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2. Clarke, A.C., “Extraterrestrial Relays, Can Rocket Stations Give Worldwide Coverage?”, Wireless World, Vol. 51, Oct 1945, pp. 305-308.
3. Pierce, John R. (December 1990 (article)). “ECHO – America’s First Communications Satellite”. Reprinted from SMEC Vintage Electrics Volume 2 No. 1. Southwest Museum of Engineering, Communications and Computation.
4. NTIA Web site: www.ntia.doc.gov
5. Morgan, M. and Gordon, G. “Communications Satellite Handbook”, Wiley 1989