CBS RADIO ENGINEERING CHIEF, TONY MASIELLO, JOINS XM RADIO AS VICE PRESIDENT BROADCAST OPERATIONS

National, September 16, 1999 -- CBS Radio Networks engineering executive, Anthony J. Masiello, joins XM Satellite Radio as Vice President of Broadcast Operations. Mr. Masiello, who has more than 28 years experience in radio engineering, will oversee the build out of XM's state-of-the-art multi-studio programming complex. The announcement was made today by Jack Wormington, Senior Vice President of Engineering and Operations, to whom Mr. Masiello will report.

"Tony brings massive experience in radio engineering to the unprecedented task of designing and implementing what promises to be the largest radio facility in the country," said Mr. Wormington. "During his 12-year tenure at CBS, Tony was responsible for, among many other things, bringing the radio networks' broadcast operations into the digital age. That experience will serve XM well." Mr. Masiello will be based in XM's Washington, DC, headquarters.

Most recently, Mr. Masiello served as Vice President, Technical Operations for CBS Radio Networks, where he had overall technical responsibility for the network; designed and implemented the conversion of its broadcast center facilities from analog to digital audio; and designed and implemented CBS's new central control. He developed and pioneered the use of audio compression with switched digital terrestrial systems, such as switched 56 and ISDN. In addition, he spearheaded the development and implementation of the PACE digital audio workstation system for use in radio news operations.

Mr. Masiello joined CBS Radio in 1988 as Director of Technical Operations where he held overall technical responsibility for all CBS Radio owned and operated radio stations. He began his broadcast engineering career in 1971 at ABC Radio Networks in New York City, as Operations Supervisor.

XM Satellite Radio, a wholly owned subsidiary of American Mobile Satellite Corporation (NASDAQ: SKYC), is developing a new band of radio. The system will use direct satellite-to-receiver broadcasting technology to provide listeners in their cars and at home with crystal-clear sound seamlessly from coast to coast. The subscription service is scheduled to start during the first half of 2001 for $9.95 a month.

Through its XM Originals programming unit, XM plans to offer an innovative mix of music, talk, news, sports and children's formats. To complement its original programming, XM has signed programming agreements with a number of premier content providers, including USA TODAY, the BBC World Service, Black Entertainment Television, the Hispanic Broadcasting Corporation (formerly Heftel), Bloomberg News Radio, C-SPAN Radio, CNN/Financial Network, CNN/Sports Illustrated, The Weather Channel and many others.

XM is partnering with industry leaders to build its service. General Motors was the first automobile manufacturer to announce that it would install satellite radio in its vehicles. And, XM is the service GM will distribute and market. Alpine, Delphi Delco, Pioneer and Sharp will design, manufacture and market AM/FM/XM radios; and Hughes and Alcatel are building XM's satellites, the most powerful commercial satellites ever ordered. XM's investors include industry leaders Clear Channel Communications Inc.; DIRECTV, Inc., a unit of Hughes Electronics Corporation; the General Motors Corporation; and a private investment group comprised of Columbia Capital, Telcom Ventures L.L.C., and Madison Dearborn Partners, which together recently invested $250 million in the company. XM Satellite Radio obtained one of two satellite digital audio radio service (SDARS) licenses from the Federal Communications Commission in October 1997. First there was AM, then FM and soon . . . XM Satellite Radio. For more information, please visit XM's new website: www.xmradio.com.

Factors that could cause forward-looking statements in this news release to differ materially from actual results are discussed in XM's Registration Statement on Form S-1 (No.333-38619) filed with the Securities and Exchange Commission on July 23, 1999, as the same may be amended, and other periodic filings the company will make with the Securities and Exchange Commission.