A 30 m long, 17-8 tonne Chinese rocket-stage fell into the Atlantic Ocean off the coast of Mauritania, slightly after 3.30 pm GMT on Monday 11 May 2020, from the Wenchang launch centre on Hainan Island in southern China. The piece of space junk was the main rocket stage of a Long March 5B heavy launcher which took off on Tuesday 5 May. The rocket was initially lifted from the ground by three smaller kerosene fuelled rocket boosters, then powered the main lift of the spacecraft by using a cryogenic hydrogen system. The rocket delivered a prototype manned crew capsule (without any crew) into orbit, and was expected to burn up high in the atmosphere as it fell back. However, the much of the body appears to have survived, and was tracked by the US Air Force, passing over New York about 15 minutes before eventually vanishing off the coast of Mauritania.
The trajectory of the Long March 5 rocket-booster (orange line), and it's last known location. Jonathan McDowell/Twitter.
Pieces of space junk re-entering the atmosphere, and even reaching the ground (or sea) are not that unusual, but objects of this size are somewhat rare, with the last object of this size having been the 39 tonne Soviet Salyut 7 Space Station in February 1991, which crashed into the Pacific Ocean southern Pacific Ocean. The Colombia Space Shuttle, which was disintegrated during re-entry in February 2003 is not usually counted as 'space junk' as it was manned, but weighed 2000 tonnes, so this could be considered the largest such object.The Russian Fobos-Grunt Probe, which fell into the Pacific Ocean in January 2012, after an unsuccessful launch in November 2011, weighed about 13 tonnes.
The re-entry orf the Long March stage was planned, but it's survival into the lower atmosphere was unexpected, as it was essentially a hollow tube. It is possible that only the rocket engines survived re-entry, reducing the size of the object at impact. In either event, a returning rocket launcher presents a far lower risk to anyone on the ground than an asteroid of similar mass, as its velocity is much lower, with asteroids travelling far faster due to their orbital velocity, as their trajectory seldom matches that of the Earth.
The launch of the Long March 5B heavy launcher from Hainan Island on 5 May 2020. CNN.
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