vailable to the public. XM Satellite Radio launched commercial service in limited areas of the continental United States on September 25, 2001. (They were originally going to launch service September 12, but postponed the event because of the terrorist attacks on the United States.) WorldSpace is already broadcasting in Africa and Asia, and will begin broadcasting in South America sometime soon. Satellite radio companies are comparing the significance of their service to the impact that cable TV had on television 30 years ago. Listeners won't be able to pick up local stations using satellite radio services, but they will have access to hundreds of stations offering a variety of music genres. Each company has a different plan for its broadcasting system, but the systems do share similarities. Here are the key components of the three satellite radio systems: •Satellites •Ground repeaters •Radio receivers Taking a closer look, you will see slight variances in the three satellite radio companies' systems. In the next three sections, we will profile each of the companies offering satellite radio services.XM Radio XM Radio uses two Boeing HS 702 satellites, appropriately dubbed "Rock" and "Roll," placed in parallel geostationary orbit, one at 85 degrees west longitude and the other at 115 degrees west longitude. Geostationary Earth orbit (GEO) is about 22,223 miles (35,764 km) above Earth, and is the type of orbit most commonly used for communications satellites. The first XM satellite, "Rock," was launched on March 18, 2001, with "Roll" following on May 8. XM Radio has a third HS-702 satellite on the ground ready to be launched in case one of the two orbiting satellites fails. http://www.washtech.com/specialreports/xmsr_explainer.htm) XM Radio's ground station transmits a signal to its two GEO satellites, which bounce the signals back down to radio receivers on the ground. The radio receivers are programmed to rece...
