The rocket successfully launched the Tianhe module last week, which will become the living quarters of the future Chinese Space Station (CSS). Unfortunately, the 30-metre long rocket also reached orbit, and is now one of the largest ever launches to make an uncontrolled re-entry.
It is uncommon for rockets to reach the velocity necessary to reach orbit, but it is currently travelling around the world once every 90 minutes, or seven kilometres every second. It passes by just north of New York, Madrid, and Beijing, and as far south as Chile and New Zealand.
There are fears that the rocket could land on an inhabited area; the last time a Long March rocket was launched in May 2020, debris was reported falling on villages in the Ivory Coast. The speed of the rocket means scientists still do not yet know when it will fall, but it is likely to do so before 10 May 2021.
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Will the debris hit anyone?
“Worst case [scenario] is one of the structural rods hits someone, potentially a fatality but unlikely to see multiple casualties”, Jonathan McDowell, Astrophysicist at the Astrophysics Center at Harvard University, told The Independent.
He added that the debris will be travelling at approximately 100 miles-per-hour, so there could be expensive property damage, but because it will be spread over 100 miles of along-track only one or two pieces are likely to hit a populated area.
Should we be afraid of falling debris?
As space agencies cannot predict where the rocket will fall, a detailed risk assessment for those concerned about falling debris is not available.
However, the ESA says that people should not be worried about being struck from falling debris.
“In general, most objects burn up entirely in the atmosphere during the re-entry. Parts of larger objects, or components that are made of material with a high melting point, may survive to reach the ground or ocean surface”, it says.
“As these are rare events, and as about 75 per cent of the Earth’s surface is covered by water while large portions of land area are uninhibited, the risk for any single individual is several orders of magnitude smaller than commonly accepted risks, such as those encountered when driving a car, taken in day-to-day life.”
Where will it avoid?
While we might not know where it’s going to land, but scientists know where Long March 5B is going to avoid.
Since CZ-5B’s orbit (the classification for the debris) is inclined at 41 degrees to the Earth’s axis, any debris will not fall further than that either north or south of the latitude.
“Therefore, the risk zone includes any portion of Earth’s surface between 41N and 41S latitude. This, briefly, and for what concerns ESA Member States, includes portions of Spain, Italy and Greece”, the ESA says.
What will happen when the rocket re-enters Earth
While it is likely that the rocket will fall into the ocean – simply due to the large percentage of the Earth being covered in water – astronomers believe that some pieces of the rocket will survive re-entry.
This would be the “equivalent of a small plane crash scattered over 100 miles”, according to Jonathan McDowell, Astrophysicist at the Astrophysics Center at Harvard University.
Right now, predicting the rocket’s fall is very difficult, but it is expected that it will return to Earth on 10 May. Once the specific day has been confirmed, experts can apparently narrow its landing time down to a six-hour window.
“The Long March 5B core stage is seven times more massive than the Falcon 9 second stage that caused a lot of press attention a few weeks ago when it re-entered above Seattle and dumped a couple of pressure tanks on Washington state,” McDowell also said. “I think by current standards it’s unacceptable to let it re-enter uncontrolled. Since 1990, nothing over 10 tons has been deliberately left in orbit to re-enter uncontrolled.”
Long March 5B: Tracking the rocket
Currently, the rocket is keeping within those parameters, but has dropped further today. At 10:00am GMT, when the rocket was over Africa, it dropped to nearer 160 kilometres.
Amateur observations from the ground show regular flashes from the rocket in the night sky, suggesting that it is not under any control.
It is likely much of the rocket will break down as it crashes, but some debris will remain.
“It is always difficult to assess the amount of surviving mass and number of fragments without knowing the design of the object, but a reasonable “rule-of-thumb” is about 20-40 per cent of the original dry mass,” Holger Krag, head of the Space Safety Programme Office for the European Space Agency said.