right|200px|thumb USSR-1 () was a record-setting, hydrogen-filled Soviet Air Forces high-altitude balloon designed to seat a crew of three and perform scientific studies of the Earth's stratosphere. On September 30, 1933, USSR-1 under Georgy Prokofiev's command set an unofficial world altitude record of .
right|200px|thumb USSR-1 () was a record-setting, hydrogen-filled Soviet Air Forces high-altitude balloon designed to seat a crew of three and perform scientific studies of the Earth's stratosphere. On September 30, 1933, USSR-1 under Georgy Prokofiev's command set an unofficial world altitude record of .
After the crash of Osoaviakhim-1 in January 1934 USSR-1 was retrofitted with a gondola parachute and a new gas envelope. June 26, 1935 it flew again as USSR-1 Bis. The balloon reached 16,000 meters where an accidental release of hydrogen, probably caused by a faulty valve, forced it into an unexpected descent. After expending all available ballast, two crew members bailed out on personal parachutes at low altitudes; the flight commander stayed on board and managed to perform a soft landing.
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