Osoaviakhim-1

Osoaviakhim-1 was a record-setting, hydrogen-filled Soviet high-altitude balloon designed to seat a crew of three and perform scientific studies of the Earth's stratosphere. On January 30, 1934, on its maiden flight, which lasted over 7 hours, the balloon reached an altitude of 22,000 metres (72,000 ft). During the descent the balloon lost its buoyancy and plunged into an uncontrolled fall, disintegrating in the lower atmosphere. The three crew members, probably incapacitated by high g-forces in a rapidly rotating gondola, failed to bail out and were killed by the high-speed ground impact.According to public investigation reports, the crash was ultimately caused by a prolonged stay at record altitudes exceeding maximum design limits. The balloon, overheated by sunlight, lost too much lifting gas in the upper atmosphere. As it descended past the 12,000 metres (39,000 ft) mark, cooling down to ambient air temperature, a rapid loss of buoyancy caused a downward acceleration that triggered the structural failure of the suspension cables. The aircraft design was marked by numerous engineering flaws, notably insufficient ballast and faulty gondola suspension design, which all contributed to the loss of life.Later Soviet manned high-altitude balloons improved on safety devices and did not venture above 16,000 metres (52,000 ft); the program was nevertheless marked with accidents and failures and was terminated after the Osoaviakhim-2 launch failure in June 1940.