[As of early Friday, the U.S. Air Force’s Space Track Project estimated the debris will crash in a remote desert outside Mary, Turkmenistan, although researchers warned that with roughly a day left until reentry, the projected site could be wildly off-base.]
Chinese officials are “closely
observing” the reentry of the Long March 5B rocket and will “promptly report
news about the situation to the outside world,” Foreign Ministry spokesman Wang
Wenbin told reporters.
China has drawn criticism after its launch last month of the
rocket ferrying the core module of the Tianhe space station, with plans to let
the booster fall back through the atmosphere and land where it may.
Because the booster will be
reentering the Earth’s atmosphere at about 18,000 mph, it’s almost impossible
to predict where the trail of debris will hit until hours before reentry, which
is expected to occur late Saturday night Eastern time, within about an 11-hour
margin of error, according to the California-based Aerospace Corp.
Objects orbiting Earth stay in
space through a constant balance. While gravity tugs them toward Earth, their
forward momentum keeps them in space. Over time, minuscule amounts of air drag
slow an object, eventually knocking it out of orbit.
Most satellites and other
man-made objects are small enough that they burn up in the atmosphere. The
Chinese rocket, however, is bigger — so concern exists that pieces will survive
to hit the ground.
As of early Friday, the U.S. Air
Force’s Space Track Project estimated the debris will crash in a remote desert
outside Mary, Turkmenistan, although researchers warned that with roughly a day
left until reentry, the projected site could be wildly off-base.
Part of the uncertainty stems
from the rocket’s tumbling motion as it passes through the mesosphere, or an
outer layer of Earth’s atmosphere.
Changes in air density slow it
down at different rates that are tricky to predict. Modeling how the mesosphere
could affect the rocket’s speed is also complicated by constantly fluctuating
conditions on the sun.
The rocket’s gradual loss of
momentum means it’s approaching Earth’s surface at just 0.3 mph.
Wang said Friday that the rocket
is designed so that most of its components will burn up in the atmosphere
during reentry. “This is standard international practice,” he said. “The
probability of causing harm to aviation activities and the ground is extremely
low.”
When an object falls out of
orbit, how much debris makes it to the ground depends on the object’s size,
shape, mass and the melting temperatures of all materials used. Even the
biggest satellites produce a comparatively tiny amount of debris.
Although researchers say the
chances of the debris hitting populated areas are indeed minuscule, some have
called the Chinese mission irresponsible because the Long March husk, at 21
metric tons and almost 100 feet long, would be one of the largest objects to
ever reenter the Earth’s atmosphere on an uncontrolled trajectory.
A controlled reentry would entail
firing thrusters opposite to the direction of travel, slowing an object down
enough to enter Earth’s atmosphere over a predetermined remote area or ocean.
It’s not an exact science, but it reduces the chance of debris impacting
populated regions.
Chinese officials did not make
the necessary preparations for a controlled reentry.
As part of its design, the
Chinese sent the Long March into low orbit, where it has been drifting for days
at high speed, as opposed to other rocket launches that have let the booster
fall away more quickly and along a more predictable arc under the Earth’s
gravitational pull.
Astrophysicists have expressed
concern that episodes like this, featuring potentially hazardous
corner-cutting, could become more frequent in the absence of stricter
international law.
“There is at least a liability
convention that says if your country’s space object crashes in my country, I
can demand compensation, but I have to give the object back to you,” said
Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for
Astrophysics. “What there isn’t at the moment is what I call a ‘reckless
driving law.’ You only get to complain if it actually crashes. [China] should
not have left this big thing in orbit, but if they play the odds and get lucky
and it crashes in the ocean, we don’t really have any comeback.”
Although the chances of actual
human injury are astronomically small, close calls do happen: A farmer in
eastern Washington state found part of a pressurized helium container from a
SpaceX rocket launch in April. Last year, debris from another Chinese Long
March rocket landed in Africa and drew a rebuke from Jim Bridenstine, the NASA
administrator at the time.
Chinese state media this week
reacted angrily to the international scrutiny, saying its launch was being
unfairly maligned. State media reporters juxtaposed how U.S. media outlets
covered China’s “out-of-control space junk” in contrast to the SpaceX wreckage,
which was described as creating “a dazzling light show” over Pacific Northwest
skies.
The Tianhe space station, which
is expected to be the only operational space station after the retirement of
the International Space Station in the next four years, has been a point of
national pride for China, which has also completed a flurry of successful lunar
and Mars missions and has spoken of putting humans back on the moon.
“Hyping of the so-called China
space threat . . . it’s an old trick used by hostile powers every time they see
technological breakthroughs in China, as they are nervous,” the Global Times
quoted Song Zhongping, a former Chinese military officer and popular television
commentator, as saying.
U.S. defense officials said this
week that they were tracking the Long March debris and had no plans to shoot it
down.
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