On 12 April 1961, Yuri Gagarin flew aboard Vostok 1 and became the first human to orbit Earth. A single flight moved the question from whether a person could enter space to how people could survive, return and work there. It earns its place as the transition from robotic precursors to human presence. The achievement depended on a complete launch, life-support and return system, rather than a rocket alone.

Source: 1961: Yuri Gagarin’s orbital flight.

Image credit: Arto Jousi / /Suomen valokuvataiteen museo / Alma Media / Uuden Suomen kokoelma; Restored by Adam Cuerden · Public domain. Resized and JPEG compressed.