Proponents of the Lost Cosmonauts theory concede that Yuri Gagarin was the first man to survive space travel, but claim that the Soviet Union attempted to launch two or more manned space flights prior to Gagarin's, and that at least two cosmonauts died in the attempts. Another cosmonaut, Vladimir Ilyushin, is believed to have landed off-course and been held by the Chinese government. The Government of the Soviet Union supposedly suppressed this information, to prevent bad publicity during the height of the Cold War.
The evidence cited to support Lost Cosmonaut theories is generally not regarded as conclusive, and several cases have been confirmed as hoaxes. In the 1980s, American journalist James Oberg researched space-related disasters in the Soviet Union, but found no evidence of these Lost Cosmonauts. Since the collapse of the Soviet Union in the early 1990s, much previously restricted information is now available. Even with the availability of published Soviet archival material and memoirs of Russian space pioneers, no hard evidence has emerged to support the Lost Cosmonaut stories.
Allegations
Purported Czech information leak
In December 1959, an alleged high-ranking Czech Communist leaked information about many purported unofficial space shots. Aleksei Ledovsky was mentioned as being launched inside a converted R-5A rocket, two more names of alleged cosmonauts claimed to have perished under similar circumstances were Andrei Mitkov, Sergei Shiborin and Marya Gromova.[2] Also in 1959, pioneering space theoretician Hermann Oberth claimed that a pilot had been killed on a sub-orbital ballistic flight from Kapustin Yar in early 1958. He provided no source for the story. In December 1959, the Italian news agency Continentale repeated the claims that a series of cosmonaut deaths on suborbital flights had been revealed by a high-ranking Czech communist. No other evidence of Soviet sub-orbital manned flights ever came to light.
Heinlein
In 1960, Robert A. Heinlein wrote in his article Pravda means 'Truth' (reprinted in Expanded Universe) that on May 15, 1960, while traveling in Vilnius, in the Soviet Union, he was told by Red Army cadets that the Soviet Union had launched a man into orbit that day, but that later the same day it was denied by officials. Apparently, no issues of Pravda could be found in Vilnius or, reportedly, other Soviet cities for that date. Heinlein wrote that there was an orbital launch, later said to be unmanned, on that day, but that the retro-rockets had fired at the wrong altitude, making recovery efforts unsuccessful.
According to Gagarin's biography these rumours were likely started as a result of two Vostok missions, equipped with dummies (Ivan Ivanovich) and human voice tape recordings, to check if the radio worked, that were made just prior to Gagarin's flight.
In a U.S. press conference on February 23, 1962, Col. Barney Oldfield revealed that a space cabin had indeed been orbiting the earth since 1960, as it had become jammed into its booster rocket. According to the NASA NSSDC Master Catalog, Korabl Sputnik 1, designated at the time 1KP or Vostok 1P, did launch on May 15, 1960 (one year before Gagarin).[6] It was a prototype of the later Zenit and Vostok manned launchers. The onboard TDU had ordered the retrorockets to fire, but due to a malfunction, the firing put the craft into a higher orbit. The re-entry capsule lacked a heatshield as there were no plans to recover it. Engineers had planned to use the vessel's telemetry data to determine if the guidance system had functioned correctly, so recovery was unnecessary
Lost Cosmonaut Conspiracy