, except as otherwise
set forth in Section 1.3 hereof.

          (a)  all machinery, equipment, tools, furniture, furnishings,
               leasehold improvements, goods and other tangible personal
               property owned by Seller, and shown on Schedule 1.2(a).

          (b)  all prepaid items as shown on Schedule 1.2(b).

          (c)  all supplies, raw materials, work in process, finished goods and
               other inventory as shown on Schedule 1.2(c).

          (d)  all right title, and interest of the Seller in and to all
               purchase orders as shown on Schedule 1.2(d).

          (e)  all of Seller's right, title and interest in and to the name
               "HyComp", to the extent of the ownership rights of Seller, if
               any, subject to the terms of Section 1.3(e) hereinafter;

          (f)  all rights under any trademark, service mark, trade name or
               copyright, whether registered or unregistered, and any
               applications therefore;

          (g)  all technologies, methods, formulations, data bases, trade
               secrets, know-how, inventions, and other intellectual property
               used in Seller's business or under development;

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          (h)  all information, files, records, data, plans, contracts and
               recorded knowledge including customer and supplier lists, related
               to the foregoing.

1.3  Excluded Assets.  Notwithstanding the foregoing the Assets shall not
     ---------------
include any of the following (the 'Excluded Assets'):

          (a)  the corporate seal, Articles of Organization, minute books, stock
               books, tax returns, books of account, accounting records or other
               records of Seller;

          (b)  any cash in any of Seller's bank accounts or in transit other
               than cash received by the Sellers on or after April 1, 1999 with
               respect to receivables that arise on and after April 1, 1999,
               which Seller shall remit to Buyer promptly after the receipt
               thereof in accordance with that certain letter executed today
               between Buyer and Seller;

          (c)  any accounts receivable of Seller as shown on Schedule 1.3(c)
               other than accounts receivables which arose on and after April 1,
               1999;

          (d)  any intercompany receivables of Seller as shown on Schedule
               1.3(d);

          (e)  the legal entity, public entity of HyComp, Inc. or its capital
               stock.

It is agreed that Seller, although selling the name "HyComp" herewith, may
continue to use the name "HyComp" in connection with the corporation HyComp,
Inc. so long as such corporation does not actively conduct business under such
name. At such time as Seller may dissolve its corporate entity it shall retain
no further right to the use of the name "HyComp".

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     1.4  Assumption of Liability.  At the Closing hereunder the Purchaser
          -----------------------
shall assume and agree to pay, discharge or perform, as appropriate,
the following liabilities and obligations the Seller (the "Assumed
Liabilities"):

     (a)  all liabilities and obligations of Seller identified on Schedule
1.4(a). All liabilities shall be paid promptly by Purchaser and
in all events within the period in which each liability is due.

     (b)  [Intentionally Omitted];

     (c)  all liabilities under the purchase orders set forth in
          Schedule 1.4(c);

     (d)  all taxes of Purchaser accruing subsequent to the Closing
          Date (as defined in Section 2.1);

          Purchaser shall not at the Closing assume or agree to perform, pay or
          discharge, and Seller shall remain unconditionally liable for, all
          obligations, liabilities and commitments, fixed or contingent, of
          Seller (including without limitation, intercompany accounts payable
          and notes payable to lenders), other than the Assumed Liabilities
          (such liabilities, obligations and commitments shall hereinafter be
          referred to as "Seller Liabilities").

     (e)  Liability under warranty for all rework and monetary payments to
          the extent that in the aggregate, for all such liabilities and
          payments shall be less than $25,000.00.

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1.5  Agreement to Purchase.  At the Closing, Purchaser shall purchase the
     ---------------------
Assets from Seller in exchange for the purchase price payable under Section 1.6
and the assumption of liabilities and obligations of Seller to the extent and as
provided in Section 1.4 of this Agreement.

