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                                                                     EXHIBIT 4.8

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                             XM Satellite Radio Inc.

                   14% SENIOR SECURED DISCOUNT NOTES DUE 2009

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                          FIRST SUPPLEMENTAL INDENTURE

                               Dated June 12, 2003

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                              The Bank of New York

                                     Trustee

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     FIRST SUPPLEMENTAL INDENTURE, dated as of June 12, 2003, by and among XM
Satellite Radio Inc., a Delaware corporation (the "Company"), XM Satellite Radio
Holdings Inc., a Delaware corporation (the "Parent Guarantor"), XM Equipment
Leasing LLC, a Delaware limited liability company, and each of the other
Subsidiary Guarantors made a party to the Indenture pursuant to Section 11.05
thereof, and The Bank of New York, as trustee (the "Trustee").

                                   WITNESSETH

     WHEREAS the Company has executed and delivered to the Trustee an Indenture
dated as of January 28, 2003 (as amended and supplemented, the "Indenture"),
providing for the issuance of 14% Senior Secured Discount Notes due 2009 (the
"Notes");

     WHEREAS, the General Security Agreement contains certain ambiguities which
the Company proposes to clarify through an amendment in the form attached hereto
as EXHIBIT A (the "Amendment"), which clarifications are beneficial to, and do
not adversely affect the legal rights of, the Holders of the Notes;

     WHEREAS, Section 9.01 of the Indenture provides, among other things, that
the Company, the Parent Guarantor, the Subsidiary Guarantors and the Trustee may
supplement the Indenture without the consent of any Holder of a Note to make any
change that would provide any additional rights or benefits to the Holders of
the Notes or that does not adversely affect the legal rights of any Holder of a
Note;

     WHEREAS, this First Supplemental Indenture has been duly authorized by all
necessary corporate action on the part of the Company and the Company has
delivered, or caused to be delivered, to the Trustee an Officers' Certificate
and an Opinion of Counsel meeting the requirements of Sections 7.02, 9.06, 13.04
and 13.05 of the Indenture and stating that the execution and delivery of this
First Supplemental Indenture is permitted by the Indenture and that all
conditions precedent (including any covenants compliance with which constitutes
a condition precedent), if any, provided for in the Indenture relating to this
First Supplemental Indenture have been satisfied;

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, receipt of which is hereby acknowledged, the Company,
the Parent Guarantor, the Subsidiary Guarantors and the Trustee mutually
covenant and agree for the equal and ratable benefit of the Holders of the Notes
as follows:

                                    ARTICLE I

                              ACTION BY THE TRUSTEE

     SECTION 1.01. AMENDMENT OF THE SECURITY AGREEMENT. In accordance with
Sections 9.01 and 9.06 of the Indenture, the Trustee shall (i) execute and
deliver, on behalf of the Holders, the Consent in the form attached hereto, (ii)
direct the Collateral Agent to execute and deliver the Amendment in the form
attached hereto and (iii) execute and deliver all other

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documents or take such other actions, or direct the Collateral Agent to execute
and deliver all other documents or take such other actions, as may be necessary
or appropriate to consummate the transactions contemplated hereby.

                                   ARTICLE II

                                  MISCELLANEOUS

     SECTION 2.01. SUPPLEMENTAL INDENTURES PART OF INDENTURE. Upon the execution
and delivery of this First Supplemental Indenture by the Company, the Parent
Guarantor, the Subsidiary Guarantors and the Trustee, this First Supplemental
Indenture shall form a part of the Indenture for all purposes, and every holder
of Notes heretofore or hereafter authenticated and delivered shall be bound
hereby. Any and all references, whether within the Indenture or in any notice,
certificate or other instrument or document, shall be deemed to include a
reference to this First Supplemental Indenture (whether or not made), unless the
context shall otherwise require.

     SECTION 2.02. GOVERNING LAW; GOVERNANCE, ETC. THIS FIRST SUPPLEMENTAL
INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF
THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF
CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER
JURISDICTION WOULD BE REQUIRED THEREBY. This First Supplemental Indenture shall
be governed and construed in accordance with the applicable terms and provisions
of the Indenture as supplemented hereby, which terms and provisions are
incorporated herein by reference, as if this First Supplemental Indenture were
the "Indenture" referred to therein.

     SECTION 2.03. TRUSTEE ACCEPTANCE. The Trustee accepts the Indenture, as
supplemented hereby, and agrees to perform the same upon the terms and
conditions set forth therein, as supplemented hereby. The recitals contained
herein shall be taken as the statements of the Company, the Parent Guarantor and
the Subsidiary Guarantors, and the Trustee assumes no responsibility for their
correctness. The Trustee makes no representation as to the validity or
sufficiency of this First Supplemental Indenture.

     SECTION 2.04. COUNTERPARTS. The parties may sign any number of copies of
this First Supplemental Indenture. Each signed copy shall be an original, but
all of them together represent the same agreement.

     SECTION 2.05. EFFECT OF HEADINGS. The Section headings herein are for
convenience only and shall not affect the construction thereof.

     SECTION 2.06. TERMS. Capitalized terms used but not defined herein have the
meanings assigned to them in the Indenture.

     SECTION 2.07. BENEFITS OF FIRST SUPPLEMENTAL INDENTURE. Nothing in this
First Supplemental Indenture, the Indenture, or the Notes, express or implied,
shall give to any Person, other than the parties hereto and thereto and their
successors hereunder and thereunder, and the

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Holders, any benefit of any legal or equitable right, remedy or claim under the
Indenture, the First Supplemental Indenture or the Notes.

