Being in space in itself can be terrifying, but add in the fact that it’s your first time up there, you’re alone, and you hear a mysterious knocking noise, and you have the recipe for a horror story.
That’s what happened to Yang Liwei, China’s first man in space, on his maiden flight – but no one has been able to confirm the cause of the sound.
In a recent interview, he has now recalled hearing ‘someone knocking the body of the spaceship just as knocking an iron bucket with a wooden hammer’, adding: “It neither came from outside nor inside the spaceship.”
Naturally, the strange noise left him feeling nervous, so and he looked out the porthole but couldn’t see anything out of the ordinary, the BBC reports.
The 2003 trip saw Yang become the first person sent into space by the Chinese space programme, orbiting earth several times during a 21-hour flight.
Since then, he has not been able to figure out what it was, neither up in space nor after returning to earth. He’s even tried – but failed – to recreate the sound so that experts could help him identify it.
He recalled the experience in a recent interview, telling Chinese media the mysterious knocking sounds occurred without any known reason.
According to the same media outlet, the sound has also been heard by subsequent Chinese astronauts on 2005 and 2008 missions.
But what actually caused it? Given that there is no medium for sound to travel, space would be expected to be silent.
Prof Goh Cher Hiang, an expert in space engineering at the National University of Singapore, told the BBC: “If it is knocking, there could be something physical ‘hitting’ the spacecraft carrying the astronaut,” but he stresses that any such suggestion is purely speculative.
His colleague Wee-Seng Soh offers a different explanation, suggesting it could have been ‘a result of expansion or contraction of the spaceship, especially since the temperature of the spaceship’s exterior could change considerably within the orbit’.
Whatever it is, after two other astronauts heard it, Yang Liwei now puts it down as a ‘normal phenomenon’.