1.6  Purchase Price. As consideration for the Assets, Purchaser shall deliver
     --------------
to Seller at the Closing:

          (a)  payment to the Seller of $750,000.00 by delivery of a certified
               check or by wire transfer completed and with funds immediately
               available as of the time of Closing (the 'Closing Payment');

          (b)  The Purchaser shall pay to Seller a royalty of 5% of all sales
               made to customers of Seller who are not also customers as of the
               Closing Date, of Purchaser ('Eligible Customers') for a period of
               52 weeks (the "Royalty Period") subsequent to the Closing date.
               The Eligible Customers are those identified on Schedule 1.6(b)
               annexed hereto. During the Royalty Period, Purchaser shall
               provide to Seller at least quarterly such records as Seller may
               reasonably require to account for all such sales to Eligible
               Customers. Payment shall be made by Purchaser to Seller after
               receipt of payment from Eligible Customers by Purchaser on a
               quarterly basis.

          (c)  Amounts identified on Schedule 1.4(a) to be paid at Closing,
               shall be paid at Closing.

1.7  [Intentionally Omitted]

1.8  Notification to Customers. Purchaser shall make timely notification in
     -------------------------
writing to all customers of Seller giving notice of Purchaser's purchase of

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assets pursuant to this agreement, such notification to be made no
later than two (2) weeks after the Date of Closing.

2.   Closing.
     -------

2.1  Time and Place of Closing. The closing (the "Closing") of the sale and
     -------------------------
purchase of the Assets shall take place at 12:00 P.M., Monday, April 12, 1999
(the "Closing Date") at the offices of Hale and Dorr LLP, 60 State Street,
Boston, Massachusetts 02109 or at such other time as may be mutually agreed upon
by Purchaser and Seller.

2.2  Items to be Delivered at Closing.
     --------------------------------

     (a)  Purchaser shall deliver to Seller:

          (i)   The Closing Payment;

          (ii)  A certificate of vote evidencing approval of the transactions
                contemplated herein; and

          (iii) Such other documents as Seller may reasonably require;

     (b)  Seller shall deliver to Purchaser:

          (i)   A bill of sale in customary form;

          (ii)  A certificate of vote evidencing approval of the transactions
                contemplated herein;

          (iii) Such legal opinions from Seller's counsel as Purchaser shall
                reasonably request; and

          (iv)  Such other documents as Purchaser may reasonably require.

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2.3  Delivery of Possession. At the Closing Seller shall put Purchaser in
     ----------------------
possession and operating control of the Assets, including but not limited to all
purchase orders, contracts, licenses, customer lists and all other documents,
books, records, files, data and property that are part of the Assets. Seller
shall execute and deliver such further documents and instruments as Purchaser
shall reasonably request from time to time in order to cause full possession and
control of the Assets to be transferred and delivered to Purchaser.

3.   REPRESENTATIONS AND WARRANTIES OF SELLER
     ----------------------------------------

     Seller represents and warrants to Purchaser as follows:

     3.1  Corporate Existence.  Seller is a corporation duly organized,
          -------------------
validly existing and in good standing under the laws of the Commonwealth of
Massachusetts.

     3.2  Corporate Power; Authorization; Enforceable Obligation. Seller
          ------------------------------------------------------
has the corporate power, authority and legal right to execute, deliver and
perform this Agreement. The execution, delivery and performance of this
Agreement by Seller have been duly authorized by all necessary corporate action.
This Agreement has been, and the other agreements, documents and instruments
required to be delivered by Seller in accordance with the provisions hereof
("Seller's Documents") will be, duly executed and delivered by Seller and this
Agreement constitutes, and Seller's Documents when executed and delivered will
constitute, the legal, valid and binding obligations of Seller, enforceable
against Seller in accordance with their respective terms.

     3.3  Validity of Contemplated Transactions, etc.   The execution,
          ------------------------------------------
delivery and performance of this Agreement by Seller and the consummation of the
transactions contemplated hereby, does not and will not violate, conflict with
or result in the breach of any term, condition or provision of, or require the

