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A
large Chinese rocket is set to make an uncontrolled reentry back into Earth's
atmosphere, but it is not yet clear exactly where or when the debris will hit
our planet.
China's Long March 5B rocket is
"unpredictably" falling back to Earth after launching a part of the
new T-shaped Chinese space station on Thursday local time in Wenchang, according to SpaceNews. The 22.5-metric-ton Tianhe space station module is in its correct
orbit after separating as planned from the core stage of the rocket, which is
now expected to re-enter in a few days or about a week.
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"It will be one of the largest instances of
uncontrolled reentry of a spacecraft and could potentially land on an inhabited
area," SpaceNews said. That said, the more likely possibility is the core
stage will fall in an uninhabited place like Earth's oceans, which cover 70% of
the planet. The odds of a particular individual being hit by space debris are
exceedingly low, once estimated at 1 in several trillion.
Plotting the trajectory of this falling rocket stage
is difficult, if not impossible because there are too many uncertainties
involved in calculating the effect of the atmospheric drag on the core module. Earth's atmosphere can expand or contract with solar activity, making it hard to
estimate exactly when and where the rocket will come down.
"The high speed of the rocket body means it
orbits the Earth roughly every 90 minutes and so a change of just a few minutes
in reentry time results in reentry point thousands of kilometers away," SpaceNews said, adding that the object's orbital inclination of 41.5 degrees
means it "passes a little farther north than New York, Madrid and Beijing
and as far south as southern Chile and Wellington, New Zealand, and could make
its reentry at any point within this area."
The rocket's anticipated return numbers among several large debris events of the last few decades, including the Chinese Tiangong space
station and Europe's Gravity field and steady-state Ocean Circulation Explorer
(GOCE). That said, most of the debris tends to burn up in the atmosphere and
only the very largest pieces would come down to the ground. Launching states
also generally try their best to point a returning piece of debris back to
Earth and to give estimates for where it may fall.
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On Twitter, spaceflight observer and Harvard
University astrophysicist Jonathan McDowell plotted the return of the Long March 5B against other large debris events, not least
of which was the uncontrolled return of NASA's 76-ton Skylab space station
nearly 42 years ago. Ground controllers were able to steer the space station somewhat over its planned reentry point over the Indian Ocean, but
the debris track stretched much further than expected.
"To summarize: this one is bigger than anything
recent, but not as big as Skylab and its ilk back in the day," McDowell said on Twitter of the Long March 5B's return.
China plans a busy
construction schedule on the space station, with state media reporting the
construction should be finished by the end of 2022. Much like the International Space Station, the
Chinese complex will include several modules, requiring 10 additional launches:
two more module launches, four crewed missions and four cargo vessel flights,
as reported by China Global Television Network (CGTN).
It's impossible to predict when and where China's Long March 5 rocket, a
CZ-5B, will crash down to Earth. But
it will. The question is: What's the risk?
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