PROSPECTUS SUPPLEMENT
(to Prospectus dated August 13, 2004)

$300,000,000

2¹⁄2% Convertible Notes due 2009

      This prospectus supplement relates to resales of our 2¹⁄2% Convertible Notes due 2009 issued in private offerings and 68,027,220 shares of our common stock issuable upon conversion of the notes, plus an indeterminate number of additional shares of common stock that may be issued from time to time upon conversion of the notes as a result of antidilution adjustments, in circumstances described in the prospectus to which this prospectus supplement refers.

      This prospectus supplement to our prospectus dated August 13, 2004 contains additional information about the selling securityholders.

      You should read this prospectus supplement in conjunction with the prospectus. This prospectus supplement updates information in the prospectus and, accordingly, to the extent inconsistent, the information in this prospectus supplement supercedes the information contained in the prospectus.

      Investing in the securities offered in the prospectus involves risk. See “Risk Factors” beginning on page 4 of the prospectus.

      Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement. Any representation to the contrary is a criminal offense.

      The date of this Prospectus Supplement is October    , 2004

      As used in this prospectus supplement, the terms “Sirius,” “company,” “we,” “our,” “ours,” and “us” refer to Sirius Satellite Radio Inc., except where the context otherwise requires or as otherwise indicated. When we refer to “common stock” throughout this prospectus supplement, we include all rights attaching to our common stock under any stockholder rights plan then in effect.

      You should rely only on the information contained in this prospectus supplement and the prospectus to which it refers. We have not authorized any other person to provide you with different or additional information. If anyone provides you with different or additional information, you should not rely on it. We are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus supplement and the prospectus to which it refers is accurate only as of their respective dates.

WHERE YOU CAN FIND MORE INFORMATION

      We are subject to the information requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and we file annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission (the “SEC”). You may read and copy any document that we file at the SEC's public reference room facility located at 450 Fifth Street, N.W., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the public reference room. The SEC maintains an Internet site at http://www.sec.gov that contains reports, proxy and information statements and other information regarding issuers, including us, that file documents with the SEC electronically through the SEC's electronic data gathering, analysis and retrieval system known as EDGAR.

      Our common stock is listed on the Nasdaq National Market under the symbol “SIRI.” Our reports, proxy statements and other information may also be reviewed at the offices of the National Association of Securities Dealers, Inc., 1735 K Street, N.W., Washington, D.C. 20006.

      This prospectus supplement is part of a Registration Statement on Form S-3 that we filed with the SEC. This prospectus supplement incorporates by reference important business and financial information that we file with the SEC and that we are not including in or delivering with this prospectus supplement. Incorporated documents are considered part of this prospectus supplement, and we can disclose the important information to you by referring you to those documents.

      We incorporate by reference the documents listed below (excluding any information furnished pursuant to Item 9 or Item 12 on any Current Report on Form 8-K) to the extent they have been filed with the SEC:

      We also incorporate by reference all documents to the extent they have been filed with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act (excluding any information furnished pursuant to Item 9 or Item 12 on any Current Report on Form 8-K) after the date of this prospectus supplement and until such time as the selling securityholders have sold all the notes or common stock issuable upon conversion of the notes. Information in this prospectus supplement supersedes related information in the documents listed above, and information in subsequently filed documents supersedes related information in both this prospectus supplement and the incorporated documents.

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      We will promptly provide, without charge to you, upon written or oral request, a copy of any or all of the documents incorporated by reference in this prospectus supplement, other than exhibits to those documents, unless the exhibits are specifically incorporated by reference in those documents. Requests should be directed to:

Patrick L. Donnelly
Executive Vice President, General Counsel and Secretary
Sirius Satellite Radio Inc.
1221 Avenue of the Americas, 36th Floor
New York, New York 10020
(212) 584-5100

      The information appearing under the section entitled “Selling Securityholders” in the prospectus is amended and restated by the infomation appearing below.

SELLING SECURITYHOLDERS

      The notes were originally issued to Morgan Stanley & Co. Incorporated, as initial purchaser, in private offerings on February 20, 2004 and March 31, 2004. The initial purchaser has advised us that the notes were resold in transactions exempt from the registration requirements of the Securities Act to “qualified institutional buyers,” as defined by Rule 144A under the Securities Act. Selling securityholders, including their transferees, pledgees, donees or successors, may from time to time offer and sell pursuant to this prospectus supplement any or all of the notes and the common stock into which the notes are convertible.

      The table below sets forth information with respect to the selling securityholders, the principal amount of the notes and the number of shares of common stock into which the notes are convertible beneficially owned by each selling securityholder that may be offered pursuant to this prospectus supplement. None of the selling securityholders has had within the past three years any material relationship with us or any of our affiliates.

      We have prepared the table based on information given to us by, or on behalf of, the selling securityholders on or before October 21, 2004. Because the selling securityholders may offer, pursuant to this prospectus supplement, all or some portion of the notes or common stock listed below, no estimate can be given as to the amount of notes or common stock that will be held by the selling securityholders upon consummation of any sales. In addition, the selling securityholders listed in the table may have sold, transferred or otherwise disposed of, in transactions exempt from the registration requirements of the Securities Act, some or all of their notes since the date as of which the information in the table is presented.

      Information about the selling securityholders may change over time. Any changed information given to us by the selling securityholders will be set forth in prospectus supplements if and when necessary.

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PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

      The following table sets forth the various expenses payable by the registrant in connection with the issuance and distribution of the notes and underlying common stock being registered hereby, other than underwriting discounts and commissions. All the amounts shown are estimates, except the SEC registration fee. All of such expenses are being borne by the registrant.

Item 15. Indemnification of Directors and Officers.

      Section 145 of the DGCL permits each Delaware business corporation to indemnify its directors, officers, employees and agents against liability for each such person's acts taken in his or her capacity as a director, officer, employee or agent of the corporation if such actions were taken in good faith and in a manner which he or she reasonably believed to be in or not opposed to the best interests of the corporation, and with respect to any criminal action, if he or she had no reasonable cause to believe his or her conduct was unlawful. Article VII of our Amended and Restated By-Laws provides that we, to the full extent permitted by Section 145 of the DGCL, shall indemnify all of our past and present directors and may indemnify all of our past or present employees or other agents. To the extent that a director, officer, employee or agent of ours has been successful on the merits or otherwise in defense of any action, suit or proceeding referred to in such Article VII, or in defense of any claim, issue or matter therein, he or she shall be indemnified by us against actually and reasonably incurred expenses in connection therewith. Such expenses may be paid by us in advance of the final disposition of the action upon receipt of an undertaking to repay the advance if it is ultimately determined that such person is not entitled to indemnification.

      As permitted by Section 102(b)(7) of the DGCL, our Amended and Restated Certificate of Incorporation provides that no director shall be liable to us for monetary damages for breach of fiduciary duty as a director, except for liability:

      We have obtained a policy insuring us and our directors and officers against certain liabilities, including liabilities under the Securities Act.

Item 16. Exhibits

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* Filed previously.

Item 17. Undertakings.

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      Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment No. 1 to the registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, State of New York, on October 22, 2004.

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      Pursuant to the requirements of the Securities Act, this Post-Effective Amendment No. 1 to registration statement has been signed by the following persons in the capacities and on the dates indicated.

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EXHIBIT INDEX

* Previously filed.