Early Earth Satellites

The first artificial satellite of the Earth was the Russian Sputnik; the year of launch, 1957, marked the beginning of the space age. The first U.S. satellite was the Explorer, which discovered the inner Van Allen radiation belt. The Vangaurd series of rockets in the late 50's also contributed. The Pioneer series started with 1-3 in 1958, giving new data about the Earth including the discovery of a second Van Allen belt.

Sputnik

Sputnik 1 was the first successful artificial earth satellite. It was launched by the Soviet Union in October 1957. It was an aluminum sphere of diameter 58 cm with a mass of 83 kg. It orbited the earth in 96.2 min in an elliptic orbit with apogee 946 km and perigee 227 km. It carried instruments which transmitted data about cosmic rays, meteoroids, temperature, and air density. It lasted 57 days before decay of the orbit brought it to a fiery reentry into the atmosphere.

Sputnik 2 was launched on November 3, 1957 with a dog aboard and relayed the first physiological data from space. Sputnik 2 remained aloft for 162 days. The U.S. launched its first satellite, Explorer 1, on January 31, 1958 while Sputnik 2 was still aloft.

Sputnik 3, launched on May 15, 1958, was a massive 1327 kg spacecraft which spent two years aloft measuring solar radiation, cosmic rays, and magnetic fields.

Explorer

Spurred on by the prior launch of the Soviet Union's Sputnik, the U.S. launched its first satellite, Explorer 1, on January 31, 1958. It was a cylindrical spacecraft of diameter 15 cm and length 203 cm with mass 14 kg. It transmitted measurements of cosmic rays for 112 days and gave the first satellite data on radiation.

That data led to the discovery of the Van Allen belts. It carried a Geiger counter for radiation detection.

After the launching of Vangaurd 2, Explorer 3 was launched on March 26, 1958.

Vangaurd

Vangaurd 2 was launched by the U.S. on March 17, 1958. It transmitted data which allowed precise measurement of the earth and showed that the earth is slightly pear-shaped. Vangaurd had an effective solar array to power it and was able to transmit signals for more than six years.