PURCHASE MONEY LOAN GUARANTEE AND COLLATERAL AGREEMENT

Exhibit 10.28

EXECUTION VERSION

PURCHASE MONEY LOAN GUARANTEE AND COLLATERAL AGREEMENT

dated as of

February 17, 2009,

among

SIRIUS XM RADIO INC.,

ITS SUBSIDIARIES IDENTIFIED HEREIN

and

LIBERTY MEDIA CORPORATION,

as Collateral Agent

TABLE OF CONTENTS

Schedules

Exhibits

PURCHASE MONEY LOAN GUARANTEE AND COLLATERAL AGREEMENT dated as of February 17, 2009, among SIRIUS XM RADIO INC., a Delaware corporation (the “ Borrower ”), the subsidiaries of the Borrower from time to time party hereto and LIBERTY MEDIA CORPORATION (“ Liberty ”), as Collateral Agent.

Reference is made to the Term Credit Agreement dated as of February 17, 2009 (as amended, supplemented or otherwise modified from time to time, the “ Credit Agreement ”), among the Borrower, the Lenders from time to time party thereto and Liberty, as Administrative Agent and Collateral Agent. The Purchase Money Lenders have agreed to extend credit to the Borrower subject to the terms and conditions set forth in the Credit Agreement. The obligations of the Purchase Money Lenders to extend such credit are conditioned upon, among other things, the execution and delivery of this Agreement. The Subsidiary Guarantors are Affiliates of the Borrower, will derive substantial benefits from the extension of credit to the Borrower pursuant to the Credit Agreement and are willing to execute and deliver this Agreement in order to induce the Purchase Money Lenders to extend such credit. Accordingly, the parties hereto agree as follows:

ARTICLE I

Definitions

SECTION 1.01. Credit Agreement. (a) Capitalized terms used in this Agreement (including the preamble hereto) and not otherwise defined herein have the meanings specified in the Credit Agreement. All terms used in this Agreement and not defined herein or in the Credit Agreement have the meanings specified in Article 9 of the New York UCC (as defined herein).

(b) The rules of construction specified in Section 1.02 of the Credit Agreement also apply to this Agreement.

SECTION 1.02. Other Defined Terms. As used in this Agreement, the following terms have the meanings specified below:

“ Article 9 Collateral ” has the meaning assigned to such term in Section 3.01.

“ Borrower ” has the meaning assigned to such term in the preliminary statement of this Agreement.

“ Claiming Party ” has the meaning assigned to such term in Section 5.02.

“ Contributing Party ” has the meaning assigned to such term in Section 5.02.

“ Credit Agreement ” has the meaning assigned to such term in the preliminary statement of this Agreement.

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“ Intellectual Property ” means all intellectual property of every kind and nature now owned or hereafter acquired by any Loan Party, including inventions, designs, patents, copyrights, licenses, trademarks, trade secrets, confidential or proprietary technical and business information, know-how, show-how or other data or information, software and databases and all embodiments or fixations thereof and related documentation, registrations and franchises, and all additions, improvements and accessions to, and books and records describing or used in connection with, any of the foregoing.

“ Liberty ” has the meaning assigned to such term in the preliminary statement of this Agreement.

“ Loan Parties ” means the Borrower and the Subsidiary Guarantors.

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

“ Purchase Money Obligations ” means (a) the due and punctual payment by the Borrower of (i) the principal of and premium, if any, and interest (including interest accruing during the pendency of any bankruptcy, insolvency, receivership or other similar proceeding, regardless of whether allowed or allowable in such proceeding) on the Purchase Money Loans, when and as due, whether at maturity, by acceleration, upon one or more dates set for prepayment or otherwise, and (ii) all other monetary obligations of the Borrower to any of the Purchase Money Lenders under the Credit Agreement or any other Loan Document, including obligations to pay fees, expenses and indemnities, whether primary, secondary, direct, contingent, fixed or otherwise (including monetary obligations incurred during the pendency of any bankruptcy, insolvency, receivership or other similar proceeding, regardless of whether allowed or allowable in such proceeding), and (b) the due and punctual payment or performance of all other obligations of any Loan Party to any Purchase Money Lender under or pursuant to the Credit Agreement or any other Loan Document.

