At the tail end of last month, China, in its quest for dominion over space exploration, successfully launched a 22-metric-ton module into orbit set to become a key part of its Tianhe space station. A Long March 5B heavy-lift rocket lifted off from the Wenchang spaceport carrying the module and after 492 seconds of flight, separated from it.
But while the module’s launch into orbit was a success, the fate of the mission launcher is less certain. The Long March 5B uses a core stage and four side boosters to carry its payload into space.
Yet, according to the latest reports, this core stage, having also reached orbit, is now likely to make an ‘uncontrolled reentry within the next few days as the atmosphere drags it back down to Earth. If indeed this happens, it will represent one of the largest incidents of uncontrolled reentry of a spacecraft, with the potential of causing serious damage if it landed in an inhabited area.
What makes its reentry all the more concerning is that scientists don’t really have any way to predict where it will land. Looking at the launcher’s current orbit, possible landing points could, reportedly, lie across a wide range of latitudes “a little farther north than New York, Madrid and Beijing and as far south as southern Chile and Wellington, New Zealand.”
US military radars on the ground have identified an object in space they believe to be the Long March 5B rocket body but the 30-meter-long, five-meter-wide core stage is in a 170 by 372-km altitude orbit and travelling at over seven kilometres per second.
As its orbit decays, it will become clearer where exactly the core stage will crash but calculating the atmospheric drag on it is challenging. This depends on a whole host of unknown variables including the density of the object, its speed and even minor atmospheric fluctuations.
But what scientists can say definitively is that its speed means that it is roughly orbiting the Earth once every 90 minutes so a change in reentry of just a handful of minutes will be enough to alter its reentry point by thousands of kilometres. Although the chances of it falling into the ocean -given that 70 per cent of the Earth’s surface is covered in water – are high, the risk of it landing in a populated area still exists.
There is already plenty of precedent for this. For instance, in 1979, SkyLab, a 77-tonne US space station burnt up over Western Australia littering the coastal town of Esperance with debris. The incident, as any similar incident since then, did not cause any deaths or serious injuries but that doesn’t necessarily mean that there is no threat at all. Just a year before SkyLab’s demise, Cosmos 954, a Soviet remote sensing satellite crashed into an uninhabited region in Northwest Canada peppering several hundreds of square kilometres with radioactive debris.
