History's best-known science satellites have grown to enormous proportions

More than 58 years have passed since Sputnik 1 became the first artificial satellite to orbit Earth. Launched by the Soviet Union on October 4, 1957, Sputnik 1 consisted of a 23-inch-diameter metal sphere with four radio antennas — that's it.

Compared with the highly sophisticated satellites in orbit today, including the Hubble Space Telescope and the International Space Station, Sputnik 1 is not much to look at. But this satellite gave scientists critical information about Earth's upper atmosphere that informed later launches.

Since that October day in 1957, space agencies and private companies around the world have launched thousands of artificial satellites into orbit around Earth as well as toward more distant worlds like Jupiter, Saturn, and Pluto, and beyond. As technology continues to advance, so will the size and sophistication of our space-based instruments.

Here are some of history's best-known satellites and how they compare in size:

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