Exhibit 5.1

                                         [Opinion of Simpson Thacher & Bartlett]





                                                    January 28, 2003


Sirius Satellite Radio Inc.
1221 Avenue of the Americas
36th 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-4 (the "Registration Statement") filed by the Company with
the Securities and Exchange Commission (the "Commission") under the Securities
Act of 1933, as amended, relating to the issuance by the Company of 596,669,765
shares of common stock, par value $0.001 per share (the "Exchange Securities").
The Exchange Securities will be offered by the Company in exchange for the
various debt securities of the Company described in the Registration Statement.

                  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 records, agreements, instruments and
other documents and have made such other and further investigations as we have
deemed relevant and necessary in connection with the opinion expressed herein.
As to questions of fact material to this opinion, we have relied upon
certificates of public officials and of officers and representatives of the
Company.

                  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.

                  Based upon the foregoing, and subject to the qualifications
and limitations stated herein, we are of the opinion that (1) when the Board of
Directors of the Company (the "Board")






Sirius Satellite Radio Inc.            -2-                    January 28, 2003


has taken all necessary corporate action to authorize and approve the issuance
of the Exchange Securities, (2) when the requisite number of holders of the
Company's common stock has approved all matters necessary to the authorization
and issuance of the Exchange Securities and (3) upon issuance and delivery in
accordance with the terms of the exchange offer approved by the Board, the
Exchange Securities will be validly issued, fully paid and nonassessable.

                  We are members of the Bar of the State of New York and we do
not express any opinion herein concerning any law other than the Delaware
General Corporation Law.

                  We hereby consent to the filing of this opinion letter as
Exhibit 5.1 to the Registration Statement and to the use of our name under the
caption "Legal Matters" in the Prospectus and Solicitation Statement included in
the Registration Statement.


                                                  Very truly yours,

                                                  /s/ SIMPSON THACHER & BARTLETT

                                                  SIMPSON THACHER & BARTLETT