Exhibit 8.1

[Letterhead of Simpson Thacher & Bartlett LLP]

October 1, 2007

Sirius Satellite Radio Inc.
1221 Avenue of the Americas, 36^th Floor
New York, New York 10020

Re: Sirius/XM Merger

Ladies and Gentlemen:

     We have acted as counsel to Sirius Satellite Radio Inc., a Delaware corporation (“Sirius”), in connection with the Agreement and Plan of Merger, dated as of February 19, 2007, (including the exhibits thereto, the “Merger Agreement”), among Sirius, Vernon Merger Corporation, a Delaware corporation and a direct wholly-owned subsidiary of Sirius (“Merger Sub”), and XM Satellite Radio Holdings Inc., a Delaware corporation (“XM”), pursuant to which Merger Sub shall be merged with and into XM with XM surviving as a wholly-owned subsidiary of Sirius (the “Merger”) on the terms and conditions set forth therein. The time at which the Merger becomes effective is hereafter referred to as the “Effective Time.” For purposes of this opinion, capitalized terms used and not otherwise defined herein shall have the meaning ascribed thereto in the Merger Agreement. This opinion is being delivered in connection with the filing of the registration statement on Form S-4 (Registration No. 333-144845) (as amended, the “Registration Statement”) filed by Sirius with the Securities and Exchange Commission under the Securities Act of 1933, as amended, relating to the proposed Merger pursuant to the Merger Agreement and to which this opinion appears as an exhibit.

     We have examined (i) the Merger Agreement, (ii) the Registration Statement and (iii) the representation letters of Sirius, Merger Sub and XM delivered to us for purposes of this opinion (the “Representation Letters”). In addition, we have examined, and relied as to matters of fact upon, originals or copies, certified or otherwise identified to our satisfaction, of such corporate records, agreements, documents and other instruments and made such other inquiries as we have deemed necessary or appropriate to enable us to render the

opinion set forth below. In such examination, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies, and the authenticity of the originals of such latter documents. We have not, however, undertaken any independent investigation of any factual matter set forth in any of the foregoing.

     In rendering such opinion, we have assumed, with your permission, that (i) the Merger will be effected in accordance with the Merger Agreement, (ii) the facts, information, representations, covenants and agreements concerning the Merger set forth in the Merger Agreement and the Registration Statement are true, complete and correct and will remain true, complete and correct at all times up to and including the Effective Time, (iii) the representations made by Sirius, Merger Sub and XM in their respective Representation Letters are true, complete and correct and will remain true, complete and correct at all times up to and including the Effective Time and (iv) any representations made in the Merger Agreement or the Representation Letters “to the knowledge of”, or based on the belief of Sirius, Merger Sub and XM or similarly qualified are true, complete and correct and will remain true, complete and correct at all times up to and including the Effective Time, in each case without such qualification. We have also assumed that the parties have complied with and, if applicable, will continue to comply with, the covenants contained in the Merger Agreement.

     Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that under current law, the Merger will be treated for United States federal income tax purposes as a reorganization within the meaning of Section 368(a) of the Code.

     We express our opinion herein only as to those matters specifically set forth above and no opinion should be inferred as to the tax consequences of the Merger under any state, local or foreign law, or with respect to other areas of United States federal taxation. We do not express any opinion herein concerning any law other than the federal law of the United States.

     We hereby consent to the filing of this opinion as Exhibit 8.1 to the Registration Statement, and to the references to our firm name therein.