For the second time in the space of a year, an enormous out-of-control Chinese space rocket is set to come back down to Earth - and where it might land is anybody's guess.
If the timing is right, it could even be New Zealand - the 21-tonne Long March 5B rocket is expected to pass over us several times in the next week, including Wellington and Auckland.
The rocket - also known as CZ-5B - launched on April 29, delivering the core module 'Tianhe' of the new Chinese space station 'Tiangong' to orbit.
But instead of dropping off early into a designated safe area, the rocket also entered orbit - and was last measured at about 320km high, dropping about 50km in five days.
At some point atmospheric drag will become too much, and it'll come careening back to Earth - just like a previous Long March rocket did in April 2020, pieces of it landing in the Atlantic Ocean and on a village in Cote d'Ivoire, western Africa. No one was hurt.
Travelling at more than 27,600km/h and orbiting the entire planet in just 90 minutes, it's hard to know exactly where the rocket will fall. The one that came down last year had just minutes earlier passed directly over New York City.
The current estimate for CZ-5B's reentry is 1pm on Monday, May 10, plus or minus 41 hours, according to aerospace.org. Space junk and satellite tracking site orbit.ing-now.com shows its orbit as crossing over New Zealand a few times on Tuesday, four more times on Thursday - flying over Wellington, Auckland and Northland - and again on Saturday, this time buzzing the central North Island, upper South Island and the lower North Island.
More passes will take place during aerospace.org's predicted 82-hour crash window. Wellington's considered particularly at risk, being at latitude 41.3S - the rocket's orbit spending plenty of time at that particular latitude.
"For a large object like this, dense pieces like parts of the rocket engines could survive re-entry and crash to Earth," Harvard-Smithsonian Center for Astrophysics astronomer Jonathan McDowell told CNN last year after April's crash.
"Once they reach the lower atmosphere they are travelling relatively slowly, so worst case is they could take out a house."
CZ-5B is 30m long and five metres wide, and observations from the ground suggest it is tumbling randomly, making any attempts to control it basically impossible.
Holger Krag, head of the Space Safety Programme Office for the European Space Agency, told Space News to expect between 20 and 40 percent of the 21-tonne rocket to make it through the atmosphere without burning up.
Last year's Long March rocket was the biggest uncontrolled reentry in 29 years. In 1991 Russia's 39-tonne retired Salyut-7 space station came down unexpectedly early, raining debris over an Argentinean town after overshooting its intended Pacific Ocean burial spot.
In 1979, parts of a US space station - Skylab - survived reentry and were scattered over parts of the Indian Ocean and Western Australia.
In 2018 the Chinese space programme lost control of a smaller space station, also called Tiangong, which crashed into the Pacific Ocean near Tahiti. Christchurch was in the nine-tonne spacecraft's path at one point.
Other regions CZ-5B will pass over in the next week include southern Europe, Australia, India, the US, southern Africa, Cuba, Brazil, the Philippines, Mexico, Thailand, Japan, Argentina, Madagascar, China, Papua New Guinea and Indonesia.
