自从1957年10月4日苏联成功发射了第一颗人造地球卫星以来,世界许多国家相继发射了各种用途的卫星。这些卫星广泛应用于科学研究,宇宙观测,气象观测,国际通信等许多领域。1958年12月美国宇航局(NASA)发射了“斯科尔”(SCORE)广播试验卫星,进行磁带录音信号的传输。1960年8月,又发射了“回声”(ECHO)无源发射卫星,首次完成了有源延迟中继 Since the Soviet Union successfully launched its first man-made earth satellite on October 4, 1957, many countries in the world have successively launched satellites for various purposes. These satellites are widely used in many fields such as scientific research, cosmic observation, meteorological observation, international communication and so on. In December 1958, NASA launched the SCORE radio test satellite to carry tape recorded signals. In August 1960, another “Echo” (ECHO) passive launch satellite was launched, completing the active delay relay for the first time