Final module docks with China’s Tiangong space station

Huge Long March 5B rocket stage also in orbit with uncontrolled reentry expected in near future.

HELSINKI — A third module has arrived at China’s space station, completing construction of the country’s crewed orbital outpost.

A Long March 5B rocket lifted off from the Wenchang Satellite Launch Center at 3:37 a.m. Eastern Time on Oct. 31. Launch success was announced within 25 minutes of launch with the Mengtian module in low Earth orbit.

Mengtian used its own propulsion to match orbit and rendezvous with the Tiangong space station – currently in an orbit of around 380 by 387 kilometers – and connected to a forward port on the docking hub from Tiangong just under 13 hours after launch at 4:27 p.m. Eastern Time, China’s manned spaceflight agency, CMSA, confirmed.

The new experimentation module joins two previous modules: the Tianhe basic module and Wentian experiment module. Mengtian will soon be transposed to the port docking ring to complete the T-shaped arrangement of the space station. Wentian was transposed to the starboard mooring ring at the end of September.

Mengtian (“dreaming of the sky”) is a 17.9-meter-long, 4.2-meter-diameter, approximately 22-tonne module designed to accommodate a range of scientific experiments in research areas such as the physics of fluids, combustion and materials science and space. technologies.

It has a total volume of nearly 110 cubic meters, with about 32 cubic meters available for astronaut use, according to CMSA.

A view inside the Mengtian module before launch. Credit: CMSA

Mengtian also has a payload airlock that will allow the 5.2-meter-long small robotic arm launched with the Wentian module to grab science experiments and install them on payload adapters outside the module. The in-orbit release mechanism can deploy small spacecraft or CubeSats up to 100 kilograms into orbit.

The crew of three astronauts composing the Shenzhou-14 mission observed the events aboard Tiangong, awaiting the arrival of Mengtian.

Monday’s launch was the ninth of 11 missions scheduled for the construction and testing of Tiangong. The launch of a cargo spacecraft and the launch of a separate crew will complete this phase before the end of the year.

A Long March 7 rocket come in Wenchang on October 11 and will be assembled to launch the Tianzhou-5 cargo mission.

The launch of Tianzhou-5 could take place in the first half of November and will provide supplies for the next crewed mission Shenzhou-15. The Tianzhou-4 spacecraft will undock from Tiangong and de-orbit before these missions. Shenzhou-15 will be launched from the Jiuquan Satellite Launch Center in the Gobi Desert on a Long March 2F rocket as early as late November, after Tianzhou-5 arrives at Tiangong.

The arrival of Shenzhou-15 at Tiangong will see the first Chinese crew transfer and mark the start of the space station’s operational phase.

China plans to keep Tiangong occupied for at least 10 years, conducting scientific experiments, including international experiments under an initiative with UNOOSA. It could also accommodate foreign astronauts in the future.

China will add other capacities to the Tiangong in the future. The Xuntian Optical Module, a Hubble-class co-orbiting space telescope, is expected to launch in late 2023 or 2024.

Xuntian has a two-meter aperture and a 2.5 gigapixel camera. With its wide field of view, it aims to monitor around 40% of the sky in ten years. It will be able to moor at Tiangong for maintenance and repairs.

The space station itself could also be expanded from three to six modules, according to Chinese space officials. Such expansion may depend on other countries joining the project.

Arrival of stage 5B of the Long March

As with previous Long March 5B missions, the rocket’s large first stage has entered orbit and is expected to make an uncontrolled reentry sometime next week.

The US Space Force’s 18th Space Defense Squadron tracked Mengtian into a 179 x 323 kilometer orbit inclined at 41.46 degrees hours after launch, with the Long March 5B first stage in a 173 x 314 kilometer orbit.

The three previous launches of Long March 5B have notably seen the rocket’s large first stage enter orbit and make uncontrolled the returns. The previous launch sent the Wentian module into orbit and saw the first stage enter the atmosphere over Southeast Asia less than a week later.

It cannot be accurately estimated where and when the final empty stage of approximately 21 metric tons will fit. The stage will orbit Earth once every 90 minutes, with its orbit decay depending on atmospheric fluctuations.

Variables, including solar activity, which can inflate the atmosphere, causing greater drag at higher altitudes.

The China Academy of Launch Vehicle Technology (CALT), the maker of the Long March 5B, has not commented on the previous incidents. He has however declared passivation of depleted stages, including venting of remaining propellant depletion batteries, to prevent in-orbit debris-causing explosions in accordance with international practice.

The larger problem of uncontrolled rocket body re-entries is assessed in a journal Nature Astronomy paper published on July 11. He estimates that with current practices, there is a 10% chance that uncontrolled re-entries will cause one or more casualties over a decade.

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