China is gearing up to send a second module to its under-construction space
station with a launch from the coastal Wenchang spaceport later this month.
A Long March 5B heavy-lift rocket will launch the roughly 22-ton Wentian
experiment module around 02:20 a.m. ET (0620 UTC) July 24, according to
recently announced area clearance notices consistent with such a launch.
The 53.7-meter-long, 837.5 metric ton rocket will be rolled out to the pad
at Wenchang in the coming days.
Wentian is expected to rendezvous and join Tianhe, the similarly-sized core
module for the Tiangong space station which launched in April 2021. Tianhe
made orbital adjustments earlier this month to prepare for the arrival of
Wentian.
The new module has a length of 17.9 meters and a maximum diameter of 4.2
meters. It features crew quarters and an airlock cabin which will become the
main exit-entry point for extravehicular activities (EVAs) once active,
replacing the role now played by the Tianhe docking hub.
The new crew facilities will allow China to perform a first crew handover.
This will take place when the current Shenzhou-14 crew greet three new
astronauts due to fly aboard Shenzhou-15 in December. Tiangong will then
host six astronauts for a period of days.
Its main role is hosting experiment racks for science experiments, while
also providing backups to the life support and control functions of Tianhe.
Wentian carries a five-meter-long robotic arm, supplemental to the
10-meter-long Tianhe arm. The two arms can also join together.
Wentian will also come with 30-meter-long solar arrays, boosting the power
available to Tiangong. Wentian will host a new round of live science
lectures, following on from those presented by the Shenzhou-13 crew aboard
Tianhe.
“Wentian is a critical stage in the building of China’s space station,” says
Brian Harvey, author of China in Space: The Great Leap Forward. “The Tianhe
crew has overseen numerous undockings and redockings, so such maneuvers are
well practiced, but nothing can be taken for granted, especially for the
first time.”
The Shenzhou-14 astronauts aboard Tianhe have been undergoing a training
program including rendezvous and docking operations and using Tianhe’s
mechanical arm in preparation for the arrival of Wentian.
Tianzhou-2, a cargo craft initially charged to deliver supplies to Tianhe
for the first crew, Shenzhou-12, was used early this year for a
transposition test to verify procedures for moving a module from the forward
docking port and towards a lateral port.
Tianhe has so far been visited by three separate three-person crews. The
most recent, Shenzhou-14, arrived on June 5 and will oversee the arrival of
Wentian and Mengtian, another 22-ton experiment module scheduled for launch
in October.
The arrival of the latter will complete the planned T-shaped Tiangong space
station, though China has suggested it could later expand the complex to six
modules.
“The real work of the station, which we can expect to fly into the 2040s,
will begin,” Harvey says, once Mengtian is docked in position.
The Chinese space station was first envisioned in 1992 with the approval of
Project 921 which called for the development of human spaceflight
capabilities. The project suffered delays due to issues with development and
performance of the Long March 5B, but could also be expanded to six modules
and most commercial and tourist missions.
The country also plans to launch a co-orbiting optical telescope module,
named Xuntian, in late 2023. It will be capable of docking with Tianhe for
repairs, maintenance, refueling and upgrades, and aims to survey 40 percent
of the sky across a decade.
Xuntian features a two-meter-diameter aperture and a field of view more than
300 times greater than the 32-year-old Hubble Space Telescope. NASA plans a
new survey mission, the Nancy Grace Roman Space Telescope, around 2027.
Wentian fallout?
The two previous Long March 5B launches, which carried a test new generation
crew spacecraft prototype and the Tianhe module respectively, notably saw
the large first stage of the rocket enter orbit and make uncontrolled
reentries.
Attention will be on whether or not the launch profile has been altered or
deorbiting capabilities, such as restarting engines, have been added. If
not, the mission could see another uncontrolled reentry occur.
Exceptionally, the Long March 5B includes a core stage and boosters.
Usually smaller second or further stages do the final work to carry a
spacecraft into orbit, with the larger first stage cutting off before
reaching orbital velocity and falling within a calculated, safe area.
Chinese foreign ministry spokesperson Wang Wenbin stated last year that it
was “common practice across the world for upper stages of rockets to burn up
while reentering the atmosphere.” In this case, the large first stage is
also the upper stage.
While such an event would involve particularly large and massive spacecraft,
the standalone threat of the spent rocket stage causing damage or harm will
be very low. Most of the stage will burn up in the atmosphere and is likely
to land in the oceans or uninhabited areas.
There is however a larger cumulative risk, according to academics, from
uncontrolled reentries stemming from space launch activities.
Area clearance notices provide drop zones for the boosters and payload
fairings for the upcoming Wentian launch, but no indication of a zone for
the first stage.
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Space & Astrophysics