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consent of any other person under, (a) any existing law, ordinance, or
governmental rule or regulation to which Seller is subject, (b) any judgment,
order, writ, injunction, decree or award of any court, arbitrator or
governmental or regulatory official, body or authority which is applicable to
Seller, (c) the Articles of Organization and By-Laws, each as amended to date,
of, or any securities issued by Seller, or (d) any mortgage, indenture,
agreement, contract, commitment, lease, plan, permit license, or other
instrument, document or understanding , oral or written, to which Seller is a
party, by which Seller may have rights or by which any of the Assets may be
bound or affected, or give any party, by which Seller may have rights or by
which any of the Assets may be bound or affected, or give any party the right
thereunder the right to terminate, modify, accelerate, cancel or otherwise
change the existing rights or obligations of Seller thereunder. Except as
disclosed by Seller and agreed to by Purchaser on or before the Closing Date no
authorization, approval or consent of, and no resignation or filing with, any
governmental or regulatory official, body or authority is required in connection
with the execution, delivery or performance of this Agreement by Seller.

3.4. Financial Statements.
     --------------------

     (a)  Seller has also previously delivered to Purchaser its Current
          unaudited Balance Sheet for February 28, 1999, (the Current
          Financial Statement") attached as Schedule 3.4(a). The Current
          Financial Statement will be prepared in accordance with generally
          accepted accounting principles applied consistently with past
          practice, and have been certified by the Seller's comptroller in
          the case of the Current Financial Statements.

     (b)  The Financial Statements for February and March fairly present,
          as of their respective dates, the financial condition of assets
          and liabilities of Seller; with respect to the contracts and
          commitments

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            for the sale of goods or the provision of services by Seller, the
            Financial Statements contain and reflect adequate reserves, which
            are consistent with previous reserves taken, for all reasonably
            anticipated material losses and costs and expenses.

3.5  Absence of Undisclosed Liabilities.  Except as and to the extent
     ----------------------------------
(a) reflected and reserved in the Current Balance Sheet, (b) set forth on
Schedule 3.5 attached hereto or (c) incurred in the ordinary course of business
after the date of the Current Balance Sheet and not material in amount, either
individually or in the aggregate, Seller does not have any liability or
obligation, secured or unsecured, whether accrued, absolute, contingent,
unasserted or otherwise, affecting the Assets. For purposes of this Section 3.5
"material" means any amount in excess of $75,000.00.

3.6  Contracts and Commitments.
     -------------------------

             (a) Schedule 3.6 annexed hereto contains complete and correct list
                 and description of the following contracts and agreements,
                 whether written or oral (collectively, the "Contracts"):

       (i)   Delete

       (ii)  all pledges, conditional sale or title retention
             agreements, security agreements, equipment obligations,
             personal property leases and lease purchase agreements
             relating to any of the Assets to which Seller is a party or
             by which Seller or any of its property is bound.

       (iii) all contracts, agreements, commitments, purchase orders or
             other understandings or arrangements to which Seller is a
             party or by which Seller or any of its property is bound
             which (A) involve payments or receipts by Seller of more
             than $5,000.00 in the case

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                      of any single contract, agreement, commitment,
                      understanding or arrangement under which full performance
                      (including payment) has not been rendered by all parties
                      thereto or (B) which may materially adversely affect the
                      condition (financial or otherwise) or the properties,
                      assets, business or prospects of Seller;

               (iv)   Delete

               (v)    all agency, distributor, sales representative and similar
                      agreement to which Seller is a party;

               (vi)   Delete

               (vii)  all leases, whether operating, capital or otherwise, under
                      which Seller is lessor or lessee;

               (viii) any other material agreement or contract entered into by
                      Seller, including without limitation, the purchase orders
                      which have been committed to or accepted by Seller.

          (b)  Except as set forth on Schedule 3.6(b) annexed hereto:

               (i)    each Contract is a valid and binding agreement of Seller,
                      enforceable against Seller in accordance with its terms,
                      and Seller does not have any knowledge that any Contract
                      is not a valid and binding agreement of the other parties
                      thereto;

               (ii)   Delete

               (iii)  Seller is not in breach of or default under any Contract,
                      and no event has occurred which with the passage of time
                      or giving of

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                notice or both would constitute such a default, result in a
                loss of rights or result in the creation of any lien,
                charge or encumbrance, thereunder or pursuant thereto;

          (iv)  to the best knowledge of Seller, there is no existing
                breach or default by any other party to any Contract, and
                no event has occurred which with the passage of time or
                giving of notice or both would constitute a default by such
                other party, result in a loss of rights or result in the
                creation of any lien, charge or encumbrance thereunder or
                pursuant thereto;

          (v)   Seller is not restricted by any Contract except by
                government regulation as part of military specifications
                under which certain products are manufactured from carrying
                on its business anywhere in the world; and

          (vi)  Delete

     (c)  Delete

     (d)  True, correct and complete copies of all Contracts have
          previously been delivered by Seller to Purchaser.

