It is the ultimate in Cold War legends: that at the dawn of the Space Age, in the late 1950s and throughout the 1960s, the Soviet Union had two space programmes, one a public programme, the other a ‘black’ one, in which far more daring and sometimes downright suicidal missions were attempted. It was assumed that Russia’s Black Ops, if they existed at all, would remain secret forever.

There are those who believe that somewhere in the vast blackness of space, about nine billion miles from the Sun, the first human is about to cross the boundary of our Solar System into interstellar space. His body, perfectly preserved, is frozen at –270 degrees C (–454ºF); his tiny capsule has been silently sailing away from the Earth at 18,000 mph (29,000km/h) for the last 45 years. He is the original lost cosmonaut, whose rocket went up and, instead of coming back down, just kept on going.

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Then, on 28 November 1960, the Bochum space observatory in West Germany said it had intercepted radio signals which it thought might have been a satellite. No official announcement had been made of any launch. “Our reaction was to immediately switch on the receivers and listen,” said Achille. After almost an hour of tuning in to static, the boys were about to give up when suddenly a tapping sound emerged from the hiss and crackle.

“It was a signal we recognised immediately as Morse code – SOS,” said Gian. But something about this signal was strange. It was moving slowly, as if the craft was not orbiting but was at a single point and slowly moving away from the Earth. The SOS faded into distant space. At 10.55pm on 2 February 1961, the brothers were scanning Russian frequencies as usual when Achille picked up a transmission from an orbiting capsule. They recorded the wheezing, struggling breathing of what they thought was a suffocating cosmonaut. The brothers contacted Professor Achille Dogliotti, Italy’s leading cardiologist and recorded his judgement. “I could quite clearly distinguish the clear sounds of forced, panting human breath,” said Dogliotti.

Two days later, the Soviet press agency announced that Russia had sent a seven-and-a-half-tonne spaceship the size of a single-decker bus into space on 2 February, which had burned up during re-entry. No further information was forthcoming.

Had the brothers captured the dying breaths of a cosmonaut?