     SECTION 2.08. EFFECTIVENESS OF FIRST SUPPLEMENTAL INDENTURE.
Notwithstanding anything to the contrary contained herein, this First
Supplemental Indenture shall become effective on the date hereof.

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     IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental
Indenture to be duly executed as of the date first above written.

                                   XM Satellite Radio Inc.

                                   By: /s/ Joseph M. Titlebaum
                                       -----------------------
                                       Joseph M. Titlebaum
                                       Executive Vice President, General Counsel
                                       and Secretary
Attest:

/s/ Gary M. Parsons
Name: Gary M. Parsons
Title: Chairman

                                   XM Satellite Radio Holdings Inc.,
                                   as Parent Guarantor

                                   By: /s/ Joseph M. Titlebaum
                                       Joseph M. Titlebaum
                                       Executive Vice President, General Counsel
                                       and Secretary
Attest:

/s/ Gary M. Parsons
Name: Gary M. Parsons
Title: Chairman

                                   XM Equipment Leasing LLC,
                                   as Subsidiary Guarantor

                                   By: /s/ Joseph M. Titlebaum
                                       Joseph M. Titlebaum
                                       Executive Vice President, General Counsel
                                       and Secretary
Attest:

/s/ Gary M. Parsons
Name: Gary M. Parsons
Title: Chairman

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                                   The Bank of New York

                                   By: /s/ John Guiliano
                                       Name: John Guiliano
                                       Title: Vice President
Attest:

/s/ Joseph A. Llovet
Name: Joseph A. Llovet
Title: Assistant Treasurer

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                                    EXHIBIT A

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                                                                     EXHIBIT 4.9

                                 FIRST AMENDMENT
                              TO SECURITY AGREEMENT

          THIS FIRST AMENDMENT TO SECURITY AGREEMENT (this "AMENDMENT") dated as
of June 12, 2003, among XM Satellite Radio Inc., a Delaware corporation
("COMPANY"), XM Satellite Radio Holdings Inc., a Delaware corporation,
("HOLDINGS"), XM Equipment Leasing LLC, a Delaware limited liability company
("XM LEASING SUBSIDIARY") and The Bank of New York, acting as collateral agent
("COLLATERAL AGENT").

                                   WITNESSETH

          WHEREAS, the Company, Holdings, XM Leasing Subsidiary and the
Collateral Agent are parties to that certain Security Agreement, dated as of
January 28, 2003 (as amended by this Amendment, the "SECURITY AGREEMENT").
Capitalized terms not otherwise defined in this Amendment have the same meanings
as specified in the Security Agreement;

          WHEREAS, the Company, Holdings, XM Leasing Subsidiary and the
Collateral Agent have agreed to amend the Security Agreement as set forth
herein; and

          WHEREAS, the Collateral Agent has been instructed by the Required
Secured Parties under the Intercreditor Agreement to enter into this Amendment;

          NOW, THEREFORE, subject to the terms and conditions set forth below,
it is agreed:

       1.   Paragraph G of the Recitals of the Security Agreement is hereby
amended by:

               A. inserting the word "Agreement" before the phrase "(General
                  Security Agreement)" and

               B. deleting the phrase "New Secured Parties" and substituting in
                  lieu thereof the phrase "Additional Creditors".

       2.   Section 3.1 of the Security Agreement is hereby amended by:

               A. deleting the phrase "Grantor is a party, and for all" and
                  substituting in lieu thereof the phrase "Grantor is a party
                  and all" and

               B. inserting the phrase "of such Grantor" immediately before the
                  phrase "(the "SECURED OBLIGATIONS")".

       3.   This Amendment shall be effective on the date hereof.

       4.   This Amendment is limited as specified and shall not constitute a
modification, acceptance or waiver of any other provision of the Security
Agreement.

AMENDMENT NO. 1 TO SECURITY AGREEMENT

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       5.   This Amendment may be executed in any number of counterparts and by
the different parties hereto on separate counterparts, each of which
counterparts when executed and delivered shall be an original, but all of which
shall together constitute one and the same instrument.

       6.   This Amendment shall be governed by, and construed in accordance
with, the laws of the State of New York, without giving effect to any conflicts
of laws principles thereof other than New York General Obligations Law Sections
5-1401 and 5-1402.

       7.   From and after the date hereof, all references in the Security
Agreement to "this Agreement," "hereunder," "hereof" or words of like import
referring to the Security Agreement shall be deemed to be references to the
Security Agreement as modified hereby.

AMENDMENT NO. 1 TO SECURITY AGREEMENT

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IN WITNESS WHEREOF, Grantors and Collateral Agent have caused this Amendment to
be duly executed and delivered by their respective officers thereunto duly
authorized as of the date first written above.

                            XM SATELLITE RADIO INC.

                            By:    /s/ Joseph M. Titlebaum
                                ------------------------------------
                                   Joseph M. Titlebaum
                                   Executive Vice President, General Counsel
                                   and Secretary

                            XM SATELLITE RADIO HOLDINGS INC.

                            By:    /s/ Joseph M. Titlebaum
                                ------------------------------------
                                   Joseph M. Titlebaum
                                   Executive Vice President, General Counsel
                                   and Secretary

                            XM EQUIPMENT LEASING LLC

                            By:    /s/ Joseph M. Titlebaum
                                ------------------------------------
                                   Joseph M. Titlebaum
                                   Executive Vice President, General Counsel
                                   and Secretary

AMENDMENT NO. 1 TO SECURITY AGREEMENT

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                           (CONTINUED SIGNATURE PAGE)

                            THE BANK OF NEW YORK,
                            as Collateral Agent

                            By:    /s/ John Guiliano
                                ------------------------------------
                                   Name: John Guiliano
                                   Title: Vice President

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