3.7  Compliance with Agreements of Laws. Seller has all requisite licenses,
     ----------------------------------
permits, and certificates, including environmental, health and safety permits,
from federal, state and local authorities necessary to conduct its business and
own and operate its assets (collectively, the "Permits"). Schedule 3.7 annexed
hereto sets forth a true, correct and complete list of all such Permits, copies
of which have previously been delivered by Seller to Purchaser. All Permits
shall inure to the benefit of Purchaser immediately following the Closing
without the requirement of obtaining any consent, giving Purchaser the same
rights as Seller immediately prior to the Closing.

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<PAGE>

Except as set forth on Schedule 3.7 annexed hereto, Seller has not since
January 1, 1996 received any notice or communication from any federal, state or
local governmental or regulatory authority or otherwise of any such violation or
noncompliance.

3.8  Delete

3.9  Disclaimer of All Other Warranties.  EXCEPT AS SET FORTH IN  SECTIONS 3.1
     ----------------------------------
THROUGH 3.7 HEREOF, THE ASSETS ACQUIRED BY PURCHASER HEREUNDER ARE BEING SOLD
"AS IS" AND "WHERE IS" WITH ALL FAULTS THAT MAY EXIST THEREIN. SELLER DISCLAIMS
ANY WARRANTY OF ANY OTHER KIND, INCLUDING ANY WARRANTY THAT THE ASSETS ARE FIT
FOR A PARTICULAR PURPOSE.

3.10 Security Clearance.   Seller received a Facility Security Clearance for
     ------------------
165 Cedar Hill Street, Marlborough, Massachusetts 01752 dated July 24, 1998 from
the Defense Investigating Service. This clearance is due to expire on July 23,
1999.

4.   REPRESENTATIONS AND WARRANTIES OF PURCHASER.
     -------------------------------------------
     Purchaser represents and warrants to Seller as follows:

4.1  Corporate Existence. Purchaser is a corporation duly organized, validly
     -------------------
existing and in good standing under the laws of the State of Delaware.

4.2  Corporate Power; Authorization; Enforceable Obligations. Purchaser has
     --------------------------------------------------------
the corporate power, authority and legal right to execute, deliver and perform
this Agreement. The execution, delivery and performance of this Agreement by
Purchaser has been duly authorized by all necessary corporate action. This
Agreement has been, and the other agreements, documents and instruments required
to be delivered by Purchaser in accordance with the provisions hereof
("Purchaser's Documents") will be, duly executed and delivered by Purchaser, and
this Agreement constitutes, and

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<PAGE>

Purchaser's Documents when executed and delivered will constitute, the legal,
valid and binding obligations of Purchaser; enforceable against Purchaser in
accordance with their respective terms.

4.3  Purchaser Objective. The Purchaser acknowledges that it is aware and has
     --------------------
knowledge that shipments and backlog of business of the Seller has declined in
volume and that Seller shall have no liability arising from the sales or backlog
decline.

4.4.  No Reliance. Purchaser represents that it has conducted its own due
      ------------
diligence and it is relying solely upon such due diligence with which it is
satisfied and it is not relying upon any representations of  Seller other than
the representations contained herein.

5.   CONDITIONS PRECEDENT TO THE CLOSING.
     -----------------------------------

5.1  Lease Obligations. This Agreement is subject to Purchaser executing with
     ------------------
Seller's current landlord (the "Landlord"), on or before the Closing Date, a new
lease agreement for the period from the Closing Date to the end of the period of
Seller's present lease and an additional period of five (5) years thereafter,
for the premises located at 165 Cedar. Hill Street, Marlborough, Massachusetts
01752, and that Seller shall have no obligation to the Landlord during any term
of Purchaser's lease or extensions thereof as a result of Purchasers actions or
omissions post closing.