“ Purchase Money Secured Parties ” means (a) the Purchase Money Lenders, (b) the Administrative Agent, (c) the Collateral Agent, (d) the beneficiaries of each indemnification obligation undertaken by any Loan Party under any Loan Document in respect of the Purchase Money Loans, (e) each other Person to whom any of the Purchase Money Obligations is owed and (f) the permitted successors and assigns of each of the foregoing.

“ Satellite Codes ” has the meaning assigned to such term in Section 3.03(f).

“ Satellite Vendor ” means, with respect to any satellite, the prime contractor and manufacturer of such satellite.

“ Security Interest ” has the meaning assigned to such term in Section 3.01.

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“ Subsidiary Guarantors ” means (a) the Subsidiaries identified on Schedule I and (b) each other Subsidiary that becomes a party to this Agreement as a Subsidiary Guarantor after the Effective Date.

“ Term Loan Obligations ” means all Obligations other than the Purchase Money Obligations.

ARTICLE II

Guarantee

SECTION 2.01. Guarantee. (a) Each Subsidiary Guarantor unconditionally guarantees, jointly with the other Subsidiary Guarantors and severally, as a primary obligor and not merely as a surety, the due and punctual payment of the Purchase Money Obligations. Each Subsidiary Guarantor further agrees that the Purchase Money Obligations may be extended, increased or renewed, in whole or in part, or amended or modified without notice to or further assent from it, and that it will remain bound upon its guarantee notwithstanding any extension, increase or renewal, or amendment or modification, of any Purchase Money Obligation, and agrees to pay any and all expenses (including, without limitation, fees and expenses of counsel) incurred by any Agent or any Purchase Money Lender in enforcing any rights under this guarantee or any other Loan Document. Each Subsidiary Guarantor does hereby (i) waive notice of acceptance of this guarantee; (ii) waive any notices or demands that are not required by this Agreement or the Credit Agreement, as well as any other notices or demands that may otherwise be imposed by law; (iii) waive any and all rights that such Subsidiary Guarantor may have under any antideficiency statute or similar protections; (iv) agree not to assert any defense, right of set off or other claim which such Subsidiary Guarantor may have against the Borrower; (v) waive presentment, demand for performance, notice of nonperformance or dishonor, protest and notice of protest, promptness, diligence in collection and any and all formalities which otherwise might be legally required to charge such Subsidiary Guarantor with liability; and (vi) waive and agree not to assert or take advantage of assertion or claim that the automatic stay provided by 11 U.S.Code §362 (arising upon the voluntary or involuntary bankruptcy proceeding of the Borrower) or any other stay or delay provided under any debtor relief law (whether statutory, common law, case law or otherwise) of any jurisdiction whatsoever, now or hereafter in effect, which may be or become applicable to the Borrower, shall operate or be interpreted to stay, interdict, condition, reduce or inhibit the ability of the Collateral Agent to enforce any of its rights which the Collateral Agent may have against such Subsidiary Guarantor pursuant to this Agreement.

(b) Without limiting the generality of the foregoing, each Subsidiary Guarantor’s liability shall be extended to all amounts that constitute part of the Purchase Money Obligations and would be owed by any other Loan Party to any Agent or Purchase Money Lender under or in respect of the Loan Documents but for the fact that they are unenforceable or not allowable due to the existence of a bankruptcy, reorganization or similar proceeding involving such other Loan Party.

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(c) Each Subsidiary Guarantor, and by its acceptance of this guarantee, each Agent and each Purchase Money Lender, hereby confirms that it is the intention of all such Persons that this guarantee and the Purchase Money Obligations of each Subsidiary Guarantor hereunder not constitute a fraudulent transfer or conveyance for purposes of Title 11 U.S. Code, the Uniform Fraudulent Conveyance Act, the Uniform Fraudulent Transfer Act or any similar foreign, federal or state law to the extent applicable to this guarantee and the Purchase Money Obligations of each Subsidiary Guarantor hereunder. To effectuate the foregoing intention, the Collateral Agent, on behalf of the Purchase Money Lenders, and the Subsidiary Guarantors hereby irrevocably agree that the Purchase Money Obligations of each Subsidiary Guarantor under this guarantee at any time shall be limited to the maximum amount as will result in the Purchase Money Obligations of such Subsidiary Guarantor under this guarantee not constituting a fraudulent conveyance or transfer.

