A Soviet probe launched more than half a century ago is due to return to Earth in the next week or two, and there’s every chance that the vehicle will make it all the way to our planet’s surface.
A Venera-8 descent module (click to enlarge) Source: NASA archive
“You wouldn’t want it bashing you on the head,” wrote astronomer Jonathan McDowell of the space junk set to re-enter Earth’s atmosphere. That is if, as seems likely, the object in question is indeed the entry capsule of a failed Soviet mission to Venus.
Specifically, that would make the object a key component of Kosmos 482, which launched in March 1972 from Baikonur on top of a Molniya rocket with the intention of getting to the harsh alien world. Just days earlier, a Soviet Venera-8 probe had blasted off, and its descent module ultimately made it to the surface of Venus and survived for 50 minutes. It’s understood Kosmos 482 included a Venera-8-like descent module.
The usual mission profile of the time was to launch a spacecraft into a parking orbit around the Earth before firing up an engine to send the vehicle on a trajectory to Venus. Unfortunately, Kosmos 482 never made it out of Earth orbit, most likely due to a premature shutdown of the engine. As such, rather than receiving a Venera designation, the stranded spacecraft was given the name Kosmos 482, and the Soviet space program moved on.
While the space race ebbed and flowed, Kosmos 482 continued orbiting. According to McDowell, US tracking found three objects in the 206 x 9,800 km orbit, where the ill-fated mission ended up.
“One,” he wrote, “was labelled as Kosmos-482, one as the rocket stage, and one as debris. ‘Kosmos-482’ and the ‘rocket stage’ (1972-023A and B) had relatively rapid orbital decay and reentered in 1981 and 1983 respectively.
“The debris object, 1972-023E, came down more slowly.”
In 2000, McDowell wondered if 23E (object 6073) might be the separated Venera descent sphere. It seemed likely – the object was about the right size. “In June 2002,” he said, “the NORAD satellite catalog starting labelling 6073 as the Venera descent sphere too.” He added: “Probably just a coincidence.”
The original mission called for the probe to descend to the surface of Venus by parachute following entry into the atmosphere. The parachute mechanism will be long dead by now, but the half-ton probe itself will be coming back to Earth regardless. It is also likely to survive re-entry thanks to a heat shield designed to withstand the atmosphere of Venus.
The good news is that the probe is inert – it has no nuclear material to worry about. The bad news is that it weighs almost 500 kg and could be travelling at around 240 km/h (150 mph) when it hits, according to Dutch lecturer on space situational awareness Dr Marco Langbroek. Exactly where the probe will come down is unclear; Langbroek wrote that current modelling puts it anywhere between latitude 52 N and 52 S. As the reentry nears, the estimates will become more refined.
It is possible the heat shield will have failed after spending so long in orbit and the probe will burn up harmlessly. But it is also possible that it remains intact, and the probe will hit the Earth’s surface. The chances of it striking a person are vanishingly small and in the order of one in several thousand. But not zero.
McDowell is correct – you wouldn’t want it bashing you on the head. ®