5.2  Employment Contract of George Riley. This Purchase Agreement is subject to
     ------------------------------------
the Purchaser executing with George Riley, on or before the Closing Date, an
employment contract on terms mutually agreeable to the Purchaser and to George
Riley. Further, it is a condition of this Agreement that the Purchaser assumes
all liability with respect to all employment benefits and obligations due to
George Riley and annexed hereto on Schedule 5.2.

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5.3  Conditions to Obligations of Seller.  The obligations of Seller
     ------------------------------------
to consummate the transactions contemplated by this Agreement are subject to the
satisfaction, on or before the Closing Date, of the following conditions:

         (a)   Representations and Warranties. The representations and
               -------------------------------
     warranties of Purchaser set forth in this Agreement shall be true and
     correct in all material respects as of the date of this Agreement and as of
     the Closing Date as though made on and as of the Closing Date.

         (b)   Performance by the Purchaser.  On or before Closing Date,
               ----------------------------
     Purchaser shall have performed and complied with all agreements and
     conditions required by this Agreement.

         (c)   Form and Content of Documents. The form and content of all
               ------------------------------
     documents, certificates and other instruments to be delivered by Purchaser
     shall be reasonably satisfactory to Seller.

         (d)   Litigation Affecting Closing.  No court order shall have
               -----------------------------
     been issued or entered which would be violated by the consummation of the
     transactions contemplated by this Agreement. No person or entity shall have
     commenced or threatened to commence any litigation seeking to restrain or
     prohibit, or to obtain substantial damages in connection with this
     Agreement or the transactions contemplated by this Agreement.

         (e)   Purchase Price.  Seller shall have received the Closing
               ---------------
     Payment constituting the purchase price for the Assets.

     5.4  Conditions to Obligations of Purchaser.  The obligations of
          ---------------------------------------
     Purchaser to consummate the transactions contemplated by this Agreement are
     subject to the satisfaction on or before the Closing Date of the following
     conditions.

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<PAGE>

     (a)   Representations and Warranties. The representations and
           -------------------------------
warranties of Seller set forth in this Agreement shall be true and correct in
all material respects as of the date of this Agreement and as of the Closing
Date as though made on and as of the Closing Date.

     (b)   Performance by Seller.  Seller shall have performed and
           ----------------------
complied with all agreements and conditions required by this Agreement.

     (c)   No Threatened or Pending Litigation.  On or before the Closing Date,
           ------------------------------------
no suit, action or other proceeding, or injunction or final judgment relating
thereto, shall be threatened or pending before any court or governmental or
regulatory official, body or authority in which it is sought to restrain or
prohibit or to obtain damages or other relief in connection with this Agreement
or the consummation of the transactions contemplated hereby, and no
investigation that might result in any such suit, action or proceeding shall be
pending or threatened.

     (d)   Delete

     (e)   Form and Content Documents.  The form and content of all
           ---------------------------
documents, certificates and other instruments to be delivered by Seller shall
be reasonably satisfactory to Purchaser.

     (b)   The transactions contemplated by this Agreement shall have
been approved by all necessary corporate and stockholder action by Seller.

6.   NON COMPETITION.  Seller on behalf of itself and its affiliates
     ----------------
agrees that neither Seller nor its affiliates will for a period of five (5)
years from the Closing Date either directly or indirectly engage in the hybrid
circuit business,

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<PAGE>

the thin film circuit business or the flip chip assembly business, each of which
are businesses in which Seller is presently engaged.

7.   TAXES.  Seller will, on a timely basis, file all tax returns for and
     -----
pay any and all taxes which shall become due or shall have accrued (i ) on
account of the operation of the business of Seller or the ownership of the
Assets during the period on or before the Closing Date or (ii) on account of the
sale of the Assets (including a pro-rata portion of all personal property and
excise taxes payable with respect to the Assets of Seller).