SECTION 2.02. Guarantee of Payment. Each Subsidiary Guarantor further agrees that its guarantee hereunder constitutes a guarantee of payment when due and not of collection, and waives any right to require that any resort be had by the Collateral Agent or any other Secured Party to any security held for the payment of the Purchase Money Obligations or to any balance of any deposit account or credit on the books of the Collateral Agent or any other Secured Party in favor of the Borrower or any other Person.

SECTION 2.03. No Limitations. (a) Except for termination of a Subsidiary Guarantor’s obligations hereunder as expressly provided in Section 6.13, the obligations of each Subsidiary Guarantor hereunder shall not be subject to any reduction, limitation, impairment or termination for any reason, including any claim of waiver, release, surrender, alteration or compromise of any of the Purchase Money Obligations, and shall not be subject to any defense or set-off, counterclaim, recoupment or termination whatsoever by reason of the invalidity, illegality or unenforceability of the Purchase Money Obligations or otherwise. Without limiting the generality of the foregoing, the obligations of each Subsidiary Guarantor hereunder shall not be discharged or impaired or otherwise affected by (i) the failure of the Collateral Agent or any other Purchase Money Secured Party to assert any claim or demand or to enforce any right or remedy under the provisions of any Loan Document or otherwise; (ii) any rescission, waiver, amendment or modification of, or any release from any of the terms or provisions of, any Loan Document or any other agreement, including with respect to any other Subsidiary Guarantor under this Agreement; (iii) the release of, or any impairment of or failure to perfect any Lien on or security interest in, any security held by the Collateral Agent or any other Purchase Money Secured Party for the Purchase Money Obligations or any of them; (iv) any default, failure or delay, willful or otherwise, in the performance of the Purchase Money Obligations; or (v) any other act or omission that may or might in any manner or to any extent vary the risk of any Subsidiary Guarantor or otherwise operate as a discharge of any Subsidiary Guarantor as a matter of law or equity (other than the indefeasible payment in full in cash of all the Purchase Money Obligations). Each Subsidiary Guarantor expressly authorizes the Secured Parties to take and hold security for the payment and performance of the Purchase Money Obligations, to exchange, waive or release any or all such security (with or without consideration), to

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enforce or apply such security and direct the order and manner of any sale thereof in their sole discretion or to release or substitute any one or more other Subsidiary Guarantors or obligors upon or in respect of the Purchase Money Obligations, all without affecting the obligations of any Subsidiary Guarantor hereunder.

(b) To the fullest extent permitted by applicable law, each Subsidiary Guarantor waives any defense based on or arising out of any defense of the Borrower or any other Subsidiary Guarantor or the unenforceability of the Purchase Money Obligations or any part thereof from any cause, or the cessation from any cause of the liability of the Borrower or any other Subsidiary Guarantor, other than the indefeasible payment in full in cash of all the Purchase Money Obligations. The Collateral Agent and the other Secured Parties may, at their election, foreclose on any security held by one or more of them by one or more judicial or nonjudicial sales, accept an assignment of any such security in lieu of foreclosure, compromise or adjust any part of the Purchase Money Obligations, make any other accommodation with the Borrower or any Subsidiary Guarantor or exercise any other right or remedy available to them against the Borrower or any Subsidiary Guarantor, without affecting or impairing in any way the liability of any Subsidiary Guarantor hereunder except to the extent the Purchase Money Obligations have been fully and indefeasibly paid in full in cash. To the fullest extent permitted by applicable law, each Subsidiary Guarantor waives any defense arising out of any such election even though such election operates, pursuant to applicable law, to impair or to extinguish any right of reimbursement or subrogation or other right or remedy of such Subsidiary Guarantor against the Borrower or any other Subsidiary Guarantor, as the case may be, or any security. Each Subsidiary Guarantor acknowledges that it will receive substantial direct benefits from the financing arrangements contemplated by the Loan Documents and that the waivers set forth in this Section 2.03 are knowingly made in contemplation of such benefits.

