First American satellite
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In 1958, the United States entered the space age by launching the first successful orbiting satellite, Explorer-I, four months after the Soviet launch of Sputnik on 4 Oct 1957. Explorer-I measured cosmic radiation, and led to the discovery of the Van Allen radiation belt. Its instrumentation included temperature sensors, a micrometeorite impact microphone, and a ring of micrometeorite erosion guages. Data from these instruments were returned by a 60-mW transmitter operating on 108.03 MHz and a 10-milliwatt transmitter operating on 108.00 MHz. Explorer-I was 80-inch long, 6-in diam, weighed 31-lb with 18-lb of payload and was delivered into orbit using a Jupiter-C rocket. The orbit had a period of 114.9 minutes.