8.   UNITED STATES GOVERNMENT PROPERTY.  Purchaser acknowledges that certain
     ---------------------------------
equipment upon Seller's premises is the property of the United States
Government. Such equipment is listed on Schedule 8 annexed hereto. At Closing
Seller shall transfer all such property to the possession of Purchaser. However,
Seller makes no representation with regard to the final disposition of said
property including but not limited to the length of time it will remain in the
possession of Purchaser.

9.   INDEMNIFICATION.
     ---------------

     9.1  Seller hereby indemnifies and holds harmless Purchaser and its
          affiliates and their respective officers, directors, employees and
          agents against all claims, damages, losses, liabilities, costs and
          expenses (including, without limitation, settlement costs and any
          legal, accounting or other expenses for investigating or defending any
          actions or threatened actions) reasonably incurred by such persons in
          connection with each and all of the following:

          (a)  Any breach by Seller of any representation or warranty in this
               Agreement;

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<PAGE>

          (b)  Any breach of any covenant, agreement or obligation of Seller
               contained in this Agreement or any other agreement, instrument or
               document contemplated by this Agreement;
          (c)  Any liability or obligation relating to a Seller Liability or
               otherwise relating to an Excluded Asset;

          (d)  Any violation by Seller of, or any failure by Seller to comply
               with, any law, ruling, order, decree, regulation or zoning,
               environmental or permit requirement applicable to Seller, the
               Assets or its business, whether or not any such violation or
               failure to comply has been disclosed to Purchaser.

          (e)  The failure of Purchaser to obtain the protections afforded by
               compliance with the notification and other requirements of the
               bulk sales laws in force in the jurisdictions in which such laws
               may be applicable to either Seller or the transaction
               contemplated by this Agreement;

          (f)  Any warranty claim or product liability claim relating to (I)
               products manufactured or sold by Seller prior to the Closing Date
               to the extent resulting in costs, expenses or liabilities to
               Purchases in the aggregate in excess of $25,000.

          (g)  Any tax liabilities or obligations of Seller;

          (h)  Any mortgage, lien, pledge, security interest, charge, claim,
               restriction or encumbrance of any nature whatsoever effecting or
               encumbering the Assets; and

                                                                              17
<PAGE>

               (i)  Any failure of Seller to comply with any applicable federal
                    or state securities laws or applicable laws relating to
                    shareholder appraisal rights.

          9.2  By Purchaser.  Purchaser hereby indemnifies and holds harmless
               ------------
Seller and its affiliates and their respective officers, directors, employees
and agents from any and all claims, damages, losses, liabilities, costs and
expenses (including, without limitation, settlement costs and any legal,
accounting or other expenses for investigating or defending any actions or
threatened actions) reasonably incurred by such persons, in connection with each
and all of the follows:

          (a)  Any breach by Purchaser of any representation or warranty in this
               Agreement;
          (b)  Any breach of any covenant, agreement or obligation of Purchaser
               contained in this Agreement or in any other agreement, instrument
               or document contemplated by this Agreement;

          (c)  Any Assumed Liability; and

          (d)  Any liability relating to the operation of the business purchased
               by Purchaser pursuant to this Agreement first arising after the
               Closing Date (other than a liability resulting from a breach of a
               representation by Seller or with respect to which Purchaser is
               indemnified pursuant to Section 9.1 of this Agreement.

          (e)  Any liabilities arising out of the operation of the business by
               Purchaser first occurring on or after the Closing Date relating
               to any claims of vendors of Seller and any claims of Employees of
               Seller who are hired by Purchaser.

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<PAGE>

9.3  Claims for Indemnification. Whenever any claim shall arise for
     --------------------------
indemnification hereunder the party seeking indemnification (the "Indemnified
Party"), shall promptly notify the party from whom indemnification is sought
(the "Indemnifying Party") of the claim and, when known, the facts constituting
the basis for such claim.  In the event of any such claim for indemnification
hereunder resulting from or in connection with any claim or legal proceedings by
a third-party, the notice to the Indemnifying Party shall specify, if known, the
amount or an estimate of the amount of the liability arising therefrom.  The
Indemnified Party shall not settle or compromise any claim by a third party for
which it is entitled to Indemnification hereunder without the prior written
consent of the Indemnifying Party, which shall not be unreasonably withheld,
unless suit shall have been instituted against it and the Indemnifying Party
shall not have taken control of such suit after notification thereof as provided
in Section 9.4 of this Agreement.

