Sirius Satellite Radio (previously known as CD Radio) is a satellite constellation to provide digital radio to mobile receivers in North America.

Space Systems/Loral (SS/L) is designing and building four satellites called Sirius FM1 to FM4 for CD Radio Inc., which is developing a new satellite-to-car, CD-quality, radio broadcast system for the continental United States. The contract called for SS/L to deliver the high-powered, digital audio radio service (DARS) satellites for launch in 2000.

Motorists in cars and trucks equipped with CD Radio's revolutionary new antenna – the size of a silver dollar – will be able to receive broadcasts anywhere in the continental U.S. virtually without distortion. Signals will be transmitted via a new radio band, the S-band (2320-2332.5 MHz). The DARS satellites will be a new generation of SS/L's space-proven SSL-1300 bus.

The Sirius Satellite Radio is the first constellation, which operates in an elliptical 24 h orbit ranging from a perigee of 23975 km to an apogee of 46983 km, inclined at 63.4 degrees (Tundra orbit) to provide higher angles of elevation in the northern areas of north America.