Nikolayev followed Yuri Gagarin and German Titov into space, flying aboard Vostok 3 in 1962. In 1970, he and Vitali Sevastyanov flew aboard Soyuz 9 in an experiment in prolonged weightlessness, setting a nearly 18-day endurance record for life in space.

On their return to earth, the cosmonauts were found to have weakened considerably -- a phenomenon known as the Nikolayev effect -- and the experience demonstrated the need to set up suitable exercise regimes in later space stations.

Nikolayev married Valentina Tereshkova, the first woman in space, in 1963 and later became director of the Soviet cosmonaut training center and then a deputy in the Supreme Soviet until 1993.

SPACE.WIRE