SECTION 2.04. Reinstatement. Each Subsidiary Guarantor agrees that its guarantee hereunder shall continue to be effective or be reinstated, as the case may be, if at any time payment, or any part thereof, of any Purchase Money Obligation is rescinded or must otherwise be restored by the Collateral Agent or any other Purchase Money Secured Party upon the bankruptcy or reorganization of the Borrower, any Subsidiary Guarantor or otherwise.

SECTION 2.05. Agreement to Pay; Subrogation. In furtherance of the foregoing and not in limitation of any other right that the Collateral Agent or any other Purchase Money Secured Party has at law or in equity against any Subsidiary Guarantor by virtue hereof, upon the failure of the Borrower or any Subsidiary Guarantor to pay any Purchase Money Obligation when and as the same shall become due, whether at maturity, by acceleration, after notice of prepayment or otherwise, each Subsidiary Guarantor hereby promises to and will forthwith pay, or cause to be paid, to the Collateral Agent for distribution to the applicable Purchase Money Secured Parties in cash the amount of such unpaid Purchase Money Obligation. Upon payment by any Subsidiary Guarantor of any sums to the Collateral Agent as provided above, all rights of such Subsidiary Guarantor against the Borrower or any other Subsidiary Guarantor arising as a result thereof by way of right of subrogation, contribution, reimbursement, indemnity or otherwise shall in all respects be subject to Article VI.

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SECTION 2.06. Information. Each Subsidiary Guarantor assumes all responsibility for being and keeping itself informed of the Borrower’s and each other Subsidiary Guarantor’s financial condition and assets, and of all other circumstances bearing upon the risk of nonpayment of the Purchase Money Obligations and the nature, scope and extent of the risks that such Subsidiary Guarantor assumes and incurs hereunder, and agrees that none of the Collateral Agent or the other Purchase Money Secured Parties will have any duty to advise such Subsidiary Guarantor of information known to it or any of them regarding such circumstances or risks.

ARTICLE III

Security Interests in Personal Property

SECTION 3.01. Security Interest. (a) As security for the payment in full of the Purchase Money Obligations, each Loan Party hereby pledges to the Collateral Agent, its permitted successors and assigns, for the benefit of the Purchase Money Secured Parties, and hereby grants to the Collateral Agent, its successors and assigns, for the benefit of the Purchase Money Secured Parties, a security interest (the “ Security Interest ”) in all right, title or interest in or to any and all of the assets and properties of such Loan Party described on Schedule II attached hereto and made a part hereof, as such Schedule II may be supplemented or modified from time to time to describe additional assets and properties of such Loan Party granted to secure such Loan Party’s Purchase Money Obligations (collectively, the “ Article 9 Collateral ”), together with all books and records pertaining to the Article 9 Collateral, and, to the extent not otherwise included, all Proceeds and products of the Article 9 Collateral and all assets and property affixed or appurtenant thereto.

(b) Each Loan Party hereby irrevocably authorizes the Collateral Agent at any time and from time to time to file in the proper jurisdictions any initial financing statements (including, if applicable, fixture filings) with respect to the Article 9 Collateral or any part thereof and amendments thereto and continuations thereof that contain the information required by Article 9 of the Uniform Commercial Code of each applicable jurisdiction for the filing of any financing statement or amendment, including (i) statements as to whether such Loan Party is an organization, the type of organization and any organizational identification number issued to such Loan Party and (ii) in the case of a financing statement filed as a fixture filing, a sufficient description of the real property to which such Article 9 Collateral relates. Each Loan Party agrees to provide such information to the Collateral Agent promptly upon request.

Each Loan Party also ratifies its authorization for the Collateral Agent to file in any proper jurisdiction any initial financing statements or amendments thereto if filed prior to the date hereof.

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(c) The Security Interest is granted as security only and shall not subject the Collateral Agent or any other Purchase Money Secured Party to, or in any way alter or modify, any obligation or liability of any Loan Party with respect to or arising out of the Article 9 Collateral (other than the duties expressly created hereunder).

