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A Soviet-era spacecraft meant to land on Venus in the 1970s is expected to plunge uncontrolled back to Earth, possibly within the first two weeks of May.

It’s too early to know where the half-tonne mass of metal might come down or how much of it will survive re-entry, according to space debris tracking experts.

Dutch scientist Marco Langbroek predicts the failed spacecraft will re-enter around 10 May. He estimates it will come crashing at around 242 kph, assuming it remains intact.

“While not without risk, we should not be too worried,” Langbroek said.

The object is relatively small and, even if it doesn’t break apart, “the risk is similar to that of a random meteorite fall, several of which happen each year. You run a bigger risk of getting hit by lightning in your lifetime,” he said.

The chance of the spacecraft actually hitting someone or something is small, he added, but “it cannot be completely excluded.”

What were the Soviet missions to Venus?

The Soviet Union launched the spacecraft known as Kosmos 482 in 1972, one of a series of Venus missions.

But it never made it out of Earth orbit because of a rocket malfunction.

Most of it came tumbling back to Earth within a decade. But Langbroek and others believe the landing capsule itself — a spherical object about one metre in diameter — has been circling the world in a highly elliptical orbit for the past 53 years, gradually dropping in altitude.

It’s possible that the nearly 500-kilogram spacecraft will survive re-entry.

It was built to withstand a descent through the carbon dioxide-thick atmosphere of Venus, said Langbroek of Delft University of Technology in the Netherlands.

Experts doubt the parachute system would work after so many years. The heat shield may also be compromised after so long in orbit.

Jonathan McDowell from the Harvard-Smithsonian Centre for Astrophysics said it would be better if the heat shield failed, which would cause the spacecraft to burn up during its dive through the atmosphere.

But if the shield holds, “it’ll re-enter intact and you have a half-tonne metal object falling from the sky.”

The spacecraft could re-enter anywhere between 51.7 degrees north and south latitude, or as far north as London and Edmonton in Canada’s Alberta, almost all the way down to South America’s Cape Horn.

But since most of the planet is water, “chances are good it will indeed end up in some ocean,” Langbroek said.