9.4  Defense of Indemnifying Party. In connection with any claim giving rise
     -----------------------------
to indemnity hereunder resulting from or arising out of any claim or legal
preceding by a person who is not a party to this Agreement the Indemnifying
Party at its sole cost and expense may, upon written notice to the Indemnified
Party, assume the defense of any such claim or legal proceeding if it
acknowledges to the Indemnified Party in writing its obligations to indemnify
the Indemnified Party with respect to all elements of such claim. The
Indemnified Party shall be entitled to participate in (but not control) the
defense of any such action, with its counsel and at its own expense. If the
Indemnifying Party does not assume the defense of any such claim or litigation
resulting therefrom within thirty (30) days after the date such claims is made,
(a) the Indemnified Party may defend against such claim or litigation, in such
manner as it may deem appropriate, including, but not limited to, settling such
claim or litigation, after giving notice of the same to the Indemnifying Party,
on such terms as the Indemnified Party may deem appropriate, and (b) the
Indemnifying Party shall be entitled to participate in (but not control) the
defense of such action, with its counsel and at its own expense. If the
indemnifying Party thereafter seeks to question the manner in which the
Indemnified Party defended such third party claim or the amount or nature of any
such settlement, the Indemnifying Party

                                                                              19
<PAGE>

shall have the burden to prove by a preponderance of the evidence that the
Indemnified Party did not defend or settle such third party claim in a
reasonably prudent manner.

9.5  Payment of Indemnification Obligation. All indemnification by Purchaser or
     -------------------------------------
Seller hereunder shall be effected by payment of cash or delivery of a cashier's
or certified check in the amount of the indemnification liability.

9.6  Survival of Representations; Claims for Indemnification. All
     -------------------------------------------------------
representations and warranties made by the parties herein or in any instrument
or document furnished in connection herewith shall survive the Closing and any
investigation at any time made by or on behalf of the parties hereto.  All
claims for indemnification relating to a breach of a representation or warranty
shall be asserted prior to the end of the twelve month period commencing on the
Closing Date.

10.  SELLER'S EMPLOYEES.  As of the Closing Date, Purchaser shall offer
     ------------------
employment to the employees of Seller listed on Schedule 10 annexed hereto.  As
of the Closing Date, all employees who are employed by Purchaser shall no longer
be considered employees of Seller for any purposes.

11.  MISCELLANEOUS.
     -------------

     11.1  Amendment. This Agreement may only be amended by an instrument
           ---------
     in writing signed on behalf of each of the parties hereto.

     11.2  Extension Waiver.  At any time prior to the Closing the parties
           ----------------
     hereto may extend the time for the performance of any of the obligations or
     other acts of the other parties hereto, waive any inaccuracies in the
     representations and warranties contained herein or in any document
     delivered pursuant hereto and waive compliance with any of the agreements
     or conditions contained herein. Any agreement on the part of a party hereto
     to any such extension or

                                                                              20
<PAGE>

      waiver shall be valid only if set forth in a written instrument signed on
      behalf of both parties.

      11.3  Counterparts.  This Agreement may be executed in two or more
            ------------
      counterparts, all of which shall be considered one and the same agreement
      and shall become effective when two or more counterparts have been signed
      by each of the parties and delivered to the other parties, it being
      understood that all parties need not sign the same counterpart.

      11.4  Governing Law.  This Agreement shall be governed and construed
            -------------
      in accordance with the laws of the Commonwealth of Massachusetts. Each
      party hereby irrevocably submits to the jurisdiction of the Superior Court
      of the Commonwealth in respect of any suit, action or proceeding arising
      out of this Agreement, and irrevocably accepts for themselves for and in
      respect of their property, generally and unconditionally, the jurisdiction
      of the aforesaid court.