SECTION 3.02. Representations and Warranties. The Loan Parties jointly and severally represent and warrant to the Collateral Agent and the other Purchase Money Secured Parties that:

(a) Each Loan Party has good and valid rights in and title to the Article 9 Collateral with respect to which it has purported to grant a Security Interest hereunder and has full power and authority to grant to the Collateral Agent, for the benefit of the Purchase Money Secured Parties, the Security Interest in such Article 9 Collateral pursuant hereto and to execute, deliver and perform its obligations in accordance with the terms of this Agreement, without the consent or approval of any other Person other than any consent or approval that has been obtained.

(b) The Perfection Certificate has been duly prepared, completed and executed and the information set forth therein, including the exact legal name and place of organization of each Loan Party, is correct and complete as of the Effective Date. The Uniform Commercial Code financing statements (including fixture filings, as applicable) or other appropriate filings, recordings or registrations prepared by the Collateral Agent based upon the information provided to the Collateral Agent in the Perfection Certificate for filing in each governmental, municipal or other office specified in Schedule 6 to the Perfection Certificate (or specified by notice from the Borrower to the Collateral Agent after the Effective Date in the case of filings, recordings or registrations required by Section 5.12 of the Credit Agreement), are all the filings, recordings and registrations that are necessary to publish notice of, perfect and protect the validity of and to establish a legal, valid and perfected security interest in favor of the Collateral Agent (for the benefit of the Purchase Money Secured Parties) in respect of all Article 9 Collateral in which the Security Interest may be perfected by filing, recording or registration in the United States (or any political subdivision thereof) and its territories and possessions, and no further or subsequent filing, refiling, recording, rerecording, registration or reregistration is necessary in any such jurisdiction, except as provided under applicable law with respect to the filing of continuation statements.

(c) The Article 9 Collateral is owned by the Loan Parties free and clear of any Lien, except for Liens created under the Loan Documents and the Permitted Liens. None of the Loan Parties has filed or consented to the filing of (i) any financing statement or analogous document under the Uniform Commercial Code or any other applicable laws covering any Article 9 Collateral or (ii) any assignment in which any Loan Party assigns any Article 9 Collateral or any security agreement or similar instrument covering any Article 9 Collateral with any foreign governmental, municipal or other office, which financing statement or analogous document, assignment, security agreement or similar instrument is still in effect, except, in each case, for Liens created under the Loan Documents and the Permitted Liens.

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SECTION 3.03. Covenants. (a) Upon the occurrence and during the continuance of an Event of Default, each Loan Party shall, upon reasonable request of the Collateral Agent, promptly prepare and deliver to the Collateral Agent a duly certified schedule or schedules in form and detail satisfactory to the Collateral Agent showing the identity, amount and location of any and all Article 9 Collateral.

(b) Each Loan Party agrees, at its own expense, to execute, acknowledge, deliver and cause to be duly filed all such further instruments and documents and take all such actions as the Collateral Agent may from time to time reasonably request to better assure, preserve, protect and perfect the Security Interest and the rights and remedies created hereby, including the payment of any fees and taxes required in connection with the execution and delivery of this Agreement, the granting of the Security Interest and the filing of any financing statements (including, if applicable, fixture filings) or other documents in connection herewith or therewith.

Without limiting the generality of the foregoing, each Loan Party hereby authorizes the Collateral Agent, with prompt notice thereof to the Loan Parties, to supplement this Agreement by supplementing Schedule II or adding additional schedules hereto to specifically identify any asset or item that may constitute Article 9 Collateral financed with the proceeds of any Purchase Money Loans; provided that any Loan Party shall have the right, exercisable within 10 days after it has been notified by the Collateral Agent of the specific identification of such additional Article 9 Collateral, to advise the Collateral Agent in writing of any inaccuracy (i) with respect to such supplement or additional schedule or (ii) of the representations and warranties made by such Loan Party hereunder with respect to such Collateral. Each Loan Party agrees that it will use its reasonable best efforts to take such action as shall be necessary in order that all representations and warranties hereunder shall be true and correct with respect to such Collateral within 30 days after the date it has been notified by the Collateral Agent of the specific identification of such Collateral.

(c) At its option, the Collateral Agent may, upon the occurrence and during the continuance of an Event of Default, discharge past due taxes, assessments, charges, fees and Liens at any time levied or placed on the Article 9 Collateral and not permitted pursuant to Section 5.07 or 6.08 of the Credit Agreement, and may pay for the mai