Showers with a chance of Chinese space debris

No, you are almost certainly not going to be hit by a 10-storey, 21 tonne piece of a rocket hurtling back to Earth.

That said, the chances are not zero. Part of China’s largest rocket, the Long March 5B, is tumbling out of control in orbit after launching a section of the country’s new space station last week. The rocket is expected to fall to Earth in what is called “an uncontrolled re-entry” sometime on Sunday.

Whether it splashes harmlessly in the ocean or impacts land where people live, why China’s space programme let this happen — again — remains unclear. And given China’s planned schedule of launches, more such uncontrolled rocket re-entries in the years to come are possible.

The country’s space programme has executed a series of major achievements in the past six months, including returning rocks from the moon and putting a spacecraft in orbit around Mars. Yet it continues to create danger, however small, for people all over the planet by failing to control the paths of rockets it launches.

“I think it’s negligent of them,” said Jonathan Mcdowell, an astrophysicist at the Centre for Astrophysics in Cambridge, Massachusetts, who tracks the comings and goings of objects in space. “I think it’s irresponsible.”

The piece that will be dropping out of the sky is the core booster stage of the Long March 5B, which was designed to lift the big, heavy pieces of the space station. For most rockets, the lower stages usually drop back to Earth immediately after launch. Upper stages that reach orbit usually fire the engine again after releasing their payloads, guiding them toward reentry in an unoccupied area like the middle of an ocean.

Over the past three decades, only China has lifted rocket stages this big to orbit and left them to fall somewhere at random, Mcdowell said.

“The orbital inclination of 41.5 degrees means the rocket body passes a little farther north than New York, Madrid and Beijing and as far south as southern Chile,” Spacenews reports. That puts Australia and the North Island at the southern end of the potential debris shower.

Friday, the Aerospace Corp, a nonprofit largely financed by the federal government that performs research and analysis, predicts reentry will occur Saturday at 11.43pm EST (3.43pm Sunday NZST). If that is accurate, debris could shower down over northeastern Africa, over Sudan.

However, uncertainty over the time — give or take 16 hours — and location remain large. A day before, Aerospace’s prediction put re-entry more than one hour earlier, over the eastern Indian Ocean.

When the booster burns up depends, for instance, on the sun. A rise in the intensity of the solar wind — charged particles spewed out by the sun — would puff out Earth’s atmosphere, increasing atmospheric drag on the rocket booster and speeding its fall. The tumbling of the rocket stage also complicates calculations.

The US Space Command and Russia’s space agency are both tracking the rocket core. A Russian statement noted that the re-entry would not “affect the territory of the Russian Federation”.

The Space Command promised regular updates ahead of a potential re-entry.

Because the booster is travelling at 27,880km/h, a change of minutes shifts the debris by hundreds or thousands of miles. It is only a few hours before re-entry that the predictions become more precise.