The Soviet Union launched Sputnik 1 on 4 October 1957, placing the first artificial satellite in Earth orbit. Its radio signals made an orbital spacecraft a publicly observable reality. Although no person was aboard, it belongs at the start of this human-exploration timeline because it demonstrated a capability on which later crewed missions depended. Its political impact also accelerated the international competition that shaped the early Space Age.
Source: 1957: Sputnik 1 reaches orbit.
Image credit: Rept0n1x · CC BY-SA 3.0. Resized and JPEG compressed.
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