John Gridunov

John Ivanovich Gridunov (; 6 October 1926 – 12 August 2015) was a Russian engineer in the Soviet space program, working as to validate tests for the former Soviet spacecraft equipment. Being the so-called ground cosmonaut, Gridunov conducted several environmental tests, including the explosive decompression while testing a space suit. He is the only person to experience a short-time acceleration of 50 g (490 m/s2), during an emergency landing imitation.

Gridunov also sustained a 19 g (190 m/s2) centrifuge acceleration in the spine-chest direction without related accommodation. In the birth certificate Gridunov was recorded as John (Reed), in brackets. He died in August 2015 at the age of 88.