11.5  Notice.  Any notice, request, demand, waiver, consent, approval
      ------
or other communication which is required or permitted hereunder shall be in
writing and shall be deemed given only if delivered personally or sent by
registered or certified mail, postage prepaid, as follows:

               If to Seller, to:

               HyComp, Inc.
               C/o XIT Corporation
               4290 East Brickell St.
               Ontario, California 91761-1511
               Attention: Carmine T. Oliva

                                                                              21
<PAGE>

                 With a required copy to:
                 Gaffin & Waldstein
                 P.O. Box 886
                 1101 Worcester Rd.
                 Framingham, Massachusetts 01701
                 Attention:  Thomas G. Waldstein, Esq.


                 If to Purchaser to:
                 HyComp Acquisition Corp.
                 c/o SatCon Technology Corporation
                 161 First Street
                 Cambridge, Massachusetts 02142


                 [Remainder of Page Intentionally Left Blank]

                                                                              22
<PAGE>

          Attention:  David B. Eisenhaure

               With a required copy to:
               Hale and Dorr LLP
               60 State Street
               Boston, Massachusetts 02109
               Attention:  Jeffrey N. Carp, Esq.

or to such other address as the addressee may have specified in a notice duly
given to the sender as provided herein.

11.6  Assignment and Binding Effect.  This Agreement may not be assigned prior
      ------------------------------
to the Closing by any party hereto without the prior written consent of the
other parties. Subject to the foregoing, all of the terms and provision of this
Agreement shall be binding upon and inure to the benefit of and be enforceable
by the successors and assigns of Seller and Purchaser.

11.7  Brokers and Finders Fees. Seller, on the one hand, and Purchaser, on the
      -------------------------
other hand, each to the other represent and warrant that any and all broker's or
investment banker's fees due and payable as a result of this Agreement shall be
the sole and exclusive responsibility of the party who has engaged such broker
or investment banker on its behalf.

11.8  Severability. Any provision of this Agreement which is invalid
      -------------
or unenforceable in any jurisdiction shall be ineffective to the extent of such
invalidity or unenforceability without invalidating or rendering unenforceable
the remaining provisions hereof, and any such invalidity or unenforceability in
any jurisdiction shall not invalidate or render unenforceable such provision in
any other jurisdiction.

IN WITNESS WHEREOF, the parties hereto have duly executed this Agreement under
seal as of the date set forth above.

                                                                              23
<PAGE>

                                 HyComp, Inc.


                             By: /s/ Carmine T. Oliva
                                 --------------------------------
                                 Carmine T. Oliva
                                 Chairman and CEO


                                 HyComp Acquisition Corp.


                             By: /s/ David B. Eisenhaure
                                 --------------------------------
                                 David B. Eisenhaure
                                 President and CEO

                                                                              24
<PAGE>

                               Omitted Schedules
                               -----------------

     Pursuant to Item 601(b)(2) of Regulation S-K promulgated by the Securities
and Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended, and the Securities Exchange Act of 1934, as amended, SatCon Technology
Corporation has, with respect to the Asset Purchase Agreement by and between
HyComp, Inc. and HyComp Acquisition Corp., dated as of March 31, 1999, omitted
to file the related schedules (listed below). These schedules will be
supplementally furnished to the Commission upon request.


                                   Schedules

     1.2a       Machinery and Equipment
     1.2b       Prepaid Items
     1.2c       Inventory
     1.2d       Purchase Orders
     1.3c       Accounts Receivable
     1.3d       Intercompany Receivables
     1.4a       February Balance Sheet
     1.4c       Liabilities Under Purchase Orders
     1.6b       Eligible Customers for Royalty
     1.6c.i.    Employee Severance
          ii.   Vacation Pay
          iii.  J. Madden Bonus
          iv.   C. O'Connell Reimbursement
          v.    Seller Expenses from March 31 to Closing
     1.7        Allocation of Purchase Price
     3.6a.ii.   Pledges on Assets
        a.iii.  Contracts, Commitments, Purchase Orders

                                                                              25
<PAGE>

         a.v.   Distributors/Sales Representatives
         a.vii. Leases
     3.6b       Exceptions re: contracts
     3.7        Permits
     5.2        G. Riley Benefits and Obligations
     8          United States Government Property
     10         Purchaser  Employees Hired

                                                                              26