Vostok 5 launched 1963

Vostok 5 cosmonaut Valery Bykovsky

Vostok 5, launched June 14, 1963, carried one cosmonaut and holds the record for the longest solo space flight.  The Soviets intended Valery Bykovsky to stay in orbit for eight days but circumstances caused them to shorten his flight to five days.

The sun was experiencing increased solar flare activity and scientists were concerned that the spacecraft's orbit might decay sooner than eight days.

Bykovsky returned to Earth June 19.