Unmanned space vehicles can have many different sizes and dimensions. Mostly, they carry technical equipment that transmits data back to the earth by radio. The first artificial space vehicle was Sputnik I.
It was launched on October 4th, 1957 in the erstwhile Soviet Union and orbited the earth in 96.2 minutes. The satellite was made of aluminium and carried equipment that transmitted data on meteorites, cosmic rays and temperatures of the upper atmosphere layers.
After 57 days, Sputnik I returned to the atmosphere and burned up. On November 3rd, 1957, Sputnik II carried a dog called Laika into space to get the first bio-medical measurements. While Sputnik II was still in orbit, on January 31st, 1958, Explorer I was launched by the United States from Cape Kennedy (today called Cape Canaveral).
It also collected data on cosmic radiation and meteorites. Some of these measurements led to the discovery of the Van-Allen radiation belt. In 1958, Vanguard 2 showed that the earth is not a perfect sphere, but is flattened at the poles. Even at that time, solar energy was used for a period of six years for transmitting data.
