Moon landing anniversary: Key events in the history of space exploration

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As the 40th anniversary of the moon landing approaches, we look at key events in the history of space exploration.

4 October 1957: The Soviet Union launches Sputnik 1, the first Earth-orbiting artificial satellite, igniting the space race. Sputnik's radio signals continue for 22 days until the transmitter batteries run out. It burns up on 4 January 1958 as it re-enters the Earth's atmosphere