Exhibit 5.1

Simpson Thacher & Bartlett LLP
425 Lexington Avenue
New York, New York 10017

January 10, 2006

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

Ladies and Gentlemen:

        We have acted as counsel to Sirius Satellite Radio Inc., a Delaware corporation (the “Company”), in connection with the Registration Statement on Form S-3 (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”), relating to an aggregate of 34,375,000 shares of common stock, par value $0.001 per share, that may be sold from time to time by certain selling stockholders of the Company (the “Shares”).

        We have examined the Registration Statement and a form of the share certificate, which has been filed with the Commission as an exhibit to the Registration Statement. We also have examined the originals, or duplicates or certified or conformed copies, of such corporate records, agreements, documents and other instruments and have made such other investigations as we have deemed relevant and necessary in connection with the opinions hereinafter set forth. As to questions of fact material to this opinion, we have relied upon certificates or comparable documents of public officials and of officers and representatives of the Company.

        In rendering the opinion set forth below, 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.

        Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that the Shares have been validly issued and are fully paid and nonassessable.